Nano Catalysis
• Reduce exhaust emissions with catalytic converters
• Reduce precious metal use through nanoparticles
UNF ST: Nanofabrication EML 6933 Brian White
Pd: A Catalyst
HC (hyrdocarbons) & CO require oxygenation —> CO2 & H2O
NOx requires reduction —> N2 & O2
NOx is an issue at high temperatures and thus not at start-up
UNF ST: Nanofabrication EML 6933 Brian White
Overview
• Short videos on toxic pollutants in the air
• What is a cat?..It's a catalytic converter
• History
• Pollution- types, chemical rxn's, agencies,
methods used to ↓ emissions
• Structure
• Nano techniques for manufacture..Top down vs Bottom up
• Future work
UNF ST: Nanofabrication EML 6933 Brian White
What is a cat?
• Catalytic converters use catalysts, which speed up
chemical rxn's, and consist of the precious metals: Pt,
Pd & Rh over a ceramic base.
• Pt & Pd oxidize CO & UHC (unburned
hydrocarbons)… CDR (carbon dioxide removal) is achieved with the CO2ube. CO is a greenhouse gas.
2
• Pt & Rh reduce NOx ..NOx forms when the combustion chamber is >2700°C
Results:
• CO & UHC are ↓ 97%
• 70% of CO & UHC occur during cold-start emissions,
therefore before the “light-off” period (when
temperatures
are <300°C)
UNF ST: Nanofabrication EML 6933 Brian White
History
• Lead (fuel additive TEL) poisoned cat!
• TEL was added in the 1920’s to raise octane levels
• TEL was significantly reduced by the EPA in 1976.
• Eugene Houdry
• 1950 - studies of smog in LA were published
• Founded the company Oxy-Catalyst to develop cats for
gasoline engines. Idea was ahead of its time
• 1973- LA air pollution episode
• 1974- The first cat in the US Developed by John J. Mooney and Carl D. Keith at
the Engelhard Corporation
• 1975- Every new car has to have a cat EPA mandate
UNF ST: Nanofabrication EML 6933 Brian White
Videos..FYE
•
Video 1
•
Video 2
•
Video 3
UNF ST: Nanofabrication EML 6933 Brian White
Pollution
• CAA (Clean Air Act) requires EPA to set NAAQS (National Ambient Air
Quality Standards)
• 6 harmful pollutants
• CO, Pb, NOx, SO2
• PM- particulate matter (PM2.5 is thought of and not PM10)
• O3- ground level ozone. This is a secondary pollutant resulting from
NOx, VOC (volatile organic carbons) & sunlight
• Ideal fuel only has HC's
• Actual fuel has N, S, P, Fe, Cu, Ni, Cr, Si.
• Can pre-treat via further processing but there is an added cost.
• Smog
• Smog- smoke & fog. CO, NOx, VOC (by means of negative crankcase ventilation & tailpipe),
SO2 & HC
UNF ST: Nanofabrication EML 6933 Brian White
Chemical Rxn's of
Isooctane/Gasoline/Petrol
Complete combustion:
C8H18 + z(O2 + 3.76N2) → a(CO2) + b(H2O) + 3.76z(N2)
C: a = 8, H: b = 9, O: z = a + (1/2)b = 12.5
3.76?
X/0.79 = 1/0.21 → X = 3.76
(air is 79% N, 21% O)
Incomplete combustion:
C8H18 + z(O2 + 3.76N2) → a(CO2) + b(CO) + c(H2O) + d(H2)
z = 12.5, C: 8 = a + b, H: 9 = c +d, O: 12.5 = a + (1/2)b + (1/2)c
4th eq: Water gas shift rxn:
O + N2 → NO + N
N + O2 → NO + O2
N + OH → NO + H
UNF ST: Nanofabrication EML 6933 Brian White
..CO & H2 = water gas
Chemical Rxn's in Catalysis
Oxidation:
C + H2O → CO + H2
2CO + O2 → 2CO2
C8H18 + 12.5O2 = 8CO2 + 9H2O
RH → R → RO2 → RCHO → RCO → CO where R is a HC radical
CO + OH ↔ CO2 + H
Reduction
2NOx → N2 + O2x
UNF ST: Nanofabrication EML 6933 Brian White
Agencies
•
Air Pollution Control Act, 1955
•
Clean Air Act, 1963..1990 Clean Air Act- 189 hazardous air pollutants
were defined.
•
Motor Vehicle Air Pollution Control Act, 1965
•
Air Quality Act, 1967
•
Clean Air Act Amendments, 1970, 1977, 1990
•
US Environmental Protection Agency (USEPA)..Green Chemistry Pgm
•
National Ambient Air Quality Standards (NAAQS)
•
FL State Implementation Plan (SIP)
•
National Emission Standards for Hazardous Air Pollutants (NESHAP)
•
New Source Performance Standards (NSPS)
UNF ST: Nanofabrication EML 6933 Brian White
↓ Air Pollution (i.e. GHG & toxicity)
• Improve engine combustion
• Reformulation of fuels (pre-treatment)
• Contains oxygenates (i.e. alcohol or ether..ethanol & MTBE).
