Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
rsta.royalsocietypublishing.org
CO2 utilization: an enabling
element to move to a resourceand energy-efficient chemical
and fuel production
Review
Claudio Ampelli, Siglinda Perathoner
Cite this article: Ampelli C, Perathoner S,
Centi G. 2015 CO2 utilization: an enabling
element to move to a resource- and
energy-efficient chemical and fuel production.
Phil. Trans. R. Soc. A 373: 20140177.
http://dx.doi.org/10.1098/rsta.2014.0177
and Gabriele Centi
One contribution of 18 to a discussion meeting
issue ‘The new chemistry of the elements’.
Subject Areas:
green chemistry, chemical engineering,
environmental engineering, environmental
chemistry
Keywords:
CO2 utilization, sustainable chemical
production, resource and energy efficiency,
chemical industry future
Author for correspondence:
Gabriele Centi
e-mail: [email protected]
Department of Electronic Engineering, Industrial Chemistry and
Engineering, Section Industrial Chemistry, University of Messina,
INSTM/CASPE (Laboratory of Catalysis for Sustainable Production
and Energy) and ERIC (European Research Institute of Catalysis),
V.le F. Stagno D’Alcontres 31, Messina 98166, Italy
CO2 conversion will be at the core of the future of
low-carbon chemical and energy industry. This review
gives a glimpse into the possibilities in this field by
discussing (i) CO2 circular economy and its impact
on the chemical and energy value chain, (ii) the role
of CO2 in a future scenario of chemical industry, (iii)
new routes for CO2 utilization, including emerging
biotechnology routes, (iv) the technology roadmap
for CO2 chemical utilization, (v) the introduction
of renewable energy in the chemical production
chain through CO2 utilization, and (vi) CO2 as a
suitable C-source to move to a low-carbon chemical
industry, discussing in particular syngas and light
olefin production from CO2 . There are thus many
stimulating possibilities offered by using CO2 and this
review shows this new perspective on CO2 at the
industrial, societal and scientific levels.
1. Introduction
CO2 has long been considered a waste and a cost (in
countries applying carbon taxes), but interest is rising
in the possibility of chemical utilization as well as in
producing solar fuels. Many reviews and books have
discussed the different options for converting CO2 . A
selection covering the different aspects of the broad
2015 The Author(s) Published by the Royal Society. All rights reserved.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Notwithstanding these positive indications, the general opinion about the chemical use of
CO2 is of an area with (and that will still have in the future) a very minor impact in terms
of its contribution to the reduction of greenhouse gas (GHG) emissions. For example, the
Intergovernmental Panel on Climate Change (IPCC) reported that: ‘the use of captured CO2 in
industrial processes could have only a minute (if any) effect on reduction of net CO2 emissions’
[26]. Also, in terms of the specific impact on the chemical and energy industry, it is often argued
that the utilization of CO2 will be limited to small, niche applications and in general will not
have a major impact on chemical production. A general remark is that CO2 is the end product of
chemical or energy production and has a low thermodynamic energy value. Thus, a lot of energy
is required to transform CO2 into useful chemical or energy products (energy may be transferred
directly or through a reaction with high-energy molecules). This is supposed to determine the
high costs of production. It is possible to turn this limitation into an opportunity, by using the
process of converting CO2 to higher energy density compounds as an effective way to insert RE
into the chemical production chain, as discussed later. The supposed low potential impact of CO2
chemical utilization is derived from the wrong vision of its potential uses, as also discussed later.
The field of CO2 chemical utilization is thus still largely influenced by misconceptions about the
real potential and impact.
The objective of this review is thus quite different from the many reviews and books on CO2
utilization mentioned before. The aim is not to provide a systematic overview of the different
possibilities and reactions of CO2 and/or of related aspects such as the characteristics of the
catalysts necessary to efficiently perform these reactions. However, novel opportunities will be
highlighted to evidence how the use of CO2 will be a critical enabling element for the sustainable
future of chemical production and to move to a resource- and energy-efficient production. We will
discuss how large the impact on GHG emissions will be—potentially no less than that expected
.........................................................
— Advanced materials: a pilot plant opened at Bayers Chempark in Leverkusen, Germany, in
February 2011 [21] to produce high-quality plastics (polyurethanes) based on CO2 ; other
industrial initiatives are in the area of the production of polycarbonates from monomers
derived from the reaction of epoxides (propylene oxide, for example) and CO2 .
— Fine chemicals: DNV (now DNV GL) has developed a pilot unit for the electrochemical
reduction of CO2 to formate salts and formic acid [22]; various fine chemicals of industrial
interest (carbamates, urethanes, isocyanates, etc.) may also be produced using CO2 as a
co-reactant.
— Intermediate chemicals: BASF is actively working to develop catalysts to produce acrylic
acid from ethylene and CO2 [23,24], as an alternative to the bio-based route developed
by Arkema and BASF—acrylic acid from glycerol; both these routes are proposed to
overcome high propylene prices in the current oxidation route. Other intermediates
produced using CO2 involve biotechnology routes; for example, acetone synthesis
(Evonik) or succinic acid production (Bioamber, Roquette, BASF, Mitsubishi Chemicals,
etc.).
— Base chemicals/fuels: in September 2011 CRI opened a plant in Svartsengi (Iceland) for
synthesizing 5 Mton yr−1 of methanol from CO2 using H2 produced electrolytically from
renewable energy (RE) sources—mainly geothermal [25]; other companies, such as Mitsui
Chemical, are exploring the production of base chemicals from CO2 .
2
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
range of CO2 chemical use is presented in [1–20]. The rising academic and industrial interest
is shown, for example, by the number of results in a SciFinder search with the keywords ‘CO2
conversion’. In 2003, the number of entries were about 180 for books, journals and reviews
and about 15 for patents; these entries rose to approximately 650 and 100, respectively, in
2013. Scientific and industrial initiatives towards the chemical utilization of CO2 have increased
substantially over the last few years [8] and there is increasing industrial attention to produce
different types of chemicals and fuels from CO2 :
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
3
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
from carbon capture and storage (CCS) technologies or the use of biofuels, but with significantly
lower costs [27].
A further objective is to show how some of the grand challenges faced by our society (mitigate
climate change, preserve the environment, use of RE and replace fossil fuels) share a common
aspect [28]: the (re)use of CO2 to produce fuels and chemicals is an enabling factor to overcome
these challenges. Reusing CO2 not only addresses the carbon balance in the Earth’s atmosphere
with the related negative aspects on the quality of life and the environment, but also represents a
valuable C-source to substitute fossil fuels [18,19]. By using RE sources for the conversion of CO2 ,
it is possible to introduce RE into the production chain, in a more efficient way than alternative
possibilities [7,29]. The products derived from the conversion of CO2 (such as methanol, light
olefins, etc.) effectively integrate in the current energy and material infrastructure, thus allowing a
smooth and sustainable transition to a new economy without the very large investments required
to change this infrastructure [29,30]. In close collaboration with the use of biomass, the use of CO2
provides a new sustainable scenario for chemical production [31–33] and to move biorefineries to
biofactories [34,35].
Often in discussions on the possible ways to use CO2 , the need to employ long-term
sequestration of CO2 to reduce GHG emissions has been considered necessary, because having
a short cycle time means that carbon is returned to the atmosphere quickly. This is not a correct
analysis, when RE is incorporated in the final molecule of CO2 transformation. A short cycle
time, for example when CO2 is converted to methanol using the H2 produced by RE sources
and then methanol is used as a fuel, means that in every cycle there is a minus delta in
carbon emissions that is derived from the substitution of fossil fuels with less-carbon-intensive
sources. On a certain time scale (20 years, for example), the long-term sequestration of CO2
has a single impact, while for short-time cycles there is a cumulative effect. The exact value
derives from a life cycle analysis (LCA), but, on average, the effect is at least one order of
magnitude higher in short-time cycles than in long-term sequestration. As discussed below,
the reason to incorporate RE in CO2 transformation molecules (fuels) derives from the need
to store/transport energy and to extend its range of utilization. Thus, recycling of CO2 with
incorporation of RE in the transformation process enables new routes for using low-carbon
energy sources.
In a longer term visionary idea, it is possible to create a CO2 economy, where it will be possible
to achieve full circle recycling of CO2 using RE sources, in analogy with how plants convert CO2 to
carbohydrates and O2 through photosynthesis but intensifying the process and especially being
able to control the type of final products [36–39]. Capture and conversion of CO2 to chemical
feedstock could provide new routes to a circular economy and move to Economy 3.0. One of
the pillars of the latter is the realization of a distributed and personalized energy (and perhaps
chemical) production.
This review aims not only to show and discuss this new vision on CO2 at the industrial, societal
and scientific levels but also to provide evidence on how CO2 conversion will be at the core of the
future of chemical industry. It will start by briefly introducing the future of the chemical industry
and the role of CO2 in enabling a sustainable scenario, moving then to an analysis of some of the
recent developments in the industrial chemical use of CO2 . Emphasis is placed especially on CO2
hydrogenation with H2 produced from RE sources. Some limited indication is given on the use of
CO2 to produce advanced materials. This topic is discussed in various other reviews and books
[8,13,17–19]. Some new possible routes of CO2 utilization, although still at the laboratory scale,
are also discussed in §3.4, together with new possibilities offered by revising well-established
routes such as urea synthesis (§3.5). Emphasis is placed on the emerging opportunities for CO2
utilization by biotechnological routes (§3.6), because this is an aspect that is still not adequately
covered, despite having a large potential for innovation.
A technological roadmap for CO2 chemical utilization based on this survey of emerging
possibilities as well other state-of-the-art analyses is discussed. Aspects discussed in this section
include assessing the different routes, the social perception of CO2 utilization paths and an
analysis of the emerging patent literature. The next section deals with the key question of the use
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
biofuels
4
fossil fuels
45
47 3.5
49.5
residential
energy
products
chemical raw materials
industry
CO2
intermediates
monomers
renewable
energies
(H2O
polymers
fine chemicals
consumer products
H2)
consumers and industry
disposal
Figure 1. A model of CO2 circular economy and its impact on the chemical and energy value chain. (Online version in colour.)
of CO2 utilization to introduce RE into the chemical production chain, which is a crucial element
in the move to a resource- and energy-efficient process industry and thus for the sustainability
of this important manufacturing sector. Emphasis is especially placed on producing ‘renewable’
methanol because we believe that this is one of the preferable routes. A discussion on the possible
impact on the ecosystem of this path is also given, together with some elements of methanol use
and market perspectives.
The final section gives a brief overview of the use of CO2 as a valuable carbon source,
with emphasis in particular on the production of basic raw materials, because this is a key
issue in moving to low-carbon chemical production. Aspects discussed regard, in particular,
the production of syngas and light olefins from CO2 . Although it was not possible to
systematically cover all aspects in this scientific area of rapidly rising relevance and the number
of papers and ideas because of space restrictions, we hope that this overview will give a good
glimpse of how CO2 utilization will play a major role in shaping the future of chemical and
energy production.
(a) CO2 circular economy and its impact on the chemical and energy value chain
Figure 1 shows in a concise way the concept of CO2 circular economy. Current economy is largely
based on the use of fossil fuels, but already at the stage of transformation of fossil fuels to the
energy products or the raw materials used for chemical production, nearly half of the original
energy content is lost in the form of CO2 , as shown in figure 1.
Various other losses are present in downstream processes, before utilization of the energy
or chemical products. Even in the process of production of biofuels, large amounts of CO2 are
formed (approx. 1 ton CO2 per ton of ethanol, for example). We could thus say that our current
society is not fossil fuel centred, but CO2 centred. Through the (re)use of CO2 , it is possible to
re-balance this economy, allowing a more effective use of RE (as discussed below), providing
new raw materials for chemical production and especially preserving the actual value chain. The
latter is a very important element because it allows the costs of transformation to new sustainable
production systems to be minimized.
.........................................................
100
55
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
transport
electrical
energy
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
— Pushing forces: related to raw materials, technology developments, etc.
— Pulling forces: related to social demand (market demand, security, environment and
quality of life).
The consequence is a nonlinear evolution due to the different dynamics of these forces [43] and
the synchronisms with developments in other industrial areas. There is a cyclic evolution with
periods of renewal, prosperity, recession and depression, which are known as macro-economic
cycles of Kondratieff [44,45]. We are at the end of one of these cycles [45]. The new one will
be dominated by a change in raw materials (with respect to the dominant use of oil; this has
happened in all the preceding cycles), reorganization of the energy and resource infrastructure,
switch to renewable energies and drivers for sustainability, largely influencing the market and
industrial objectives [45]. The consequence is that the chemical industry is at a turning point
with a major change expected in its structure within a relatively short time (one to two decades
maximum). Science and technology should provide the basis to enable this transition, and there
is thus an increasing need to find new raw materials to substitute for fossil fuels in the production
of chemicals and polymers (and energy), and new production methodologies which decouple
production from the scale-economy. The latter was the characterizing element of the last economic
cycle of chemical production, and also one of the limiting factors in the move to sustainable
production [44].
There are many major changes in chemical production that are necessary for the industry
to respond to the need for a resource- and energy-efficient sustainable future and to move to
a low-carbon economy. The use of alternative raw materials is among these driving forces, as
are biomass as chemical feedstock, (re)use of CO2 , waste valorization, use of RE, use of fossil
fuel alternatives to oil (actually accounting for the majority of petrochemistry production), and
use of shale gas instead of coal [31–34]. Figure 2 schematically represents the change from the
current (oil-centred) petrochemistry to the future of chemical production based on a larger use of
.........................................................
Discussing the role of CO2 utilization, as an enabling factor to move to a resource- and energyefficient chemical production, requires analysing briefly what the future may hold for the
chemical industry, that is, a short discussion on the new scenario [31–33] and the driving elements
determining the evolution. We limit the discussion here to some aspects that put the discussion
about the technology roadmap for CO2 utilization in the right perspective and that help to
understand the effective impact. Some further aspects can be found in [31–33].
It must be remarked that scientists commonly do not use scenario analysis, even though it is a
typical economic tool. However, it is an important tool to anticipate priorities. In general, it allows
(i) early identification of key technology bottlenecks, (ii) recognition of opportunities, R&D paths
and barriers, and (iii) anticipation of research macro-trends. It is thus clear that a discussion on
the impact of CO2 utilization paths on the future of the chemical industry should be linked to an
analysis of our future scenario, the correct assessment of which could allow us to identify early
the possible routes that have a higher probability of becoming effective industrial routes (out of
minor uses). On the other hand, scenario analyses are often based on a nearly linear extrapolation
of future directions as well as a limited understanding of the possible impact of new technologies
and how they can open new paths or what are the bottlenecks limiting these paths. It is thus not
possible to use only the developed scenarios, but it is necessary to analyse them in more detail.
Various studies have been carried out recently on the future of the chemical industry [40–42],
mainly from an economic perspective, although it should be made clear that they also suffer from
some of the remarks made earlier. A main observation is that the evolution trends in the chemical
industry are not linear, being the result of
5
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
2. What is the future for the chemical industry and the role of CO2 in this
industry?