• 2% O added to burn cleaner-> 11% MTBE. 87% of the additive is MTBE not ethanol.
• Ethanol- highly volatile (high vapor pressure) ∴ evaporates readily especially in summer creating smog, and
separates from gasoline.
• 30% of gasoline uses it. It is in 19 states & D.C..
• Oxidation/reduction catalysts
• Exhaust Gas recirculation (EGR)..most SI & diesel engines have it
• Avoid cold start- Thermal management systems (TMS)
• Phase change material (PCM)- Sodium acetate- latent heat storage, solid-liquid
• Variable-Conduction Insulation (VCI)- metal hydride -stores heat to minimize cold start emissions
UNF ST: Nanofabrication EML 6933 Brian White
GHG emission by Economic Sectors
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Cost Breakdown TWC
UNF ST: Nanofabrication EML 6933 Brian White
Shorten light-off time
Light-off temp- temp at which
50% of the emissions are being
converted as they pass through
the catalytic converter
EHC- electrical heating of
catalytic convertors (2kW- using
car battery, issue with battery
capacity since it requires power
for 25-30s)
APEHC- alternator powered
electrically heated catalyst.
5-mile trip, starting the car cold
generates about
30% more NOX and 60% more
CO than starting the car when it
is warm
UNF ST: Nanofabrication EML 6933 Brian White
Cat
Determines A/F ratio then data sent RT
to control electronic fuel injection and
thus emission control
UNF ST: Nanofabrication EML 6933 Brian White
TWC – oxidizing/reducing cat
1981- two way-> three way to reduce NOx
Reaction of Exhaust with Catalyst (TWC) Resulting in Clean Emissions
http://www.walkerexhaust.com/support/understanding-catalytic-converter/evolution-of-the-catalytic-converter
UNF ST: Nanofabrication EML 6933 Brian White
Platinum Group Metals - PGM
UNF ST: Nanofabrication EML 6933 Brian White
Cost $ - Precious Metals
3 – 7 g of Pt per cat
Relative amounts of each metal: Pt:Pd:Rh = 5:2.5:1
Cost of each metal/cat: $354-$152: $90-$39: $48-$21
70 – 90% less precious metals by using 5 nm diameter nanoparticles, which have a
higher surface area to volume ratio
UNF ST: Nanofabrication EML 6933 Brian White
Design/ Structure
1) Catalyst support/ substrateFirst.. Pellet-type Al2O3
Then.. ceramic monolith w/ “Honeycomb” structure
Thin walled- ceramic (i.e. cordierite) or metal block (i.e. Al2O3, Kanthal (FeCrAl))
Parallel channels- 0.5 – 10 mm dia. Straight paths. Why?
2) Wash coatCarrier for the catalytic materials, layer of inorganic metal oxides (i.e. Al2O3, SiO2, & TiO2)
Heterogeneous catalyst
Rough- to ↑ surface area
3) Noble metalsPt, Pd, Rh (Ca, Pb, As tailings)
Ce, Fe, Mg, Zr & Ni, Cu are also used but create toxic by-products
UNF ST: Nanofabrication EML 6933 Brian White
Design/ Structure
UNF ST: Nanofabrication EML 6933 Brian White
Potential Issues
Catalyst Bed Deactivation
Thermal deactivation- sintering, solid-state transform
Fouling- physical deposition of substances
Crushing- mechanical forces on catalyst (high velocity exhaust
gases)
Poisoning- occurs due to layer forming on the wash-coat
surface (i.e. Zn, Ca, & Mg phosphates and CePO4, Ce(PO3)3, & AlPO4
UNF ST: Nanofabrication EML 6933 Brian White
Nano Catalysis
• Pt nanoparticles (colloidal spheres) supported on functionalized TiO2
• Nanoporous silica layer, as cathode catalyst, improves the thermostability
of the Pt, preventing sintering/agglomeration of Pt.
UNF ST: Nanofabrication EML 6933 Brian White
Zeolite
• Microporous, aluminosilicate minerals used as
commercial adsorbents and catalysts
• Alumina & silica with sodium hydroxide
• Sodium aluminate & sodium silicate
• Abundance of cations such as Na+, K+, Ca2+, Mg2+, etc.
• Large surface area
• Molecular sieve- sorts molecules on a size
exclusion process
UNF ST: Nanofabrication EML 6933 Brian White
Metal-Organic Framework (MOF)
• MOF has exposed sites of metal cation (Mg2) that attach to CO2
• CO2 is adsorbed to a greater extent by appending diamines to the open
coordination sites
• Coordination network- A metal ion or cluster of metal ions and an
organic molecule (ligands- anions, linker, or complexing agent)
• 1 gram has a surface area of greater than 3 football fields!
• Well ordered, ultra-porous crystals
• Chemisorption- strong binding
• Physisorption- light relaxing of molecule on surface
UNF ST: Nanofabrication EML 6933 Brian White
MOF
UNF ST: Nanofabrication EML 6933 Brian White
SWNH’s (Single Walled Nanohorns)
SWNH’s
•Derived from SWNT’s
•C or TiO2
•Coated with (d < 5 nm) Pt nanoparticles
•40–50 nm in tubule length
•2–3 nm in diameter
•20° cone opening angle
• 1000's of SWNH’s form the ‘dahlia-like' and
‘bud-like’ structured aggregates with d = 80-100
nm.
UNF ST: Nanofabrication EML 6933 Brian White
Videos
• Cruciblehttp://www.tubechop.com/watch/5698522
• Zeolitehttp://www.tubechop.com/watch/5698549
UNF ST: Nanofabrication EML 6933 Brian White
Testing methods
UNF ST: Nanofabrication EML 6933 Brian White
Monodisperse Particles
• Ensure particles are the same
size using dynamic light
scattering
• Monochromatic light source (i.e.
laser) is sent through a polarizer
that hits the particles creating a
speckle pattern (interference of
diffracted light)
• Diffracted light is then sent
through another polarizer
• Repeated at short time intervals
UNF ST: Nanofabrication EML 6933 Brian White
Future Work
• The goal is to grow different shapes that make surfaces more
catalytically active
• At the moment only about 10 percent of the platinum particles in a catalytic converter are
active
• Save cost by using less expensive cobalt catalyst material
• Increase catalysis activity through tetrapod structure (crystal
structure of a tetrahedral shape)
• Nano and microscale patterning methods with varying degrees of accuracy exist (i.e.
heteroepitaxy)
UNF ST: Nanofabrication EML 6933 Brian White
References
1) Shah, R.. “Automotive Air Pollution and its Control by Catalytic Converters.” University of Illinois at Urbana-Champaign. (2013).
2) Lecture Series Heterogeneous Catalysis: Catalyst Deactivation.” (2011).
http://w999.rzberlin.mpg.de/acnew/department/pages/teaching/pages/teaching__wintersemester__2010_2011/manfred_baerns__catalyst_deactivation_
_110121.pdf
3) Heberling, M.. “Government-Reformulated Gas: Bad in More Ways than One. The Freeman.
Reformulated Gas Is Useless at Best, Expensive and Harmful at Worst.” (2003) http://fee.org/freeman/detail/government-reformulated-gas-bad-in-moreways-than-one
4) Stafford, N.. “Catalytic Converters go Nano.” Royal Society of Chemistry. Web. (2007).
http://www.rsc.org/chemistryworld/News/2007/October/10100701.asp
5) Thole, J.. “Nanotechnology promises better catalytic converter.” Web. http://phys.org/news204827696.html . (2010)
6) Tilley, R.. “Catalytic Converters and Platinum Nanoparticles.” The University of Waikato. http://www.sciencelearn.org.nz/Contexts/Nanoscience/SciMedia/Video/Catalytic-converters-and-platinum-nanoparticles (2008).
7) Serp, P., Philippot, K.. “Nanomaterials in Catalysis.”
8) Suib, S.. “New and Future Developments in Catalysis: Catalysis by Nanoparticles.”
9) Metal-Organic Frameworks: CO2 Capture”. Long Group. Web. http://alchemy.cchem.berkeley.edu/metal-organic-frameworks.html
UNF ST: Nanofabrication EML 6933 Brian White
Quiz ?’s
1) What precious metals are used for oxidation and which ones for
reduction?
2) US EPA mandates what and in which year?
3) What does lead do besides being a neurotoxin?
4) What does the acronym TWC stand for?
5) a) The parallel channels of the monolith ceramic should have what
type of channels and why? Hint: so engine performance stays high.
b) Pt is embedded in what type of nanofiber?
c) i) What does a catalyst do?
c) ii) Name at least one nano-catalytic method?
d) What is nanofabrication and how can it improve cat's?
UNF ST: Nanofabrication EML 6933 Brian White
Answers
1)
Pt, Pd – oxidize & Pt, Rh – reduce
2)
Every car has a cat as of 1975
3)
Poisons cat
4)
Three-way catalytic converter
5)
a) Straight paths to decrease pressure loss.
b) TiO2
c) i) Speeds up a rxn
c) ii) MOF’s, SWNH’s, zeolite, crucible
d) Manufacturing materials (or devices) in the size range of 0.1 - 100
nm. Use less material through increased surface area to volume ratio.
UNF ST: Nanofabrication EML 6933 Brian White