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
biomass
6
aromatics
today
new low-carbon
raw materials
market products
energy
coal
raw materials
CO2
biomass
aromatics
oil
alternative
fossil fuels
NG
olefins
1
intermediates
syngas/H2
energy
market products
coal
1 light alkanes
clean renewable
energy
H2O
Figure 2. Change from the current (oil-centred) petrochemistry to the future of chemical production based on a larger use of
alternative raw materials and of renewable energy sources. NG, natural gas. (Online version in colour.)
alternative raw materials and of RE sources. We will discuss in the following sections the role of
CO2 utilization in this general panorama.
Globalization of chemical production is a major element characterizing the current landscape,
but there are several indications of how moving to a de-globalization will characterize the
future of chemical production. In fact, widening the type of raw materials, with emphasis on
local resources (due to various economic and social pushes), will determine a move towards
de-globalization and tighter integration with other industrial sectors (symbiosis, synergy, etc.),
as already observed in some cases. This will determine different regional ‘pressures’ to use
alternative raw materials. In regions such as Europe that lack other resources, CO2 (re)use will
play a major role in maintaining competiveness and in moving to a low-carbon economy [31–34].
It is important to take account of all these aspects when considering the role of CO2 in a future
scenario for chemical production, which may be different in Asia with respect to Europe or the
USA. The following considerations will apply especially to Europe, due to the higher social
and political pressure (translating into targets for substituting fossil fuels, use of RE, etc.) on
addressing the GHG issue, use of renewable energies and the move to a low-carbon economy.
Furthermore, there is a lack of other raw materials; therefore, waste biomass and CO2 can be
considered as Europe’s own resources. However, it is likely that Europe will be the driving force
behind spreading the chemical utilization of CO2 worldwide.
3. Recent advances in the industrial chemical use of CO2
CO2 as a feedstock for producing chemicals represents an interesting challenge both commercially
(as low-cost alternative raw materials, to produce novel valuable materials and to lower the
impact of production) and for innovation (to explore new concepts and new opportunities for
catalysis and industrial chemistry). The utilization of CO2 is an excellent opportunity to inject RE
in the energy or chemical production chains, as discussed below. This is a major problem faced
by the chemical industry, which is looking at new possibilities to increase its efficiency in the use
of resources and energy.
.........................................................
NG
future
intermediates
syngas/H2
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
olefins
oil
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
SNG
FT*
+ H2 – H2O
CO + H2
CO2
+ H2O
FT
+ CH4 – H2O
DR
bioroutes
+ H2
>C1 alchols
–[CH2]n–
diesel
>C1 hydrocarbons
+
HCOOH
H2
hydrogen storage/transport
fuel cells
electrochemical routes
solar thermal routes
chemical routes: FT: Fischer Tropsch (FT* modified FT)
DR: dry reforming
RWGS: reverse water gas shift
(catalytic)
SR: Sabatier reaction
Figure 3. Possible routes for CO2 hydrogenation with incorporation of RE in the process. SNG, substituted natural gas. (Adapted
from [7].) (Online version in colour.)
The chemical transformation of CO2 is a dynamic field of research, in which many industrial
initiatives also thrive, even if it is not always easy to understand the real opportunities and
limitations of each option [8]. The next section on the technology roadmap will attempt to define
the panorama for the industrial utilization of CO2 based on the analysis of the state of the art,
including recent trends in patents.
In a short-to-medium-term perspective, CO2 utilization will continue its progression
especially in areas that are technologically more advanced (e.g. CO2 -containing polymers, CO2
hydrogenation). The use of CO2 conversion to exploit unused RE resources or to mitigate
instabilities on the grid (related to the discontinuous production of energy by renewable sources;
thus, chemical conversion is a way to store and distribute energy) will play a future relevant role,
as discussed below. These driving elements will lead the way to increased use of CO2 .
In the long term, CO2 utilization will become a key element in sustainable low-carbon
economy in chemical and energy companies, combined with curbing consumption [27]. CO2
will become especially a strategic molecule for the progressive introduction of RE resources
into the chemical and energy chain [7,31], thus helping to lessen fossil fuel consumption. CO2
utilization will become an important component of the strategy portfolio necessary for curbing
CO2 emissions (with an estimated potential impact of gigatons equivalent CO2 emissions, similar
or even superior to the impact of CCS and biofuels, but with a lower cost for society [27]). CO2
utilization will thus be at the heart of strategies for sustainable chemical, energy and process
industries, for resource- and energy-efficient development.
In terms of potential application, the time to market (in relation also to the degree of
technological maturity), bottlenecks and limiting factors, market incentives and potential impact
on chemical production are among the main factors to be considered. The discussion in the
next section on the technology roadmap for CO2 chemical utilization will address some of
these aspects.
(a) CO2 hydrogenation
CO2 catalytic hydrogenation is the technology with the greatest possibility of shortly being
commercialized on a large scale. There are many possible routes, to methanol or DME, methane,
light olefins, above C2 hydrocarbons or alcohols, etc. An overview of the different CO2
.........................................................
gasoline
C2, C3 olefins
–[CH2]nOm–
+ e –, H +
RWGS
–
+e ,H
CO2
7
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
CH4
– H2O
+ H2 R
S
fuel cells
– H2O
CH3OCH3
CH3OH+ CH
3OH
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
8
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
conversion routes by hydrogenation is shown in figure 3. The routes are multi-step (e.g. H2 is
produced, for example, by water electrolysis using electrical energy from renewable sources and
then it is used in a catalytic process) or integrated (with formation of H2 equivalents, e.g. protons
and electrons are produced in the electro- and photocatalytic processes as well as in bio-catalytic
processes). In all these processes, RE is incorporated in the final product of CO2 hydrogenation.
Production of renewable H2 (by electrolysis using RE) and then its use in catalytic processes is
the current state of the art, with various processes (methanol, DME, methane, syngas and FT
processes) at a semi-commercial stage of development. In the future, integrated processes will
grow in relevance, because they allow a potential better efficiency, but productivities are still
too low.
Between the various routes outlined in figure 3, we believe that methanol formation is the
preferable one. There are various reasons related to the degree of maturity of the technology such
as the formation of a liquid product that is easy to store and distribute as well as very versatile
use in applications going from fuels to chemicals and not least because it uses relatively easy
technology (reduced steps, high selectivity and simpler separation). A semi-commercial unit in
Iceland run by CRI is in operation and pre-commercial industrial plants are under evaluation (for
example, by Mitsui Chemicals in Singapore).
Methane from CO2 (P2G) is another area in which there is strong R&D effort, particularly
in Germany, in relation to the local storage of excess electrical energy (from wind) and the
production of methane for automotive use (Audi e-gas process). A 6-MW P2G, located in the
Lower Saxony city of Werlte, started operations in 2013. As methane is a gas, storage and
distribution is more difficult than for methanol (even considering the large pipeline net; there are
also issues of purity for introduction in the pipeline system) and chemical use is quite difficult, if
not passing through syngas (but then direct production of syngas from CO2 would be preferable).
While various stakeholders, in particular in Germany, consider that this option will play a
major role in future energy systems as the infrastructure already exists and the storage capacity
(mainly underground in salt caverns, but present only in some areas) is very large, we do not
feel that this indication is fully correct. First, P2G is limited to using excess RE production, for
example from wind during the night. Therefore, the impact itself is limited. Second, from the
energy efficiency perspective, the synthesis of methanol, working at milder conditions and using
less H2 , is more efficient. Third, a gas in comparison with a liquid fuel has many constraints in
terms of storage, distribution and uses, including for chemical purposes.
The challenge for a future energy sustainability system is to enable an oil-equivalent energy
system, where RE can be traded on a world scale [27]. It is thus necessary to produce a liquid fuel,
rather than a gas, as demonstrated by the comparison between oil and natural gas (NG). There are
many countries worldwide where RE sources can be traded by converting them into a liquid fuel
that is easy to transport and store. The need for a pipeline infrastructure, as for methane, greatly
limits the type of exploitable RE sources. Thus, we believe that P2G will have a minor impact on
the chemical production value chain, although it will play a role in a future energy system.
Formic acid has minor uses for chemical production, if it is not being used as a carrier for
transporting H2 . The synthesis of higher alcohols and hydrocarbons through Fischer–Tropschtype reactions leads to a broad range of products, with resulting high costs of separation.
However, the production of light olefins (C2–C4) through a Fischer–Tropsch-to-olefin is an
industrially interesting process [46,47], for the higher added value of olefins with respect to
methanol. It is estimated that methanol synthesis from CO2 will become commercial within a
few years (see later section, in relation to the use of this reaction to import remote RE sources),
while light olefins from CO2 will require more time, because of other competitive possibilities
including from biomass [32].
The main issue is the cost (and carbon footprint) of H2 necessary for the reaction.
Actual electrolysers allow an efficiency of approximately 70–85% with energy consumption
of 4–6 kWh Nm−3 of H2 produced. Using RE, the efficiency decreases to about 60%, but the
hydrogenation of CO2 decreases the intrinsic energy by only a minimal amount, and thus
the main parameter influencing the carbon footprint is the production of H2 . Improvement
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
in the production of renewable H2 , however, is a necessary key element to establish
the commercialization of the CO2 hydrogenation processes.
(c) Sources of CO2 and costs
Often there is a problem regarding the recovery of CO2 and its purity. This is an important
aspect, but we do not feel that it is a critical one, at least in the initial stage of commercialization
of CO2 utilization technologies. In fact, there are many large-volume sources of rather pure
CO2 in refinery and chemical processes (ammonia production, ethylene oxide production, gas
processing, H2 production, liquefied natural gas, Fischer–Tropsch synthesis coal) as well as from
biorefineries (fermentation processes [35]). In the initial phase of introduction of technologies for
CO2 chemical utilization, the recovery of CO2 from the flue gases of combustion processes, with
the related problems of purification from contaminants, is thus not necessary.
It is estimated that globally approximately 500 million tons of low-cost (less than US$20 per
ton) high-concentration CO2 is available annually as a by-product from natural gas processing,
fertilizer plants and some other industrial sources. This amount does not include the CO2
emissions from biorefineries, which can double this figure. CO2 emissions from fermentation
processes are characterized by a high-purity level. At a higher cost, over 18 000 million tons could
also be captured annually from the dilute CO2 streams currently emitted by power, steel and
cement plants.
As commented at the end of the Introduction, the incorrect belief that the value of the
contribution of CO2 to climate change goals is limited to its sequestration effect must be overcome.
Instead, the key is its value to enable new low-carbon routes of RE use, with the related decrease
in GHG emissions. Account should be taken not only of the ‘sequestration’ of CO2 , but also of
how its reuse enables the reduction of GHG emissions on an LCA basis. By accounting in this
way, the misconception that the use of CO2 to make fuels (by using RE) does not contribute to
climate change goals when CO2 derives from fossil fuels is overcome.
The cost of CO2 capture is decreasing rapidly and market prices for CO2 will decrease when
restrictions on CO2 emissions are introduced worldwide. The revenue generated from reuse
will be inadequate to drive the development of CCS for power, steel and cement plants, but is
a current incentive for developing chemical reuse of CO2 as a C-source, to prepare advanced
materials (polymers), to develop new synthetic routes and in storage/transport of RE. Therefore,
the perspectives on CO2 utilization are quite positive.
(d) New routes for CO2 utilization
The last 2–3 years have seen a rapid increase in the number of publications, with many proposed
new routes for activating CO2 using homogeneous catalysts [49], for example
— hydrosilanes used to convert CO2 into methane or methanol using zirconium phenoxide
borane complexes or N-heterocyclic carbenes as catalysts [50,51];
— borane reduction of CO2 to form boryl formats using nickel diphosphine complexes as
catalysts [52];
.........................................................
For the use of CO2 in producing advanced materials, particularly polymers, and also fine
chemicals, the driving factor is the possibility to develop alternative synthesis routes, rather than
to reduce GHG emissions. There are various industrial initiatives in this sector, among which are
the above-mentioned Bayer initiative (focused especially at producing polyoils for polyurethane),
BASF initiative (for polypropylene carbonate) and Novomer Inc. initiative (for a polypropylene
carbonate) [8]. Although it is already commercial, the Asahi Kasei’s process for phosgene-free
production of aromatic polycarbonate starts from ethylene epoxide, bisphenol-A and CO2 [48].
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
(b) CO2 use to produce monomers for advanced materials
9
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
(e) Revising old routes: urea synthesis
There are also interesting new industrial possibilities in revising old routes, particularly urea
production, which is well established on a large scale (over 120 Mton yearly production).
However, opportunities to improve it are emerging. Urea boosting indicates the capture of an
external current of fossil CO2 for urea production in an integrated ammonia–urea manufacturing
plant, and that uses natural gas as a feedstock in the reforming process to produce CO2 and NH3 .
When natural gas is used as a feedstock, an excess of NH3 is produced. An external source of
CO2 can be delivered via a pipeline to the urea plant and reacted with surplus ammonia to form
urea. This solution mitigates GHG emissions in various ways: (i) feedstock switch (avoidance
of the emission of a fossil CO2 current through its capture and utilization as input for urea
production) and (ii) thermal energy savings (through the reduction of fossil fuel combustion
needed to produce the CO2 input for urea production).
.........................................................
Although all these reactions represent interesting achievements, and good turnovers are reported
(Milstein and co-workers [56] showed turnover numbers up to 4400 h−1 under mild reaction
conditions; 10–60 atm H2 , 110–145◦ C, 1–14 h), the productivity (e.g. the tons of methanol of per h
and per reactor volume) is largely lower than that of conventional heterogeneous catalytic routes.
The exploitability of these discoveries to develop industrially competitive processes is thus still
to be verified. However, the many new proposed paths are indicative of the vitality of the topic.
Also in the area of the use of CO2 in organic synthesis, a number of recent breakthroughs
have been made; for example, in the area of carboxylation, the catalytic hydrocarboxylation of
styrene and the copper-catalysed hydrocarboxylation of alkynes using CO2 in the presence of a
hydrosilane [57]. These reactions open up new interesting perspectives for organic synthesis, but
all have low-volume productions. Therefore, they will not have a significant impact in shifting
chemical production to a low-carbon economy.
Electrocatalysis is offering new possibilities, either to produce small organic molecules to
be used in conjunction with or integrated into solar devices (for artificial leaf-type systems
[36–38]) or as a valuable synthetic procedure. The number of new discoveries after years
of stagnation is remarkable. There is the need to go beyond the conventional metal-type
electrodes operating in liquid phase. Gas-phase [58] or liquid-phase operations in the presence
of molecular catalysts (such as pyridinium ions) [59–62] are two promising directions to form
either methanol or even long-chain alcohols, but scientific effort in these areas is still too limited.
The use of non-conventional electrolytes, such as ionic liquids, is another attractive direction
[63,64]. New electrocatalysts have also been recently discovered; for example, a nanoporous
silver electrocatalyst that is able to electrochemically reduce CO2 to carbon monoxide with
approximately 92% selectivity at a rate over 3000 times higher than its polycrystalline counterpart
under moderate overpotentials of less than 0.50 V [65]. Electrocatalytic carbonylation on novel
catalysts (metal organic frameworks, e.g. [66]) is another interesting possibility (relevant for
organic syntheses).
This short panorama evidences that there are plenty of new ideas and emerging opportunities
in the area of CO2 (re)use, thus confirming that the CO2 challenge is not only relevant for industry
and society, but is an excellent opportunity to explore new concepts and new opportunities for
catalysis and industrial chemistry. However, many of the recent discoveries, particularly in the
area of homogeneous catalysis and electrocatalysis, have still to be proven to be exploitable at
the industrial level. Several of them appear to still have a productivity and cost-effectiveness
that are too low to consider industrial feasibility or aspects such as stability (particularly for
electrocatalysts) have still not been adequately investigated.
10
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
— frustrated Lewis pairs for homogeneous hydrogenation of CO2 [53,54];
— non-metal-mediated homogeneous hydrogenation of CO2 to CH3 OH [55]; and
— indirect conversion of CO2 to methanol based on the use of Ru pincer complexes as
catalysts for the hydrogenation of carbonates, carbamates and formats [56].
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
CO-dehydrogenase
3 CO2 + 8 H2
formate
2 [H] ATP, lHF
formyl-THF-synthase
formyl-THF+
H+
methenyl-THF-cyclohydrolase
methenyl-THF
[CO]
2 [H]
methylene-THF-dehydrogenase
acetogens
Wood–Ljungdahl pathway
(natural pathway)
synthetic pathway
acetone
HS-CoA
methylene-THF
2 [H]
methylene-THF-reductase
methyl-THF
Co-FeS-P
methyltransferase
H2O
acetyl-CoA
acetate
acetoacetate
methyl-TCo-FeS-P
HSCoA
CO-dehydrogenase/acetyl-CoA-synthase
acetyl-CoA
–HSCoA
acetoacetyl-CoA
Figure 4. Schematic mechanism, part natural and part synthetic, developed by Evonik to produce acetone from CO2 . (Adapted
from [68].) (Online version in colour.)
The synthesis of substituted ureas [67] is also of industrial interest, for their application in a
wide variety of fields, from refinery and petrochemicals to agrochemicals and pharmaceuticals.
Ureas are also useful in the production of carbamates. The use of CO2 as a starting material in
the synthesis of substituted ureas represents an intriguing alternative to classical phosgenation
methods and several possible approaches have been explored to date.
(f) Emerging opportunities for CO2 utilization: biotechnological routes
Bio-catalytic industrial routes for CO2 valorization represent an emerging opportunity. Evonik
is developing a CO2 -based acetone fermentation process using industrial waste-gas streams
that contain carbon monoxide (CO) and hydrogen (H2 ) in addition to CO2 . They use
genetically modified acetogens, e.g. bacteria strains (Clostridium ljungdahlii, C. carboxidivorans
and C. aceticum), that are able to utilize CO2 . The stage of development is the successful
production of acetone and its scale-up from flask into lab-fermenter. Figure 4 reports the schematic
mechanism, part natural and part synthetic, developed by Evonik to produce acetone from CO2
[68]. Evonik developed specific strains able to insert in the Wood–Ljungdahl natural pathway of
transformation, converting the intermediate acetyl-CoA into acetone.
Bio-succinic acid from glucose and CO2 is another interesting product derived from
engineering strategies [69,70]. At least five groups are developing (semi)commercial plants for
bio-succinic acid. Bioamber is starting a facility in Pomacle, France, with an annual capacity
of 2000 tonnes. Their process uses an Escherichia coli strain developed specifically to produce
succinic acid, with wheat-derived glucose currently being used as the substrate. DSM (now
Sabic) is also actively investigating the production of bio-succinic acid. In early 2008, DSM
formed a partnership with France’s Roquette Frères to develop bio-succinic acid, and the two
companies have been supplying kilo-scale samples for over a year from a pilot plant at Roquette’s
site (Lestrem, France). Myriant is building a commercial-scale facility in Louisiana, USA. The
company is currently making bio-succinic acid at the 20 000 litre bioreactor scale using E. coli and
unrefined sugar as a feedstock. BASF linked with Purac subsidiary CSM is planning to produce
bio-succinic acid using a BASF-developed bacterial strain (Basfi succiniproducens) and glycerine or
glucose as a feedstock. Finally, Mitsubishi Chemical Holdings Corporation has also developed its
own process for making bio-succinic acid from biomass.
.........................................................
CO2
2 [H]
formate-dehydrogenase
+ 5 H2O
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
C
ac O-d
ety eh
l-C ydr
oA oge
-sy na
nt se/
ha
se
11
genetically modified
CO
H2O
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
In a different approach, several purple non-sulfur bacteria were used to convert CO to H2 in
a process similar to the water gas shift (WGS) reaction. Lazarus et al. [76] reported the use of
redox enzymes on conducting graphite platelets to perform the WGS reaction efficiently at room
temperature. The H+ reduction reaction is catalysed by a hydrogenase, Hyd-2, from E. coli, and CO
oxidation is catalysed by a carbon monoxide dehydrogenase (CODH-I) from Carboxydothermus
hydrogenoformans. This system is claimed to have a turnover frequency (at 30◦ C about 2.5 s−1 per
minute functional unit, e.g. a CODH/Hyd-2 pair) comparable to conventional high-temperature
catalysts, although the productivity per reactor volume (the industrially relevant parameter) is
quite superior for the heterogeneous catalyst under optimized reaction conditions.
The following step of syngas fermentation is well established at the (semi)commercial level.
The production of fuels and chemicals through syngas fermentation offers some advantages over
metal catalytic conversion: the higher specificity of the biocatalyst, lower energy costs, greater
resistance to catalyst poisoning and independence of a fixed H2 : CO ratio. However, process
costs are still higher. There are several microorganisms which can produce fuels and chemicals by
.........................................................
— TiO2 nanoparticles modified by attachment of CODH and a Ru photosensitizer; this
system produces CO at a rate of 250 µmol of CO (g of TiO2 )−1 h−1 when illuminated
with visible light at pH 6 and 20◦ C.
— Assemblies of CODH with CdS nanocrystals; in this case, the CO production rate at best
is approximately 0.5 µmol h−1 , but the turnover frequency per enzyme molecule is better.
A total of 0.35 M 2-(N-morpholino)ethanesulfonic acid was used to buffer the acidifying
effect of CO2 in solution and to act as the electron donor.
12
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
Another interesting metabolic pathway is the production of longer chain alcohols from CO2 .
Mitsubishi Chemical Holdings Corporation is developing the original results of researchers at
the University of California, Los Angeles (UCLA) on CO2 conversion, in particular for the
production of butanol and hexanol by applying genetic manipulation techniques to modify
algae. Liao and co-workers [71] at UCLA developed engineered bacteria to convert CO2 into
alcohols, in particular genetically modified E. coli bacteria to produce various alcohols and
modified cyanobacterium to produce isobutanol. Using a non-natural metabolic engineering
approach, the branched-chain amino acid pathways are extended to produce abiotic longer
chain keto acids and alcohols by engineering the chain elongation activity of 2-isopropylmalate
synthase and altering the substrate specificity of downstream enzymes through rational protein
design [71]. When introduced into E. coli, this non-natural biosynthetic pathway produces
various long-chain alcohols with carbon number ranging from 5 to 8. The feasibility of this
approach was demonstrated by optimizing the biosynthesis of the 6-carbon alcohol, (S)-3methyl-1-pentanol. Later, the same group [72] showed the possibility of direct photosynthetic
recycling of CO2 to isobutyraldehyde. They have genetically engineered Synechococcus elongatus
PCC7942 to produce isobutyraldehyde and isobutanol directly from CO2 and increased
productivity by overexpression of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO).
Isobutyraldehyde is a precursor for the synthesis of other chemicals, and isobutanol can be
used as a gasoline substitute. The high vapour pressure of isobutyraldehyde allows in situ
product recovery and reduces product toxicity. The engineered strain remained active for 8 d and
produced isobutyraldehyde at a higher rate than those reported for ethanol, hydrogen or lipid
production by cyanobacteria or algae.
Rather interesting developments in biotech routes for CO2 valorization are also in the area of
syngas fermentation. Although industrial developments are still on the use of syngas (CO/H2 )
rather than CO2 , the modification of the path could lead to direct use of CO2 . It is known
that carbon monoxide dehydrogenase (CODH) from C. thermoaceticum (a Ni and Fe containing
metalloenzyme) catalyses the reversible oxidation of CO to CO2 . It is possible to couple this
enzyme with a semiconductor such as TiO2 , which produces the electrons necessary for the
reduction. A hybrid enzyme–nanoparticle system was used to achieve an efficient CO2 to CO
reduction using visible light as the energy source. Armstrong and co-workers [73–75] used
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
year
2000
2005
2010
2015
13
2020
2025
2030
light olefins
organic acids
bio-catalytic routes
thermochemical
electroreduction
photoreduction
artificial photosynthesis
demonstration
commercial (range of years when expected)
Figure 5. Estimated ‘technology roadmap’ for commercialization of CO2 reuse paths. (Online version in colour.)
syngas utilization. These microorganisms are mostly known as acetogens including C. ljungdahlii,
C. autoethanogenum, Eurobacterium limosum, etc. [77]. Most use the Wood–Ljungdahl pathway. The
fermentation of syngas to ethanol by C. ljungdahlii was developed into a commercial process that
combines biomass gasification, syngas fermentation and distillation of ethanol from the reactor
effluent. Syngas is cooled before it can be introduced into the bioreactor and is coupled to heat
recovery (BRI Energy; www.brienergy.com). The Lanzatech (www.lanzatech.com) process of CO
fermentation is currently applied on a 0.4 Ml demonstration facility (Shanghai, China) using steel
mill off-gas from a working steel mill [78]. INEOS Bio (www.ineosbio.com) also began in 2011
the construction of its first commercial-scale plant, the Indian River BioEnergy Center in Florida,
USA. Gas fermentation is thus an established technology, but clearly it would be interesting to
directly use CO2 along the lines outlined above. There are interesting scientific bases to develop
hybrid systems for this fascinating opportunity.
4. A technological roadmap for CO2 chemical utilization
The previous section gave a brief overview of the main aspects and tendencies for industrial
utilization of CO2 to develop new sustainable productions. As mentioned in the Introduction,
this interest is confirmed by the rising number of patents in this area and various new
companies created to find opportunities from this novel area of technology. A further important
aspect to consider is that the possible market for CO2 reuse is dependent on the possibility
of developing drop-in processes and products, because the cost for the introduction of new
technologies/processes is quite high. Different institutes have examined the possible scenario
and technology roadmap for the utilization of CO2 [79–84]. We feel, however, that the complexity
of the scenario was not always correctly identified, including the many socio-economic aspects
and the potential for technological development, market incentives and constraints (including
investment costs), etc.
Figure 5 reports our estimations for the ‘technology roadmap’ to commercialize CO2 reuse
paths. It was based on the above inputs, but was corrected by taking into account the results
of recent workshops, meetings, reports etc. as well as considerations regarding the possible
market, costs for implementation of the technology, perspectives in incentives on reuse of CO2
in relation to the different impact of the various technologies, drop-in characteristics of the
.........................................................
formic acid
formic acid as H2 vector
hydrocarb. (FT)
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
urea yield boosting
polymer
fine chem.
(org. synth.)
methanol
DME as RE vector
syngas
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
already industrial
EOR
4
4
3
3
4
4
3
3
3
3
2
4
4
3
2
2
2
3
1.5
3
2
3
3
4
4
4
potential development: 1, more than 10 years 4, industrial
external use of energy: 1, difficult to decrease 4, no need
time of sequestration: 1, very short 4, long term
2
not
known
2
1
4
4
2
4
1
1
4
2
2
4
2
1
1
1
4
3
3
electro photoelect
reduct. rochem.
bio
catal.
1
1
1
not
not
not
known known known
2
4
4
thermo
chem.
2
4
2
3
4
2
2
2
2
4
4
4
4
2
3
economic perspectives: 1, difficult to estimate
4, available industrial data
1, less than 10 Mton
4, more than 500 Mton
potential vol. of CO2:
4, low (solvents or toxic, metals resources)
other impacts on env.: 1, significant
Figure 6. Summary of the different options in the valorization of CO2 . (Adapted from [84].) (Online version in colour.)
technology/products, exploitability and technical constraints, etc. In figure 5, the light blue circle
represents technology at the pilot/demonstration scale, while the bar represents the expected
timeframe when commercial operation of the technology is likely. Owing to different uncertainties
in the conversion paths, the range of years when commercial operations will start changes from
path to path.
In terms of impact, the Parsons Brinckerhoff/Global CCS Institute [82] estimated that the main
path for CO2 use in 2020 will be non-chemical, e.g. by enhanced oil recovery (EOR), with a
cumulative demand (in year 2020) higher than 500 Mton and gross revenue higher than US$
7500 M. It should be commented, however, that EOR could not be properly considered a lowcarbon route because (i) EOR enhances the use of fossil fuels being used for oil displacement and
(ii) part of the CO2 used in EOR will be remitted owing to soil porosity.
A second main path will be related to urea yield boosting, mineral carbonation and enhanced
coal bed recovery with cumulative demand between 20 and 100 Mton and gross revenue
up to US$ 1500 M. For polymers, renewable methanol (RM), concrete curing, bauxite residue
carbonation and algae cultivation, the Parsons Brinckerhoff/Global CCS Institute [82] estimated
a cumulative demand between 5 and 20 Mton and gross revenue up to US$ 300 M. Formic acid
and enhanced geothermal systems account for less than 5 Mton cumulative demand and less than
US$ 75 M gross revenue (all referring to year 2020).
It should be noted that this scenario is strongly dependent on CO2 reuse as complementary
technology to CCS to favour legislative and regulatory regimes, as well as to accelerate CCS by
providing an economic driver. However, we feel that the potential for polymers and particularly
for RM (or DME) as vectors to transport RE as well as additive for fuels or to produce renewable
fuel components is not correctly estimated. The potential for CO2 as a C-source (in particular, for
producing light olefins) is also underestimated. A more correct estimation for these technologies
is that the cumulative demand to 2020 is at least 30–50 Mton with a gross revenue of up to US$
500–700 M, but it is expected to rapidly increase in the following decade.
It is worthwhile mentioning that the European Chemical Industry, through the SPIRE PPP
(Sustainable Process Industry Public–Private Partnership) initiative [85] and other relevant
documents [86], aims to reduce (by year 2030) fossil energy intensity by up to 30% and renewable
and primary raw material intensity by up to 20%. It is estimated that a significant part of these
targets (nearly half) could derive from CO2 valorization technologies.
(a) Assessing the different routes for CO2 utilization
The implementation of the different solutions will depend not only on techno-economic aspects
but also on other criteria. A comparison of the different routes, according to six criteria, is
14
.........................................................
4
long term
mineraliz
ation
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
potential
development
economic
perspectives
external use
of energy
potential vol.
of CO2
time of
sequestration
other impacts
on environment
medium term
short term
industrial organic hydrogena algae- reforming algae HC
use
synthesis
tion
open p.
reactor
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
(a)
(b)
aspirin
market value
reduction
storage lifetime
micro-algae
sustainable catalysts
market value
photocatalytic
thermochemical
plasma
sustainable feedstocks
time
development
growth
market capacity
CO2 reuse
(to chem./fuels)
maturity
decline
Figure 7. (a) Perspectives for enabling technologies in CO2 reuse (adapted from [81]) and (b) public perception of CO2 reuse
with respect to the case of aspirin and CCS [83]. (Online version in colour.)
presented in figure 6 [84]. These criteria allow a first quick overview of the degree of development
and the main issues of the various options to valorize CO2 . The criteria are the following.
(i) Potential development: this criterion indicates the length of time required to open the first
industrial facility. This duration depends on the R&D effort.
(ii) Economic perspectives: this criterion represents the prospect of achieving an economic
return. It also reflects the anticipated level of difficulty to remove economic blocks that
actually exist.
(iii) External use of energy: this criterion assesses the energy consumption per cost of the
product. This consumption takes into account energy requirements (electrical and
thermal) associated with the manufacture of the reagents (especially the production of
hydrogen or grinding of minerals) and energy requirements associated with processes.
The step to capture CO2 from industrial flue gases is not taken into account. Energy
consumption is a major issue, particularly for dry reforming and mineralization. Some
routes, such as microalgae or photo-electrocatalysis, present the significant advantage of
direct use of photons from the Sun and have little productivity cost depending on the
energy.
(iv) Potential volume of use of CO2 : this criterion represents the maximum amount of CO2
that could be potentially used—by year 2050—per year without any other consideration.
Emissions of CO2 released by the industrial process or during the use of the product are
not taken into account.
(v) Time of sequestration: related to the time of sequestration of CO2 before it is reintroduced
into the atmosphere.
(vi) Other environmental impacts: this criterion is related to the use of solvents or toxic
chemicals in the process, catalysts with negative impact on the environment and use of
scarce natural resources.
Figure 6 represents the visual summary of the indications given in the study by Thybaud & Lebain
[84] for the French Environment and Energy Management Agency, but some of their indications
may be questionable. For example, as remarked before, CO2 use for EOR cannot be properly
considered as a route for decreasing CO2 emissions, because the main effect is to stimulate a
larger use of fossil fuels.
.........................................................
catalysis
electrochemical
15
CCS
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
energy efficiency
net CO2 capture
10
9
8
7
6
5
4
3
2
1
0
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
(b) The perception of the role of CO2 utilization paths on the future of society
In order to complete the analysis of the technology roadmap in CO2 utilization technologies,
it is useful to analyse briefly the emerging patent literature trends, limited to the last 5 years
(2008–2013) and patents in English. The search was made with SciFinder as the main search
mechanism, using different keywords, based on the combination of CO2 and a second word from
the following list: (i) type of product (syngas, methanol, formic acid, urea, polymer, epoxide,
etc.), (ii) type of reaction (carboxylation, photo, electro, Fischer–Tropsch, plasma, reverse water
gas shift, etc.), (iii) company (Basf, Bayer, etc.), and (iv) generic (conversion, use, etc.). The entries
derived from these searches were then manually selected. In addition, the results were integrated
with additional searches using different patent databases: Google patents, USPTO, Patentdocs,
etc. In total, 230 entries were identified in the 2008–2013 period (year of publication of the patent)
relevant to the various sectors of CO2 catalytic conversion for chemical use.
.........................................................
(c) An analysis of emerging patent areas in relation to the technology roadmap
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
A proper analysis of the technology roadmap for CO2 utilization requires evaluation of the public
and industrial managers’ perception of the role of CO2 utilization paths on the future of society.
There are not many specific studies on these aspects, but the graphs reported in figure 7 are
useful to raise some relevant issues on this topic. The first graph [81] is the relation between
the stage of development and market value for some technologies of CO2 reuse, while the second
graph [83] reports a comparison of the public perception of CO2 reuse with respect to the case of
aspirin and CCS, according to seven key parameters. It is interesting to observe how, in terms of
public perception, CO2 reuse (for chemicals and/or fuels) is considered a largely more relevant
area with respect to carbon sequestration (CSS) and aspirin in terms of market capacity and
value, but a less relevant area for sustainable catalysts. The latter aspect is clearly connected
to poor public understanding of catalysis, because, for example, no catalysis at all is involved
in CO2 sequestration (thus questioning the impact on sustainable catalysts). Another interesting
result is that all three technologies are considered nearly equivalent in terms of net CO2 capture,
while CCS is considered much less energy efficient. CO2 reuse results are also better in terms
of sustainable feedstocks. On average, CO2 reuse is thus considered by the public as a positive
technology and better than CCS, favouring the social push to this technology as a significant
contribution to a low-carbon economy. However, the results in figure 7b also demonstrate the
need to raise awareness among general public of the methodologies of CO2 chemical utilization.
The results of figure 7a also provide some interesting, but questionable, aspects. Catalysis, for
example, is not a mature technology, at least in the aspects related to moving to a low-carbon
economy, realizing a more efficient use of resources and energy, and developing novel processes
for the use of renewables [87,88]. The market value and scientific maturity of electrochemical
technologies is definitively lower than that of catalytic reduction routes and not slightly superior,
as indicated in figure 7a. This figure is reproduced from a market study prepared by Frost &
Sullivan [81], which is a business consulting firm offering market analyses, research, etc. The
firm’s team consists of industry experts, consultants, market analysts and research executives.
The study is thus indicative of the perception of decision-makers on the economic potential of
CO2 utilization routes. Figure 7a and the cited report [81] indicate positive perspectives, but the
need to strengthen research. However, as commented above, there is still a lack of clarity on
research bottlenecks and effective impact. It is thus necessary from the scientific perspective to
increase effort not only to develop new scientific routes but also to effectively assess the issues
in moving from idea to innovation. In fact, only when enough critical mass of research effort
is dedicated to the topic of CO2 utilization will it be possible to translate to fact the technology
roadmap tentatively identified in figure 5. A combination of public and private funds is necessary
to reach this goal. From this perspective, it is important to mention that the cited SPIRE initiative
[85] is a public–private partnership, which has seen CO2 utilization as one of the pillars to move
to a sustainable, but competitive, future for the chemical industry.
16
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
11
17
8
1 CO2 to syngas
2 CO2 to methanol/DME
3 CO2 to formic acid
4 CO2 to acrylic acid and other acids
5 bio-catalytic routes in converting CO2
6 CO2 to olefins/hydrocarbons
7 CO2 use for organic syntheses
8 CO2 conversion to urea (advances)
9 CO2 use for monomers/polymers
10 CO2 conversion via photo/electro process
11 other approaches for CO2 conversion
7
6
5
4
3
2
1
0
10
20
30
no. patents
40
50
60
Figure 8. Number of patents identified in the period 2008–2013 for the catalytic processes of CO2 conversion to chemicals,
classified according to 11 main classes of reactions. (Online version in colour.)
It must be noted that the patents identified included only those where the use of CO2 was
a key element. For example, the patents for methanol or Fischer–Tropsch synthesis typically
report the use of syngas as feedstock, and also indicate the possible presence of CO2 in the
feed. These patents were not considered here because the catalysts for using pure CO2 (+H2 )
are different from those using syngas (CO + H2 ) or syngas containing small amounts (typically
less 4%) of CO2 .
The patents identified were all classified according to 11 main classes of reactions. The results
are summarized in figure 8. The three top areas in terms of number of patents are the conversion of
CO2 to syngas, the use of CO2 for monomers/polymers and the photo/electrocatalytic processes
for using CO2 . It should also be noted that the total number of patents appears to be limited.
There are various reasons for this:
— there is a delay between scientific interest and the exploitation of the results;
— large companies still need to define their priorities in this area, and for this reason there
is a delay in patents;
— small companies in some cases use patents as a way to increase visibility, but in several
cases prefer to avoid patenting to avoid disseminating information.
The trend in the number of patents in the last 5 years, however, clearly shows that up to about
2010 the number of identified patents in this area was nearly constant (approx. 15–20 per year), but
then rapidly rose to reach approximately 130 patents in 2013. This result confirms the suggestion
that it is only very recently that companies are looking more seriously at this area as a potential
business area.
(d) Indications from the technology roadmap
We conclude this section on the technology roadmap for CO2 utilization by indicating that the
area of CO2 chemical utilization shows several topics of industrial interest, characterized by the
different stages of development in the technology roadmap (figure 5). A significant gap exists
between the stage of R&D development reported in the open literature, and the innovation and
technology chain represented by patenting activity. This is an area in which patent activity is still
significantly behind R&D. Several large companies need to fully develop their business strategies
in this area, often delayed because of slow recognition of the potential, while start-up/venture
capital companies have a more aggressive patenting policy. However, the assessment of the
patents reveals how often patents have claimed system approaches (process or device design,
often also based on established state of the art) rather than specific breakthroughs and discoveries.
.........................................................
9
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
area of CO2 utilization
10
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
— all these RE sources produce electrical energy as the output, while direct use of electrical
energy in the actual chemical production accounts for only a small fraction (10–15%
typically) of the energy input;
— these RE sources are discontinuous, while a continuous input is necessary in process and
chemical industries.
The reaction of CO2 catalytic hydrogenation to methanol with renewable H2 (as mentioned
before, we focus discussion here on this reaction [7,27,31], but other products may also potentially
be exploited) solves both these issues, because it forms:
— a chemical, which may be introduced directly in the chemical production chain or after
the eventual conversion to other building blocks for petrochemistry (light olefins, e.g.
[46]); also note that these are products already in widespread use (drop-in products) and
do not require large investments for their use differently from novel chemicals;
— a liquid product, which can be easily stored and distributed, bypassing the issue of RE
production intermittency (this means that it may also be possible to use unexploited
remote sources or excess of RE production; both of these are current relevant targets for
R&D in the area of RE).
The advantage of short life cycles (for example, when converting CO2 to ‘solar’ fuels) in contrast
to long-term storage of CO2 has been discussed above, but it may be useful to remark that the
value of merit is related to enhancing the introduction of low-carbon energy in the energy value
chain, rather than ’storing’ CO2 . From this perspective, it is not relevant from which source the
CO2 derives. The perspective should thus be shifted from a direct reduction of CO2 emissions by
storage to the different, and more interesting, perspective of how the reuse of CO2 contributes to
enabling the new low-carbon economy.
With respect to bio-routes, CO2 utilization paths are not in opposition, but in integration to
move to a low-carbon economy [31–33]. Realizing a sustainable, resource-efficient and low-carbon
economy requires integrating in the chemical production chain other forms of RE than those
associated with the use of biomass. This emerges from the analysis of the different scenarios for
a bio-based economy [89,90], taking into account the social and techno-economic constraints in
developing some of the routes. In other words, it is necessary to analyse the integration of RE
sources (solar, wind, hydro, etc.) in the chemical production chain along the lines indicated above.
A relevant question also regards the cost-effectiveness of the bio-based versus CO2 -based
routes, although it is relevant to mention how a more specific analysis (case by case) would be
necessary. In general terms, biofuel production and consumption have been expanded not in
response to market forces, but rather to comply with government policies (for example, mandate
in using biofuels). On average, the use of bioenergy allows a saving of approximately 50% of CO2
emissions with respect to fossil fuels. This is an average value because many parameters affect
LCA of the use of bioenergy [91,92]. Methanol produced from the reuse of CO2 and RE has a
potentially larger impact in terms of saving CO2 emissions, as well as in terms of resource and
energy efficiency. CO2 chemical utilization to make (renewable) methanol, for example, has many
advantages:
.........................................................
Moving to a resource- and energy-efficient chemical production requires finding effective ways to
introduce renewable resources into the chemical production chain. There are two main possible
routes to introduce RE in the process and chemical industries: (i) an indirect path via biomass and
(ii) a direct use of RE sources such as solar, wind, hydro, etc. However, the latter path suffers from
two main drawbacks:
18
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
5. Introducing renewable energy in the chemical production chain through CO2
utilization
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
pure (>99%) CO2 stream
19
recycle
O2
transport
H2
H2O
electrical
energy
vent
CH3OH
H2O
Figure 9. Simplified block diagram of different material flows participating in the process of methanol synthesis from CO2 and
renewable H2 . (Adapted from [27].) (Online version in colour.)
— The CO2 to (renewable) methanol (and back to CO2 during methanol use) has a shorttime cycle; at each cycle, RE (used to produce the H2 needed for the reaction) inserts
RE in the energy/chemical system. Over a certain period (20 years, for example) each
recycled CO2 molecule saves CO2 equivalent emissions corresponding to how many
times the cycle is repeated multiplied by the effective energy introduced in the system,
after subtracting the energy necessary to perform the cycle. While the effectiveness factor
for geological storage of CO2 is approximately 0.5 (considering the energy to capture and
store CO2 ), this factor is over 10–20 for CO2 reuse incorporating RE in the conversion
process [93].
— Trading RE through the conversion of CO2 contributes to energy security, by diversifying
the sources and valorizing local production.
— The chemical utilization of CO2 improves innovation in industry, preserving
competiveness and jobs.
Another key question regards the economic sustainability of the route. Current methanol
production from CO2 and renewable H2 involves a process based on multiple steps (figure 9).
— Electrical energy can be produced by different routes (hydro, solar, wind, etc.), but we
consider here especially hydropower in remote (underexploited or unexploited) areas for
the motivations discussed later.
— The (renewable) electrical energy is used in a water electrolyser, preferably operating at
high pressure (greater than 30 bars). This is currently the state-of-the-art technology to
produce H2 by electrolysis, but there are fast and interesting developments in solid oxide
electrolyser cells (SOECs) [94–96], indicating that this technology is promising for the
future. It is also possible to co-electrolyse CO2 and H2 to produce syngas, which can be
fed directly to a conventional methanol synthesis route [97,98]. However, costs are still
high [98] and a single unit does not produce the necessary H2 /CO ratio for feeding to the
methanol unit.
— Renewable H2 and CO2 are then fed to a catalytic unit to synthetize methanol. It may be a
single unit or two units (RWGS first and then methanol synthesis unit, with intermediate
removal of water formed in the first step). By using suitable catalysts and reaction
conditions, other chemicals (light olefins) and fuels (DME, methane, higher hydrocarbons
or alcohols, etc.) could alternatively be produced.
The concept of using the conversion of CO2 to methanol to import RE to Europe (as an example)
from remote unexploited areas is schematically presented in figure 10. The technology can be
.........................................................
CO2
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
CO2 recovery units
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
20
remote areas
(no local use, far from grid)
CO2
–500
catalyst
CH3OH
–400
–300
DH° (kJ mol–1)
–200
Figure 10. Concept of using the reaction of CO2 conversion to methanol to import RE to Europe (as an example) from remote
unexploited areas. (Online version in colour.)
400
methanol production cost ( /ton)
375
350
renewable H2 production cost
sensitivity analysis:
1, cost CO2 at site: 20–70 /ton CH3OH
2, electricity consumption for H2 prod.:
3.8 – 4.8 kWh/Nm3 H2
0.140
Nm–3 H2
variability in
production costs
325
300
1
2
275
250
225
200
using rH2
conventional
Figure 11. Comparison of the methanol production cost from CO2 and renewable H2 with respect to the conventional production
cost from fossil fuels (average cost estimated for Europe, methanol plant capacity of 2400 ton d−1 ; typical fluctuation range in
production costs is also indicated). For the production cost using renewable H2 (methanol plant capacity of 2400 ton d−1 ), the
variability in production costs depending on the cost of CO2 at site and the electricity consumption for H2 production is also
shown. (Elaborated from the data reported in [27].) (Online version in colour.)
considered nearly ready for commercialization, although scale-up aspects in electrolysers have to
be solved and improvements in CO2 conversion catalysts and in the stability of the electrolysers,
particularly under high-pressure operations, would be necessary [7,27]. In the longer term
(approx. 15 years), it will be possible to reduce the number of steps, realizing inverse fuel cells
or directly solar fuel cells [37–39,99–101].
A techno-economic evaluation of this possibility [27] showed that methanol can be produced
by this route at a cost that is competitive with conventional methanol production from fossil fuels
(comparison made for a methanol plant with a capacity of 2400 tons per day, corresponding to
one GWh hydropower plant). Figure 11 summarizes some of the key results, as well as some
elements of the sensitivity analysis for the production cost using renewable H2 (other elements of
.........................................................
H2
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
RE-based fuel
renewable
H2
–
e
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
This document evidenced that making methanol from CO2 /renewable H2 is a key priority for
Europe and the need for specific research to enable this route.
(a) Advantages of producing renewable methanol
Methanol from CO2 /rH2 is a renewable fuel as established by the Renewable Energy Directives of
the European Union. We use here the term ‘renewable methanol’ to indicate methanol synthesized
from CO2 and H2 , the latter produced using only RE sources, by either electrolysis or other
methodologies (bio-routes, solar thermal, using semiconductor photocatalysts, etc. [39]). While,
in principle, the indication ‘renewable methanol’ should also be applied when CO2 is not derived
from fossil sources, we do not apply this restricted interpretation here because, as commented in
the previous sections, the true value of converting CO2 to fuels (methanol, but also other energy
vectors such as methane) is not related to the sequestration of CO2 itself (which is negligible in
the case of fuels, because of their short life cycle), but to their enabling effect in introducing more
low-carbon energy sources in the energy (or chemical) value chain.
The same conceptual scheme may be used (i) to produce different types of products (either
fuels such as hydrocarbons, higher alcohols, DME, or chemicals such as light olefins, etc.) and
(ii) to exploit other sources of RE than hydropower (solar, wind, geothermal, etc.). However, we
believe that the combination of methanol and hydropower is a better initial choice to develop the
technology for the following reasons.
— Methanol, in comparison with other solutions (such as FT hydrocarbons), has the
advantage of less complex process technology, higher selectivity and flexibility in use;
methanol is compatible with transport back on ships transporting CO2 , thus reducing
transport costs; transport costs were included in the cited evaluation of costs of producing
RM in remote areas [27].
.........................................................
— the benefits in terms of reduced dependence on conventional fossil fuels and lower risks
to security of supply for this solution;
— how this solution would be attractive not only for the transport sector but also for other
industries;
— how Europe’s increasingly limited and expensive access to fossil fuels makes it obligatory
to consider policy options and smart strategies, combining market, regulatory and
planning instruments to bring down the direct and indirect costs of alternative fuels, so
that transport services remain affordable for citizens and companies during the transition
to a less petroleum-dependent economy.
21
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
sensitivity analysis and full details on techno-economic estimation are reported in [27]) and the
variability in average costs for the production of methanol in Europe from fossil fuels (methane)
for a comparable plant capacity. In remote areas, electricity from hydropower plants could be
produced at rather low costs, giving rise to low renewable H2 production cost (on average
about 0.140A
C Nm−3 H2 with current electrolyser technology). With these costs, it is convenient
to produce RM rather than from fossil fuels, enabling a range of applications, from direct use of
methanol as a feedstock for the chemical industry (to produce light olefins, for example) to using
methanol as an energy carrier for chemical production, in addition to various uses of methanol
in transport applications. Edwards and co-workers [102] in collaboration with Lotus Engineering
(UK), PARC (Palo Alto, CA), FSK Technology (UK) and GT-Systems (UK) presented a similar
concept of methanol as a versatile energy carrier produced by recycling CO2 and combining it
with renewable H2 . They remarked how the synthesis and storage of carbon-neutral liquid fuels
offers the possibility of decarbonizing transport without the paradigm shifts required by either
electrification of the vehicle fleet or conversion to a hydrogen economy.
A recent study by the Science and Technology Options Assessment of the European Parliament
[103] on methanol as a future transport fuel based on H2 and CO2 showed
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
— RM has a diversified market and use:
(b) Potential sources of unexploited renewable energy
There is a large untapped hydropower potential. The global technically exploitable hydropower
potential is estimated as approximately 16.4 PWh per year, e.g. over 80% of the unexploited
potential [106]. A large part of this potential can be utilized only when effective ways to transport
this RE over long distances (more than 500 km) are developed.
There is thus a large potential for increasing hydropower production by constructing dams
in various remote areas, when effective technology to transport this RE over long distances is
developed. This solution offers the great opportunity to combine a cost-effective increase in
generation capacity with the diversification of energy sources and thus better energy security.
With respect to alternative RE sources, hydropower shows distinct advantages: (i) it is still the
cheapest production of RE on a large scale, (ii) it is a readily available technology, and (iii)
it provides nearly a constant supply, while most of alternative RE sources (wind, solar, etc.)
are discontinuous. The last aspect means that the fixed costs of the technology for converting
electrical energy to chemical energy (methanol), as examined in depth below, can be amortized
over the whole year, whereas this is possible for only a fraction of time for discontinuous sources
of RE such as wind and solar. This is a key economic element for costs. There are some concerns
regarding the environmental impact of hydropower, but there is a general consensus that it is
among the cleaner technologies to produce energy.
The exploitation of hydropower untapped sources in remote areas is thus the preferable option
in the initial stage of introduction of the proposed technology.
.........................................................
Methanol turbines have been demonstrated on pilot units to have low NOx emissions. For
example, GE tested a MS6001B full-scale combustor representative of GE heavy-duty gas turbine
combustors and an MS7001 developmental dry low-NOx combustor. The tests demonstrated
that methanol fuel can be successfully burned in GE heavy-duty combustors without requiring
major modifications to the combustor, and NOx emissions were approximately 20% lower. Other
pilot unit tests showed that methanol-fuelled turbines reduce NOx emissions by 30% with
respect to using methane as the feedstock [104]. Water content in the methanol provides further
NOx reduction.
The use of methanol-fuelled gas turbines allows high efficiencies of over 60% to be obtained
(in particular, by using combined cycle systems with/without CO2 capture based on methanol
indirect combustion or solid oxide fuel cell combined with a gas turbine (SOFC-GT) hybrid
systems [105]) together with recovery of CO2 . In this way, an efficient closed-loop system for
importing RE from remote areas will be possible.
22
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
(a) it can be mixed (directly or after conversion to DME) with biofuels to reach
renewable standards and/or can be used as a raw material to produce various
additives for fuels (MTBE, as an example, which can be produced from isobutene
and methanol; when both derive from renewable sources—isobutene could be
produced from biomass—this is a high octane number component for gasoline; thus
a great and boosting synergy with biofuels to meet European Union targets on RE
and GHG reduction);
(b) it is a raw material for the process industry; for example, it may be used for
producing the building blocks for petrochemical production, e.g. olefins, besides
various other uses. In this way, methanol can contribute significantly to reaching
low-carbon production targets in this sector, but also has a diversified and higher
added value market;
(c) methanol allows a better flexibility in energy management to follow fluctuating
energy demand, because, for example, methanol-fuelled turbines have a rapid
switch off–on time. Methanol is a superior turbine fuel, with low emissions, excellent
heat rate and high power output.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Table 1. Estimation for Europe by 2050 of the potential contribution to the reduction of CO2 emissions by CCS, use of biofuels
and CO2 /renewable H2 to CH3 OH. (Adapted from [27].)
CCS
600
60
use of biofuels
700
35
CO2 /rH2 to CH3 OH
800
20
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
..........................................................................................................................................................................................................
In addition to exploiting unused hydropower resources, deserts and arid regions offer also a
large, unexploited potential for large-scale generation of RE (photovoltaics (PV), wind) which can
be effectively exploited only when the problem of transporting the produced electrical energy
over long distances is solved. The cost of the production of electrical energy by wind and by solar
PV panels is rapidly falling and in desert/arid areas, where the density of population and fauna
is limited, the impact on the land and environment is reduced. Finally, the conversion of electrical
to chemical energy, by synthesizing liquid energy vectors such as methanol, allows the issue of
intermittency in energy generation by wind and solar PV panels to be solved. The potential of
wind and solar energy production costing less than 50A
C MWh−1 (in 2050) was estimated to be
over 10 PWh [107].
Assuming that only a part of this potential RE can be exploited, there is still a potential of over
10 PWh yr−1 of electrical energy which can be produced from unexploited renewable sources and
whose use can significantly move the chemical industry towards low-carbon production.
(c) Impact on ecosystem and potential contribution to climate change control
Ten petawatt hours per year of electrical energy corresponds to a reduction of approximately
7 Gtons of CO2 equivalent emissions. In order to assess the relevance of this potential contribution
to CO2 mitigation strategies, it is necessary to start with the Blue Map Scenario of the International
Energy Agency (IEA) [108] for 2050 that CCS will remove about 8 Gtons of CO2 . However,
the effective contribution (by taking into account the energy requirement for CO2 capture and
storage) will be nearly half. The conversion of CO2 to methanol using renewable H2 , in order to
use unexploited RE sources, will thus have a better impact than CCS in contributing to climate
change mitigation.
Table 1 reports the estimate for Europe by 2050 of the potential contribution to the reduction
of CO2 emissions [27] by
— CCS (not considering the energy needed for CO2 capture, transport and storage; the
effective contribution will thus be lower);
— use of biofuels (average contribution, not considering land change use and other aspects
such as intensified GHG emissions due to enhanced use of fertilizers consequent to
monocultures);
— importing RE via conversion of CO2 to methanol (CO2 /rH2 to CH3 OH). In the latter
case, this was based on considering 15% of unexploited RE, and includes about 0.2 tons
CO2 per ton of avoided CO2 eq. emissions owing to the energy needs for conversion to
methanol and transport. The impact avoids CO2 emissions by introducing RE into the
energy chain.
Table 1 also compares the estimated cost (in 2050) per 1 Gton CO2 removed in these three cases
[27]. The cost for CCS was based on the estimated average cost of capture and storage of CO2 ,
while the cost for biofuels was based on the data from the IEA (Blue Map Scenario) [108] for the
incremental costs for biofuels (approx. US$ 330 billion in the high-cost scenario, with oil estimated
.........................................................
estimated cost per
1 Gton CO2 eq. removed (BA
C)
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
potential contribution to reduction of
GHG emissions (Mton CO2 eq.)
23
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
(d) Methanol uses and market perspectives
Methanol serves three key markets: chemicals, transportation and power generation. The
dynamics of RM in each of these markets will depend on their respective demand and
prices. Market segments that offer an advantage for RM, such as transportation and electricity
generation, are more likely to see RM use. An estimated total of approximately 65 million tons
of methanol and its derivatives are used annually in the world (in 2013), and China is on track
to become the world’s leading methanol market. The chemicals market represents the traditional
market of methanol, but energy uses are fast growing. Over one-third of the actual production
is for energy use and is rapidly increasing, particularly in Asia. In China, petrol is mixed with
methanol (15%) without the need for engines to be redesigned.
The uses of methanol are showing rapid growth, with world demand increasing from
approximately 65 Mtons in 2013 to approximately 95 Mtons in 2016, driven by both energy uses
and the production of olefins. The operating rate, e.g. plant capacity utilization rate, is expected
to increase to approximately 70% (in 2013) to over 80% (in 2016). This indicates that there will be
a progressive shortage in supply versus demand, with a consequent increase in the prices, higher
in regions such as Europe and China, which are net importers of methanol [109]. Indications for
Europe (and also China) are that this deficit of local production will increase in coming years.
The net import of methanol in Europe is expected to increase from approximately 4150 to 5250
thousand metric tons between 2011 and 2016 [109]. In addition, the expected trends in average
industry spot prices for methanol are significantly increasing in coming years. These results
indicate that there exists a need and demand in Europe for an alternative production of RM and
the economic perspectives in terms of prices are rather positive.
6. CO2 : a suitable C-source to move to a low-carbon chemical production
CO2 has many possible uses to move to a low-carbon chemical production, but there will be
a higher impact when basic raw materials (light olefins, syngas; as outlined in figure 2) are
produced from CO2 .
(a) Syngas production from CO2
Syngas is one of the major
over 70 000 MWth, currently
by petroleum (including fuel
capacity, covering 56 plants
base chemicals produced worldwide, with a 2010 capacity of
derived as approximately 51% (53 plants) from coal, followed
oil, refinery residue and naphtha) with 25% of total gasification
[110]. NG provides 22%, with petcoke approximately 1% and
.........................................................
— reduced emissions of pollutants (NOx, etc.) and GHG emissions, because the use of
unexploited RE sources reduces the need for new power plants as well as for extraction
of fossil fuels;
— better diversification of energy resources (with benefits in terms of energy security) and
greater flexibility in use (methanol or DME can be used to produce components for the
transport sector, for example);
— better flexibility in energy management to follow fluctuating energy demand, because,
for example, methanol-fuelled turbines have a rapid switch off–on time. Methanol is
considered a superior turbine fuel, with low emissions, excellent heat rate and high power
output, as indicated before.
24
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
at US$ 120 per bbl in 2050). The cost for the CO2 /rH2 to CH3 OH case was based on considering
20A
C per ton subsidies (related to avoided carbon taxes) to make the methanol cost equivalent to
the fuel projected cost. Table 1 shows that the proposed technology (CO2 /rH2 to CH3 OH) is a
cost-effective solution for GHG emission reduction and environmentally a more effective path for
the following reasons:
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
Given that RWGS is a reversible reaction, catalysts active in the direct WGS reaction are also active
in the reverse reaction. Different classes of catalysts have been studied for this reaction:
— Copper-based catalysts, particularly CuO/ZnO oxides, modified by alumina, zirconia,
titania and/or silica. Cu–ZnO based catalysts suffer from the drawback of being
pyrophoric and highly susceptible to poisons.
— Iron-based catalysts, essentially modifications of the commercial high-temperature Fe–
Cr catalyst. Iron-based catalysts require reaction temperatures above 400◦ C and are not
suited for RWGS reactions.
— Cerium oxide-based catalysts. Most of the studies on cerium-based catalysts have been
focused on noble metals (Pt mainly) supported on cerium. Other catalysts studied
include ruthenium and iridium-based catalysts (supported over various oxides), goldbased catalysts (particularly Au/Fe2 O3 and Au/TiO2 ) and nickel-based catalysts (e.g.
Ni–Ce(La)Ox).
A review by Polychronopoulou et al. [112] provides an overview of the use of cerium-based
catalytic materials with a focus on representative patenting activities in the past 10 years.
For the specific use in RWGS reactions, particularly when coupled with integrated methanol
production, Cu–ZnO/Al2 O3 -based catalysts are preferable or Pt or Au supported on CeO2 , when
a lower temperature activity is needed. Still debate exists about the reaction mechanism in RWGS
reactions.
There are other possible routes for producing CO or syngas from CO2 using renewable sources
of energy, in addition to the catalytic RWGS using H2 produced from RE sources (solar, wind,
hydropower, etc.), although we do not discuss them in detail here:
— thermo-catalytic (solar-assisted) routes, where the Sun is essentially used to produce the
heat of reaction necessary for endothermic processes (e.g. CO2 reforming) or to reduce
metal oxide materials which are then re-oxidized by CO2 ;
.........................................................
— Increasing the CO2 concentration to force the complete consumption of H2 , then recycling
the excess CO2 in the exhaust stream back into the reactor.
— Operating at high H2 concentration to force the complete consumption of the CO2 , then
recycling the excess H2 back into the reactor.
— Removing water vapour from the reactor, thereby driving the reaction to the right. Such a
system could be realized either with a desiccant bed or with a water permeoselective
membrane. Various studies have been reported recently on membrane application in
FT synthesis reactors [111], where silico-alumina or zeolitic membranes are used for the
selective removal of the by-product H2 O, which deactivates FT catalysts and inhibits the
reaction rate. The same concept could be applied for shifting the equilibrium in a RWGS
reaction.
25
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
biomass/waste accounting for 0.5%. About 45% of the overall syngas production is used to
produce chemicals, while 38% is used for producing liquid fuels. Chemicals are generated at
112 plants and liquid transportation fuels at five plants. Other products are power (11%) and
gaseous fuels (6%). There is thus a potential large market for producing syngas from non-fossil
fuel resources, in particular CO2 .
The catalytic RWGS reaction using rH2 is the main route to produce syngas from CO2 . This is
a mildly endothermic reaction with enthalpy and free energy changes of H298K = 41.2 kJ mol−1
and G298K = 28.6 kJ mol−1 , respectively. The reaction has been known for over two centuries,
but there is still the need to develop improved catalysts, as, for example, iron–chromium catalysts
are active at temperatures of 400◦ C or greater, but at this temperature the equilibrium constant,
Kp, is low and it is not possible to drive the RWGS reaction to completion. The equilibrium can
be shifted to the right by different options:
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
new
catalysts
(FT-type)
multifunctional
catalysts
H2
H2
methanol
catalyst
CH3OH
(DME)
–H2O
H2
acid
catalysts
modified
FT
catalysts
MTO
(zeolite)
C2-C3 olefins
–H2O
Figure 12. Different routes to synthesize light olefins from CO2 and renewable H2 . (Adapted from [7,46].) (Online version in
colour.)
— electro- or photocatalysis, where RE sources produce electricity that is then used in the
electro-driven process, or solar light (photons) is directly used;
— plasma processes, where RE produces the electrical energy to drive the plasma
generation;
— bio-processes, e.g. by hybrid enzyme–nanoparticle systems, bioelectrochemical reduction
or using a biomass char and catalyst such as Ni/Al2 O3 ; in these cases, either photons or
electrons (the latter generated by RE sources) are used. When using biomass char as the
reducing agent, this reactant can be considered renewable. Some other aspects of bioroutes to produce syngas from CO2 have been mentioned above.
Another interesting area that is growing in importance is high-temperature (in SOEC devices
mentioned earlier) ’co-electrolysis’ of CO2 and steam to produce syngas (CO + H2 ). The
long-term operation of cells indicates a long lifetime (up to over 10 000–20 000 h [113]). Technoeconomic estimations [114] indicate that, although not yet technologically mature, the hightemperature steam/CO2 co-electrolysis process is a feasible and environmentally benign route.
As an energy-intensive process, the availability of cost-effective electricity is crucial for its
economic competitiveness. Graves et al. [115] indicated that high-temperature co-electrolysis of
H2 O and CO2 makes very efficient use of electricity and heat (near-100% electricity-to-syngas
efficiency, but only when full heat integration is present, a rather difficult practical case), provides
high reaction rates, and directly produces syngas (CO/H2 mixtures) for use in conventional
catalytic fuel synthesis reactors. A target for the competitiveness of the process is electricity at
4–5 US cents kWh−1 , which is in line with the case discussed for methanol synthesis. SOEC and
co-electrolysis are part of the Danish vision to reach a fossil-free economy by 2050.
(b) Light olefins production from CO2
Light olefins (ethylene and propylene) can be produced from different sources, the main processes
being the steam cracking of oil or natural gas fractions, while direct dehydrogenation of alkanes
accounts for only a few per cent of the overall production [46]. New process routes include the
dehydration of ethanol deriving from biomass fermentation and production via syngas (through
the intermediate synthesis of methanol) from coal combustion or biomass pyrolysis/gasification
[32]. The use of CO2 is a new interesting option to produce light olefins, which have been shown
to be economically valuable, when renewable H2 could be produced at low costs, below about
US$1–2 per kg [46].
There are different possible routes to produce light olefins from CO2 and renewable H2
(figure 12). Being promoted by the same catalysts of further conversion, RWGS is typically
present. Direct routes converting CO2 not involving the intermediate reversible reaction of RWGS
.........................................................
–H2O
26
removal
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
renewable H2O
energy
RWGS
CO2 + H2
CO2 + H2O
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
The utilization of CO2 as a feedstock for producing chemicals is an interesting challenge to
explore new concepts and new opportunities for catalysis and industrial chemistry. It is an
excellent possibility to inject RE in the energy or chemical production chains. The latter is a
major problem facing the chemical industry to increase its efficiency in the use of resources and
energy. However, a major hurdle is the development of cheaper production of renewable H2 by
improving electrocatalysts and device technology in the current electrolysers (and in the long
.........................................................
7. Conclusion
27
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
would be preferable to overcome thermodynamic constraints related to this equilibrium reaction.
Light olefins could be directly produced from syngas (CO + H2 ), using modified FT catalysts,
or indirectly, via the formation of methanol (using conventional commercial methanol catalysts)
and then converting methanol to light olefins using the methanol to olefins (MTO) process based
on small-pore zeolites. In the presence of an acid catalyst, two methanol molecules could be
dehydrated to DME, which can also be converted to light olefins (it is an intermediate in the
process).
The methanol catalysts are active also in the RWGS reaction and thus the two steps can be
combined, but the water produced in the reaction inhibits the reaction rate and should thus
preferably be removed in situ. It is also possible to combine the catalysts for methanol with the
zeolite for MTO to have in one step the direct formation of light olefins from CO2 and H2 .
The route for light olefins from CO2 + H2 via syngas and then modified FT catalysts is
potentially simpler, but gives rise to a broader distribution of olefins. The route passing through
methanol/DME and MTO/MTP processes is more complex, but it is based on already established
catalysts/processes, whose economics are interesting for large-scale plants. The use of CO2 + H2
instead of syngas causes lower rates and selectivities in both cases. It would thus be necessary to
develop novel and specific catalysts. They should be designed to contain selective sites for direct
light olefin production by hydrogenation of CO2 .
An interesting route, still largely unexplored, involves the possibility of having a mixed
mechanism between that present in methanol synthesis [116], leading to the formation of formate
(HCOO) surface species from chemisorbed CO2 and H, and that for the FT reaction, with a key
step of C−C bond formation between the surface formate and ‘C1’ type species deriving from CO
dissociation. A similar mechanism was proposed originally by Izumi [117] to explain the selective
synthesis of ethanol from CO2 + H2 on [Rh10 Se]/TiO2 catalysts. Rh/SiO2 and Rh–Fe/SiO2 are
active in the hydrogenation of CO2 to ethanol, although selectivities to ethanol are 30% at best. In
CO2 hydrogenation over supported [Rh10 Se] clusters, selectivity up to over 80% was observed,
even if the conversion was not given. The ethanol may then be easily dehydrated selectively to
form ethylene.
A new route was proposed recently by Ogura [118] based on the electrochemical
conversion of CO2 using Cu electrodes and rather specific conditions involving a three-phase
(gas/solution/solid) interface, concentrated solution of potassium halide, low pH and copper or
Cu(I) halide-confined metal electrode.
In general, the electrocatalytic reduction of CO2 is attractive, but productivity is low, selectivity
has to be improved (approx. 60% at the best), high potentials (−2.4 V versus Ag/AgCl) are
required and stability is to be verified. A necessary condition to exploit electrocatalytic conversion
of CO2 on an industrial scale is to develop higher surface area (three-dimensional type) efficient
electrodes. The heterogeneous catalysis approach, even if it also has to be improved, is currently
preferable. All catalysts tested are based on catalysts for syngas (CO/H2 ) adapted to operate with
CO2 and H2 , but not specifically developed to work with CO2 .
Although further improvements in catalysts, reactor design and process operations are
necessary, these results show that it should be possible to modify FT or methanol catalysts to
selectively form light olefins, or even develop new types of catalysts based on a novel reaction
scheme. It is reasonable to consider a further optimization with a target in selective synthesis of
light olefins of over 80% at higher productivity.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
28
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
term, integrating this step in a CO2 conversion device). When rather cheap electrical energy from
renewable sources is available, the use of CO2 may already be economic.
In terms of the potential for application, the catalytic hydrogenation of CO2 to methanol
appears to have the highest maturity for commercialization. It may be already commercially
interesting when cheap sources of renewable H2 are available or when it may be used to store an
excess of electrical energy. It may be estimated that this reaction could reach the industrial stage
in less than 5 years. This development would be pushed by experience in pilot or pre-commercial
industrial plants, such as the discussed Mitsui plant (pilot in Japan, and large unit expected in
Singapore) and methanol plant in Iceland (Carbon Recycling Inc.). Methanol can be used both as
a chemical (directly or as an intermediate for other products, including light olefins) and as a fuel
(directly, or to produce fuel additives/components).
Many new routes are also explored for activating CO2 by homogeneous routes, as discussed
in §3.4. Although scientifically attractive, none of them appear to be industrially competitive. An
alternative route recently proposed for the indirect conversion of CO2 to methanol is based on
the use of Ru pincer complexes as catalysts for the hydrogenation of carbonates, carbamates and
formates. Although this reaction shows many attractive features (atom-economy and operates
in the absence of solvent with good turnover numbers), the industrial exploitability has to be
verified. It has been remarked how productivity rather than turnover is the parameter to consider
for industrial exploitability.
There is a lot of interest in the development of new modified FT catalysts for selective
light olefins synthesis from CO2 , preferably directly and not through the intermediate CO
formation. The main scientific issue is related to the fact that the systems investigated are mainly
modifications of conventional FT catalysts, rather than novel systems as probably required. The
role of CO2 in FT reactions remains contradictory. Hybrid FT–zeolite catalysts appear to be an
interesting possibility, but they are still not being developed on a scientific basis. Yields of over
55% in C2–C4 olefins are possible, but they need to be further increased (more than 75–80%) [32]
to exploit the process.
Significant advances in the co-polymerization of CO2 with epoxides to form cyclic and/or
polycarbonates or polyoils have been made. Various companies are exploring this route, which
appears to be close to commercialization. This route is interesting in terms of new materials
characteristics rather than in terms of its effective contribution to reducing GHG emissions.
Urea production is well established on a large scale, but there are further opportunities to
improve it. Commercial applications of CO2 conversion call for eco-sustainable synthesis of some
useful substituted ureas, carbamate and isocyanate in order to substitute toxic reagents. It is
evident that the key to CO2 conversion is the activation of either CO2 or co-reactants, under
as mild conditions as possible. Reactions with poor catalytic performance and/or those that take
place under severe conditions, such as isocyanate production from CO2 , need to be improved.
Electrocatalysis is offering new possibilities, either to produce small organic molecules to be
used in conjunction with or integrated into solar devices or as a valuable synthetic procedure.
There is the need to go beyond the conventional metal-type electrodes operating in the liquid
phase. Gas-phase operations or liquid phase in the presence of molecular catalysts (such as
pyridinium ions) are two promising directions to form either methanol or even long-chain
alcohols, but scientific effort in these areas is still too limited. The use of non-conventional
electrolytes, such as ionic liquids, is another attractive direction. Electrocatalytic carbonylation
is also an interesting possibility, but further effort is necessary.
Many interesting bio-catalytic routes using CO2 are also under development at an industrial
scale, such as acetone production (Evonik), bio-succinic acid from glucose and CO2 (many
companies), longer chain alcohols (Mitsubischi Chem.) and modification of syngas fermentation
processes to start from CO2 . Interesting developments are also in the area of hybrid enzyme–
photocatalysts.
The concept of artificial photosynthesis or leaves must be cited among the long-term
perspectives of CO2 utilization. Although often used to discuss only the formation of H2 by water
splitting or analogous approaches, there is an emerging interest in the possibility of realizing
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
of activation of CO2 for the design of new materials for energy and resource efficiency’ and the EU project
ECO2 CO2 ‘Eco-friendly biorefinery fine chemicals from CO2 photocatalytic reduction’ (contract no. 309701).
References
1. Appel AM et al. 2013 Frontiers, opportunities, and challenges in biochemical and chemical
catalysis of CO2 fixation. Chem. Rev. 113, 6621–6658. (doi:10.1021/cr300463y)
2. Costentin C, Robert M, Saveant J-M. 2013 Catalysis of the electrochemical reduction of carbon
dioxide. Chem. Soc. Rev. 42, 2423–2436. (doi:10.1039/c2cs35360a)
.........................................................
Acknowledgements. This work was carried out within the framework of the PRIN10–11 project ‘Mechanisms
29
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
more advanced devices, which instead use photochemical water oxidation (generating protons
and electrons, together with O2 ) to drive the electrocatalytic reduction of CO2 to chemicals or
fuels [36–38]. To focus discussion we have not discussed these aspects here, as they are already
covered to a good extent in the cited reviews.
Often the approach above is confused with the photochemical reduction of CO2 , which was
also not discussed here, but for different motivations. There is an increasing research interest in
this topic [119–122]. However, the actual productivities are very low, often at the same level as the
contaminations. The prospect of reaching the productivity necessary for a possible exploitation
of this technology is quite low. To reach a higher level of productivity, it is not only a matter of
developing better photocatalysts but also of using a different approach. It is necessary first to
physically separate the reaction zone of CO2 reduction from that of O2 evolution (from water
photo-conversion), otherwise CO2 and the products of CO2 reduction will compete and quench
the latter reaction. In addition, it is necessary to operate under conditions where the recovery of
the products is easy, at least requiring less energy than that incorporated in the products of CO2
reduction. For these reasons, we have omitted to discuss the photocatalytic reduction of CO2 ,
because we do not believe that it is a relevant path to move to a resource- and energy-efficient
chemical and fuel production.
This review has given a glimpse into the various novel possibilities that we believe will have
a role in the future scenario for chemical and energy sustainable production. The aim was not a
systematic survey, but rather to evidence how the use of CO2 will be a critical enabling element
for the sustainable future of chemical production. For this reason, a large part of the discussion
was dedicated to analysing the technological roadmap for CO2 chemical utilization and related
aspects: (i) how to assess the different routes for CO2 utilization, (ii) the critical question of the
perception of the role of CO2 utilization paths in the future of society, and (iii) a brief analysis of
emerging patent areas in relation to the technology roadmap.
The introduction of RE in the chemical production chain through CO2 utilization is a key
element to move the chemical industry towards low-carbon production. For this reason, a relevant
part of this review was dedicated to analysing this question and related aspects: (i) production
of RM and (ii) its impact on the ecosystem and climate change control. We have discussed how
the impact on GHG emissions will be large, and potentially not less than that expected from CCS
technologies or the use of biofuels, but with significantly lower costs [27].
The discussion has also provided evidence of on how CO2 utilization contributes to solving
some of the grand challenges facing our society: (i) mitigating climate change, (ii) preserving the
environment, (iii) using RE, and (iv) replacing fossil fuels. In tight integration with the use of
biomass, the use of CO2 provides a new sustainable scenario for chemical production [31–33]
and moves biorefineries to biofactories [34,35]. In a longer term visionary idea, it is possible to
create a CO2 economy where it will be possible to achieve full circle recycling of CO2 using RE
sources, similar to how plants photosynthetically convert CO2 to carbohydrates and O2 , but with
an intensified process and the capacity to control the type of products formed [36–39].
There are thus many stimulating possibilities offered by using CO2 and this review shows
this new vision on CO2 at the industrial, societal and scientific levels, but with some examples
evidencing how CO2 conversion will be at the core of the future of the chemical industry.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
30
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
3. Jiang Z, Xiao T, Kuznetsov VL, Edwards PP. 2010 Turning carbon dioxide into fuel. Phil.
Trans. R. Soc. A 368, 3343–3364. (doi:10.1098/rsta.2010.0119)
4. Dorner RW, Hardy DR, Williams FW, Willauer HD. 2010 Heterogeneous catalytic CO2
conversion to value-added hydrocarbons. Energy Environ. Sci. 3, 884–890. (doi:10.1039/
c001514h)
5. Ma J, Sun N, Zhang X, Zhao N, Xiao F, Wei W, Sun Y. 2009 A short review of catalysis for
CO2 conversion. Catal. Today 148, 221–231. (doi:10.1016/j.cattod.2009.08.015)
6. Centi G, Perathoner S. 2009 Opportunities and prospects in the chemical recycling of carbon
dioxide to fuels. Catal. Today 148, 191–205. (doi:10.1016/j.cattod.2009.07.075)
7. Centi G, Quadrelli EA, Perathoner S. 2013 Catalysis for CO2 conversion: a key technology
for rapid introduction of renewable energy in the value chain of chemical industries. Energy
Environ. Sci. 6, 1711–1731. (doi:10.1039/c3ee00056g)
8. Quadrelli EA, Centi G, Duplan J-L, Perathoner S. 2011 CO2 recycling: emerging largescale technologies with industrial potential. ChemSusChem, 4, 1194–1205. (doi:10.1002/
cssc.201100473)
9. Aresta M, Dibenedetto A. 2007 Utilisation of CO2 as a chemical feedstock: opportunities and
challenges. Dalton Trans. 28, 2975–2992. (doi:10.1039/b700658f)
10. Mikkelsen M, Jorgensen M, Krebs FC. 2010 The teraton challenge. A review of fixation and
transformation of carbon dioxide. Energy Environ. Sci. 32, 43–81. (doi:10.1039/b912904a)
11. Sakakura T, Choi J-C, Yasuda H. 2007 Transformation of carbon dioxide. Chem. Rev. 107,
2365–2387. (doi:10.1021/cr068357u)
12. Wang W, Wang S, Ma X, Gong J. 2011 Recent advances in catalytic hydrogenation of carbon
dioxide. Chem. Soc. Rev. 40, 3703–3727. (doi:10.1039/c1cs15008a)
13. Peters M, Kohler B, Kuckshinrichs W, Leitner W, Markewitz P, Muller TE. 2011 Chemical
technologies for exploiting and recycling carbon dioxide into the value chain. ChemSusChem
4, 1216–1240. (doi:10.1002/cssc.201000447)
14. Whipple DT, Kenis PJA. 2010 Prospects of CO2 utilization via direct heterogeneous
electrochemical reduction. J. Phys. Chem. Lett. 1, 3451–3458. (doi:10.1021/jz1012627)
15. Windle CD, Perutz RN. 2012 Advances in molecular photocatalytic and electrocatalytic CO2
reduction. Coord. Chem. Rev. 256, 2562–2570. (doi:10.1016/j.ccr.2012.03.010)
16. Yang Z-Z, He L-N, Gao J, Liu A-H, Yu B. 2012 CO2 utilization with C–N bond formation:
carbon dioxide capture and subsequent conversion. Energy Environ. Sci. 5, 6602–6639.
(doi:10.1039/c2ee02774g)
17. Aresta M. 2010 CO2 as chemical feedstock. Weinheim, Germany: Wiley-VCH.
18. Centi G, Perathoner S. 2014 Green CO2 : advances in CO2 utilization. New York, NY: Wiley and
Sons.
19. De Falco M, Iaquaniello G, Centi G. 2013 CO2 : a valuable source of carbon. Berlin, Germany:
Springer.
20. Olah GA, Goeppert A, Surya Prakash GK. 2009 Beyond oil and gas: the methanol economy, 2nd
edn. Weinheim, Germany: Wiley-VCH.
21. BayNews (The Bayer Press Server). 2011 See http://www.press.bayer.com/baynews/
baynews.nsf/id/F7D95A62E946F894C125783A002F2CB5.
22. Agarwal AS, Zhai Y, Hill D, Sridhar N. 2011 The electrochemical reduction of carbon dioxide
to formate/formic acid: engineering and economic feasibility. ChemSusChem 4, 1301–1310.
(doi:10.1002/cssc.201100220)
23. Lejkowski ML et al. 2012 The first catalytic synthesis of an acrylate from CO2 and an alkene:
a rational approach. Chem. Eur. J. 18, 14 017–14 025. (doi:10.1002/chem.201201757)
24. Plessow PN, Weigel L, Lindner R, Schaefer A, Rominger F, Limbach M, Hofmann P. 2013
Mechanistic details of the nickel-mediated formation of acrylates from CO2 , ethylene and
methyl iodide. Organometallics 32, 3327–3338. (doi:10.1021/om400262b)
25. Carbon Recycling International. 2012 See http://www.carbonrecycling.is.
26. Intergovernmental Panel on Climate Change (IPCC). 2005 Carbon dioxide capture and storage,
Sect. 7.3.4, p. 334. New York, NY: Cambridge University Press.
27. Barbato L, Centi G, Iaquaniello G, Mangiapane A, Perathoner S. 2014 Trading renewable
energy by using CO2 : an effective option to mitigate climate change and increase the use of
renewable energy sources. Energy Technol. 2, 453–461. (doi:10.1002/ente.201300182)
28. Centi G, Perathoner S. 2011 Facing the energy challenge through chemistry in a changing
world. In The chemical element: chemistry’s contribution to our global future (eds J GarciaMartinez, E Serrano-Torregrosa), ch. 8, pp. 269–307. Weinheim, Germany: Wiley-VCH.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
31
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
29. Centi G, Perathoner S. 2014 Perspectives and state of the art in producing solar fuels
and chemicals from CO2 . In Green CO2 : advances in CO2 utilization, pp. 1–24. New York,
NY: Wiley.
30. Centi G, Perathoner S. 2011 CO2 based energy vectors for the storage of solar energy.
Greenhouse Gases Sci. Technol. 1, 21–35. (doi:10.1002/ghg3.3)
31. Perathoner S, Centi G. 2014 CO2 recycling: a key strategy to introduce green energy in the
chemical production chain. ChemSusChem 7, 1274–1282. (doi:10.1002/cssc.201300926)
32. Lanzafame P, Centi G, Perathoner S. 2014 Catalysis for biomass and CO2 use through solar
energy: opening new scenarios for a sustainable and low-carbon chemical production. Chem.
Soc. Rev. 43, 7562–7580. (doi:10.1039/C3CS60396B)
33. Perathoner S, Centi G. 2014 A new scenario for green & sustainable chemical production.
J. Chin. Chem. Soc. 61, 719–730. (doi:10.1002/jccs.201400080)
34. Lanzafame P, Centi G, Perathoner S. 2014 Evolving scenarios for biorefineries and the impact
on catalysis. Catal. Today 234, 2–12. (doi:10.1016/j.cattod.2014.03.022)
35. Centi G, Perathoner S. 2013 Catalytic transformation of CO2 to fuels and chemicals, with
reference to biorefineries. In The role of catalysis for the sustainable production of bio-fuels and
bio-chemicals, (eds K Triantafyllidis, A Lappas, M Stöcker), ch. 16, pp. 529–555. Amsterdam,
The Netherlands: Elsevier.
36. Centi G, Perathoner S. 2012 Photoelectrochemical CO2 activation toward artificial leaves. In
Chemical energy storage (ed. R Schlögl), pp. 379–400. Berlin, Germany: De Gruyter.
37. Centi G, Perathoner S. 2013 Artificial leaves. In Kirk-Othmer encyclopedia. Hoboken, NJ: Wiley
and Son.
38. Bensaid S, Centi G, Garrone E, Perathoner S, Saracco G. 2012 Towards artificial leaves
for solar hydrogen and fuels from carbon dioxide. ChemSusChem 5, 500–521. (doi:10.1002/
cssc.201100661)
39. Centi G, Perathoner S. 2010 Towards solar fuels from water and CO2 . ChemSusChem 3,
195–208. (doi:10.1002/cssc.200900289)
40. KPMG International. 2010 The future of the European chemical industry. Publication no.
1001503. See http://www.kpmg.com/Global/en/IssuesAndInsights/ArticlesPublications/
Lists/Expired/The-Future-of-the-European-Chemical-Industry.pdf.
41. ATKearner. 2012 Chemical industry vision 2030: a European perspective. See https://www.
atkearney.com/documents/10192/536196/Chemical+Industry+Vision+2030+A+European+
Perspective.pdf/7178b150–22d9–4b50–9125–1f1b3a9361ef.
42. Deloitte Touche Tohmatsu Chemical Group and Deloitte Research (US). 2010 The decade
ahead. Preparing for an unpredictable future in the global chemical industry. See http://
www2.deloitte.com/content/dam/Deloitte/global/Documents/Manufacturing/gx_the
decadeahead_final_lowres_v3.pdf.
43. Valencia RC. 2013 The future of the chemical industry by 2050. Weinheim, Germany: Wiley-VCH.
44. Cavani F, Centi G, Perathoner S, Trifirò F. 2009 Sustainable industrial chemistry: principles, tools
and industrial examples. Germany: Wiley-VCH.
45. Allianz Global Investors. 2013 The ‘green’ Kondratieff. See https://www.allianzgloba
linvestors.de/cms-out/kapitalmarktanalyse/docs/pdf-eng/analysis-and-trends-the-greenkondratieff.pdf.
46. Capoferri D, Cucchiella B, Iaquaniello G, Mangiapane A, Abate S, Centi G. 2011 Catalytic
partial oxidation and membrane separation to optimize the conversion of natural gas to
syngas and hydrogen. ChemSusChem 4, 1787–1795. (doi:10.1002/cssc.201100260)
47. Sai Prasad PS, Wook Bae J, Jun K-W, Lee K-W. 2008 Fischer–Tropsch synthesis by carbon
dioxide hydrogenation on Fe-based catalysts. Catal. Surv. Asia 12, 170–183. (doi:10.1007/
s10563-008-9049-1)
48. Fukuoka S, Fukawa I, Tojo M, Oonishi K, Hachiya H, Aminaka M, Hasegawa K, Komiya
K. 2010 A novel non-phosgene process for polycarbonate production from CO2 : green and
sustainable chemistry in practice. Catal. Surv. Asia 14, 146–163. (doi:10.1007/s10563-0109093-5)
49. Jessop PG, Ikariya T, Noyori R. 1995 Homogeneous hydrogenation of carbon dioxide. Chem.
Rev. 95, 259–272. (doi:10.1021/cr00034a001)
50. Riduan SN, Zhang Y, Ying JY. 2009 Conversion of CO2 into methanol with silanes
over N-heterocyclic carbene catalysts. Angew. Chem. Int. Ed. 48, 3322–3325. (doi:10.1002/
anie.200806058)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
32
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
51. Matsuo T, Kawaguchi H. 2006 From carbon dioxide to methane: homogeneous reduction
of CO2 with hydrosilanes catalyzed by zirconium-borane complexes. J. Am. Chem. Soc. 128,
12 362–12 363. (doi:10.1021/ja0647250)
52. Huang F, Zhang C, Jiang J, Wang Z-X, Guan H. 2011 How does the nickel pincer complex
catalyze the conversion of CO2 to a methanol derivative? A computational mechanistic
study. Inorg. Chem. 50, 3816–3825. (doi:10.1021/ic200221a)
53. Sgro MJ, Stephan DW. 2012 Frustrated Lewis pair inspired carbon dioxide reduction
by a ruthenium tris(aminophosphine) complex. Angew. Chem. Int. Ed. 51, 11 343–11 345.
(doi:10.1002/anie.201205741)
54. Wesselbaum S, vom Stein T, Klankermayer J, Leitner W. 2012 Hydrogenation of CO2 to
methanol using a homogeneous ruthenium-phosphine catalyst. Angew. Chem. Int. Ed. 51,
7499–7502. (doi:10.1002/anie.201202320)
55. Ashley AE, Thompson AL, O’Hare D. 2009 Non-metal-mediated homogeneous
hydrogenation of CO2 to CH3 OH. Angew. Chem. Int. Ed. 48, 9839–9843. (doi:10.1002/anie.
200905466)
56. Balaraman E, Gunanathan C, Zhang J, Shimon LJW, Milstein D. 2011 Efficient hydrogenation
of organic carbonates, carbamates and formates indicates alternative routes to methanol
based on CO2 and CO. Nat. Chem. 3, 609–614. (doi:10.1038/nchem.1089)
57. Zhang Y, Riduan SN. 2011 Catalytic hydrocarboxylation of alkenes and alkynes with CO2 .
Angew. Chem. Int. Ed. 50, 6210–6212. (doi:10.1002/anie.201101341)
58. Ampelli C, Centi G, Passalacqua R, Perathoner S. Submitted. Electrolyte-less design of PEC
cells for solar fuels: prospects and open issues in the development of cells and related
catalytic electrodes.
59. Benson EE, Kubiak CP, Sathruma AJ, Smieja JM. 2009 Electrocatalytic and homogeneous
approaches to conversion of CO2 to liquid fuels. Chem. Soc. Rev. 38, 89–99. (doi:10.1039/
b804323j)
60. Keith JA, Carter EA. 2013 Electrochemical reactivities of pyridinium in solution:
consequences for CO2 reduction mechanisms. Chem. Sci. 4, 1490–1496. (doi:10.1039/
c3sc22296a)
61. Barton CE, Lakkaraju PS, Rampulla DM, Morris AJ, Abelev E, Bocarsly AB. 2010 Using a oneelectron shuttle for the multielectron reduction of CO2 to methanol: kinetic, mechanistic, and
structural insights. J. Am. Chem. Soc. 132, 11 539–11 551. (doi:10.1021/ja1023496)
62. Morris AJ, McGibbon RT, Bocarsly AB. 2011 Electrocatalytic carbon dioxide activation: the
rate-determining step of pyridinium-catalyzed CO2 reduction. ChemSusChem 4, 191–196.
(doi:10.1002/cssc.201000379)
63. Martindale BCM, Compton RG. 2012 Formic acid electro-synthesis from carbon dioxide in a
room temperature ionic liquid. Chem. Commun. 48, 6487–6489. (doi:10.1039/c2cc32011h)
64. Jhong H-R, Ma S, Kenis PJA. 2013 Electrochemical conversion of CO2 to useful chemicals:
current status, remaining challenges, and future opportunities. Curr. Opin. Chem. Eng. 2, 191–
199. (doi:10.1016/j.coche.2013.03.005)
65. Lu Q, Rosen J, Zhou Y, Hutchings GS, Kimmel YC, Chen JG, Jiao F. 2014 A selective and
efficient electrocatalyst for carbon dioxide reduction. Nat. Commun. 5, 3242. (doi:10.1038/
ncomms4242)
66. Jia G, Gao Y, Zhang W, Wang H, Cao Z, Li C, Liu J. 2013 Metal-organic frameworks as
heterogeneous catalysts for electrocatalytic oxidative carbonylation of methanol to dimethyl
carbonate. Electrochem. Commun. 34, 211–214. (doi:10.1016/j.elecom.2013.06.013)
67. Gallou I. 2007 Unsymmetrical ureas. Synthetic methodologies and application in drug
design. Org. Prep. Proc. Int. 39, 355–383. (doi:10.1080/00304940709458592)
68. Nitz J-J. 2013 CO2-Basierte Acetonfermentation (COOBAF). In Proc. BMBFFördermaßnahme
‘Technologien für Nachhaltigkeit und Klimaschutz-Chemische Prozesse und stoffliche Nutzung von
CO2 ’, Berlin, Germany, 9–10 April 2013.
69. Beaupreza JJ, De Mey M, Soetaert WK. 2010 Microbial succinic acid production: natural
versus metabolic engineered producers. Process Biochem. 45, 1103–1114. (doi:10.1016/
j.procbio.2010.03.035)
70. Cheng K-K, Zhao X-B, Zeng J, Zhang J-A. 2012 Biotechnological production of succinic acid:
current state and perspectives. Biofuel Bioprod. Bioref. 6, 302–318. (doi:10.1002/bbb.1327)
71. Zhang K, Sawaya MR, Eisenberg DS, Liao JC. 2008 Expanding metabolism for biosynthesis
of non-natural alcohols. Proc. Natl Acad. Sci. USA 105, 20 653–20 658. (doi:10.1073/
pnas.0807157106)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
33
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
72. Atsumi S, Higashide W, Liao JC. 2009 Direct photosynthetic recycling of carbon dioxide to
isobutyraldehyde. Nat. Biotechnol. 27, 1177–1180. (doi:10.1038/nbt.1586)
73. Woolerton TW, Sheard S, Reisner E, Pierce E, Ragsdale SW, Armstrong FA. 2010 Efficient and
clean photoreduction of CO2 to CO by enzyme-modified TiO2 nanoparticles using visible
light. J. Am. Chem. Soc. 132, 2132–2133. (doi:10.1021/ja910091z)
74. Woolerton TW, Sheard S, Pierce E, Ragsdale SW, Armstrong FA. 2011 CO2 photoreduction
at enzyme-modified metal oxide nanoparticles. Energy Environ. Sci. 4, 2393–2399.
(doi:10.1039/c0ee00780c)
75. Chaudhary YS, Woolerton TW, Allen CS, Warner JH, Pierce EH, Ragsdale SW, Armstrong
FA. 2012 Visible light-driven CO2 reduction by enzyme coupled CdS nanocrystals. Chem.
Commun. 48, 58–60. (doi:10.1039/c1cc16107e)
76. Lazarus O et al. 2009 Visible light-driven H2 production by hydrogenases attached to dyesensitized TiO2 nanoparticles. J. Am. Chem. Soc. 131, 14 157–14 166. (doi:10.1021/ja905797w)
77. Henstra AH, Sipma J, Rinzema A, Stams AJM. 2007 Microbiology of synthesis gas
fermentation for biofuel production. Curr. Opin. Biotechnol. 18, 200–206. (doi:10.1016/
j.copbio.2007.03.008)
78. Daniell J, Köpke M, Simpson SD. 2012 Commercial biomass syngas fermentation. Energies 5,
5372–5417. (doi:10.3390/en5125372)
79. Dechema. 2009 Position paper on the utilisation and storage of CO2 . Frankfurt am Main,
Germany: Verband der Chemischen Industrie e.V.
80. Dechema/IEA/ICCA. 2013 Technology roadmap ‘energy and GHG reductions in the chemical
industry via catalytic processes’. Frankfurt am Main, Germany: Dechema.
81. Frost & Sullivan Corp. 2013 Market assessment of energy conservation and recovery technologies
for CO2 reduction in Europe and North America. San Antonio, TX: Frost & Sullivan.
82. Parsons Brinckerhoff/Global CCS Institute. 2011 Accelerating the uptake of CCS: industrial use
of captured carbon dioxide. Melbourne, Australia: Global CCS Institute.
83. Styring P. 2013 Carbon dioxide utilization off-setting the costs of CCS and providing a route
to renewable energy storage. Presented at ‘CO2 reuse workshop’ organized by DG Clima
and DG JRC, 7 June 2013, Brussels, Belgium.
84. Thybaud N, Lebain D. 2010 Panorama des voies de valorisation du CO2. Angers, France: French
Agence de l’Environnement et de la Maîtrise de l’Energie.
85. SPIRE (Sustainable Process Industry through Resource and Energy Efficiency). 2013
SPIRE roadmap. See http://www.spire2030.eu/uploads/Modules/Documents/spire-road
map_broch_july2013_pbp.pdf.
86. CEFIC (European Chemical Industry Council). 2013 European chemistry for growth.
Unlocking a competitive, low carbon and energy efficient future. See http://www.cefic.
org/Documents/PolicyCentre/Energy-Roadmap-The%20Report-European-chemistry-forgrowth.pdf.
87. Centi G, van Santen RA. 2009 Catalysis for renewables: from feedstock to energy production.
Weinheim, Germany: Wiley-VCH.
88. Centi G, Lanzafame P, Perathoner S. 2012 Introduction and general overview. In Catalysis
for alternative energy generation (eds L Guczi, A Erdôhelyi), ch 1, pp. 1–28. Berlin, Germany:
Springer.
89. Landeweerd L, Surette M, van Driel C. 2011 From petrochemistry to biotech: a European
perspective on the bio-based economy. Interface Focus 1, 189–195. (doi:10.1098/rsfs.2010.0014)
90. European Commission. 2011 Bio-based economy in Europe: state of play and future potential.
See http://ec.europa.eu/research/consultations/bioeconomy/bio-based-economy-for-eur
ope-part1.pdf.
91. Committee on Climate Change. 2011 Is bioenergy low-carbon? See http://downloads.
theccc.org.uk.s3.amazonaws.com/Bioenergy/1463%20CCC_Bio-TP1_locarb_FINALwith%
20BkMks.pdf.
92. Institute for European Environmental Policy. 2012 The GHG emissions intensity of
bioenergy. Does bioenergy have a role to play in reducing Europe’s GHG emissions? See
http://www.ieep.eu/assets/1008/IEEP_-_The_GHG_Emissions_Intensity_of_Bioenergy_-_
October_2012.pdf.
93. Centi G, Perathoner S, Passalacqua R, Ampelli C. 2011 Solar production of fuels from water
and CO2 . In Carbon-neutral fuels and energy carriers (eds NZ Muradov, TN Veziroǧlu), ch. 4,
pp. 291–323. Boca Raton, FL: CRC Press.
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
34
.........................................................
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
94. Ni M, Leung MKH. 2008 Technological development of hydrogen production by
solid oxide electrolyzer cell (SOEC). Int. J. Hydrog. Energy 33, 2337–2354. (doi:10.1016/
j.ijhydene.2008.02.048)
95. Laguna-Bercero MA. 2012 Recent advances in high temperature electrolysis using solid oxide
fuel cells: a review. J. Power Sources 203, 4–16. (doi:10.1016/j.jpowsour.2011.12.019)
96. Wang M, Wang Z, Gong X, Guo Z. 2014 The intensification technologies to water
electrolysis for hydrogen production: a review. Renew. Sustain. Energy Rev. 29, 573–588.
(doi:10.1016/j.rser.2013.08.090)
97. Graves C, Ebbesen SD, Mogensen M. 2011 Co-electrolysis of CO2 and H2 O in solid oxide
cells: performance and durability. Solid State Ion. 192, 398–403. (doi:10.1016/j.ssi.2010.06.014)
98. Redissi Y, Bouallou C. 2013 Valorization of carbon dioxide by Co-electrolysis of
CO2 /H2 O at high temperature for syngas production. Energy Proc. 37, 6667–6678.
(doi:10.1016/j.egypro.2013.06.599)
99. Genovese C, Ampelli C, Perathoner S, Centi G. 2013 Electrocatalytic conversion of
CO2 to liquid fuels using nanocarbon-based electrodes. J. Energy Chem. 22, 202–213.
(doi:10.1016/S2095-4956(13)60026-1)
100. Ampelli C, Passalacqua R, Genovese C, Perathoner S, Centi G. 2011 A novel photoelectrochemical approach for the chemical recycling of carbon dioxide to fuels. Chem. Eng.
Trans. 25, 683–688.
101. Ampelli C, Passalacqua R, Perathoner S, Centi G. 2009 Nano-engineered materials for H2
production by water photo-electrolysis. Chem. Eng. Trans. 17, 1011–1016.
102. Pearson RJ, Eisaman MD, Turner JWG, Edwards PP, Jiang Z, Kuznetsov VL, Littau KA, di
Marco L, Taylor SRG. 2012 Energy storage via carbon-neutral fuels made from CO2 , water
and renewable energy. Proc. IEEE 100, 440–460. (doi:10.1109/JPROC.2011.2168369)
103. STOA (European Parliament). 2014 Methanol: a future transport fuel based on hydrogen and CO2 ?
IP/A/STOA/FWC/2008–096/Lot1/C1/SC3. Brussels, Belgium: STOA.
104. Deng S, Hynes R. 2012 Advanced combined cycle systems based on methanol indirect
combustion. J. Eng. Gas Turbines Power 134, 063001. (doi:10.1115/1.4005818)
105. Santin M, Traverso A, Magistri L, Massardo A. 2010 Thermo-economic analysis of SOFCGT hybrid systems fed as auxiliary power systems on-board ships. Energy 35, 1077–1083.
(doi:10.1016/j.energy.2009.06.012)
106. Renewable Energy Policy Network for the 21st Century (REN21). 2013 Renewables
2013 global status report. See www.ren21.net/Portals/0/documents/Resources/GSR/2013/
GSR2013_highres.pdf.
107. Zickfeld F, Wieland A. 2012 Desert power 2050. See www.diieumena.com/fileadmin/
flippingbooks/dp2050_exec_sum_engl_web.pdf.
108. International Energy Agency. 2010 Energy technology perspectives—scenarios & strategies to
2050. Paris, France: OECD/IEA.
109. Johnson D. 2012 Global methanol market review. Presented at Pemex Petrochemistry,
June 2012, Mexico City. See http://www.ptq.pemex.com/productosyservicios/
eventosdescargas/Documents/Foro%20PEMEX%20Petroqu%C3%ADmica/2012/PEMEX_
DJohnson.pdf.
110. NETL (National Energy Technology Laboratory). 2010Worldwide gasification database. See
http://www.netl.doe.gov/technologies/coalpower/gasification/worlddatabase/current
world.html.
111. Rohde MP, Unruh D, Schaub G. 2006 Membrane application in Fischer–Tropsch synthesis
reactors—overview of concepts. Catal. Today 106, 143–148. (doi:10.1016/j.cattod.2005.07.124)
112. Polychronopoulou K, Kalamaras CM, Efstathiou AM. 2011 Ceria-based materials for
hydrogen production via hydrocarbon steam reforming and water–gas shift reactions. Recent
Patents Mater. Sci. 4, 122–145.
113. Brisse A, Schefold J. 2012 High temperature electrolysis at EIFER, main achievements at cell
and stack level. Energy Proc. 29, 53–63. (doi:10.1016/j.egypro.2012.09.008)
114. Fu Q, Mabilat C, Zahid M, Brisse A, Gautier L. 2010 Syngas production via high-temperature
steam/CO2 co-electrolysis: an economic assessment. Energy Environ. Sci. 3, 1382–1397.
(doi:10.1039/c0ee00092b)
115. Graves C, Ebbesen SD, Mogensen M, Lackner KS. 2011 Sustainable hydrocarbon fuels by
recycling CO2 and H2 O with renewable or nuclear energy. Renew. Sustain. Energy Rev. 15,
1–23. (doi:10.1016/j.rser.2010.07.014)
Downloaded from http://rsta.royalsocietypublishing.org/ on July 31, 2017
CH3 OH
CODH
CCS
CO2
CRI
DME
DNV
EOR
EU
FT
GE
GHG
Gton
GWh
IPCC
LCA
MTBE
Mton
MWth
NG
P2G
PV
RE
R&D
RM
RWGS
SOEC
SPIRE
UCLA
USPTO
WGS
methanol
carbon monoxide dehydrogenase
carbon capture and storage
carbon dioxide
Carbon Recycling International
dimethyl ether
Det Norske Veritas Inc.
enhanced oil recovery
European Union
Fischer–Tropsch
General Electric
greenhouse gas
giga tons
giga watts per hour
Intergovernmental Panel on Climate Change
life cycle analysis
methyl tert-butyl ether
million tons
megawatt thermal
natural gas
power to gas
photovoltaic
renewable energy
research and development
renewable methanol
reverse water gas shift
solid oxide electrolyser cell
Sustainable Process Industry through Resource and Energy Efficiency,
a European Public–Private Partnership
University of California, Los Angeles
United States Patent and Trademark Office
water gas shift
.........................................................
Glossary
35
rsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373: 20140177
116. Grabow LC, Mavrikakis M. 2011 Mechanism of methanol synthesis on Cu through CO2 and
CO hydrogenation. ACS Catal. 1, 365–384. (doi:10.1021/cs200055d)
117. Izumi Y. 1997 Selective ethanol synthesis from carbon dioxide: roles of rhodium catalytic
sites. Platinum Metals Rev. 41, 166–170.
118. Ogura K. 2013 Electrochemical reduction of carbon dioxide to ethylene: mechanistic
approach. J. CO2 Utilization 1, 43–49. (doi:10.1016/j.jcou.2013.03.003)
119. Kumar B, Llorente M, Froehlich J, Dang T, Sathrum A, Kubiak CP. 2012 Photochemical
and photoelectrochemical reduction of CO2 . Annu. Rev. Phys. Chem. 63, 541–569.
(doi:10.1146/annurev-physchem-032511-143759)
120. Reithmeier R, Bruckmeier C, Rieger B. 2012 Conversion of CO2 via visible light promoted
homogeneous redox catalysis. Catalysts 2, 544–571. (doi:10.3390/catal2040544)
121. Habisreutinge SN, Schmidt-Mende L, Stolarczyk JK. 2013 Photocatalytic reduction of
CO2 on TiO2 and other semiconductors. Angew. Chem. Int. Ed. Engl. 52, 7372–408.
(doi:10.1002/anie.201207199)
122. Neaţu Ş, Maciá-Agulló JA, Garcia H. 2014 Solar light photocatalytic CO2 reduction: general
considerations and selected bench-mark photocatalysts. Int. J. Mol. Sci. 15, 5246–5262.
(doi:10.3390/ijms15045246)