Selective Oxidation of C-H Bonds
Raw Materials Change in Chemical Industry and Efficient Energy Storage
Model studies of C-H Activation
Introduction
Objectives and strategy
Highlights
• Deeper understanding of the structural dynamics of the active sites and the entire catalyst material
• Theoretical and experimental investigation of the interactions of catalyst
and reaction dynamics
• Identification of key factors controlling the performance of catalysts
• Design of catalysts with adjustable “smart” surface properties
• Immediate transfer of promising catalysts and process concepts to application
• Oxidative coupling of CH4 on Li-doped and non-doped MgO
• The calculated energy barriers for CH4 activation by hydrogen abstraction at oxygen
radical sites of Li-doped MgO are unrealistically low.
• Lundsford mechanism needs to be revised
• Temperature programmed reaction experiments: the same active sites are
responsible for activation of methane on both Li-doped MgO and pure MgO
catalysts.
Highlights
• The multi-scale approach of UNICAT to the oxidative coupling of methane
made substantial achievements for the fundamental understanding of
simplest OCM catalyst and the development of promising catalyst and
process for industrial application.
• Revision of the long-time established “Lunsford”-mechanism
• Detailed understanding of the contribution of gas phase reactions
• Proposal of new activation mechanism at non-reducible oxide surfaces
• Revealing of fluctuations in composition and shape of catalyst surface by
in-situ structural studies at model systems
• Substantial improvement of mixed hetero-metallic NaMnSi oxide catalyst
by advanced preparation methods
• Identification of different oxygen species involved in selective and in
selective reaction pathways
• Development of optimized reactor concepts on the basis of
comprehensive kinetic models
• Conception and validation of new OCM process on mini-plant level
• Measurements for differently prepared pure MgO catalysts suggest
that the catalytic activity originates from morphological defects.
• The activity proved to be very different in the initial phase of the OCM
reaction and in the steady state.
• Substantial morphological changes and restructuring of the
terminations as transmission electron microscopy revealed.
Modes of dynamics in catalysis with novel
aspects of chemical and structural dynamics
0h
66 h
• New mechanism proposed:
Methane binds heterolytically on Mg2+O2- sites at steps
and corners, and methyl radicals are released into the
gas phase when O2 is present on the surface.
• The role of the catalyst surface is to bind CH4 and O2
which exchange redox equivalent directly among
themselves, but not with the catalyst.
Kwapien, Paier, Sauer, Geske, Zavyalova, Horn, Schwach, Trunschke, Schlögl, Angew. Chem. Int. Ed., 2014, 53, 8774
Kinetic Investigations of Gas Phase Reactions
Activation of O2 at model catalysts
Highlights
Highlights
• Charge transfer from Mo donor ions stimulates the formation
of superoxo-species on the surface of a wide-gap CaO film.
• Formation of pre-dissciated O2- species
• Final dissociation via electron tunneling from STM tip
A profile reactor with on-line MS analysis allows spatial
resolution of reactant and product concentrations in catalyst
beds as well as free gas phase
• Coupling of methane to C2-products without catalysts
• Lag period for establishment of radical pool
• Strong pressure dependence of selectivity
Objectives and strategys
• Characterize different oxygen species on the catalyst surface
by joint experimental – computational work
• Use computational methods to explore the role of different
oxygen species in the complex reaction mechanism
Objectives
Extention of profile reactor studies to other hydrocarbon oxidation
reactions and combination with in-situ studies of catalyst surface
• Microkinetic model for homogeneous gas phase reactions
• Two dimensional reactor modeling with CFD tool for model
validation
R. Horn, O. Korup, M. Geske, U. Zavyalova, I. Oprea, R. Schlögl , Review of Scientific Instruments 2010, 81, 64102
Cui, Shao, Baldowski, Sauer, Nilius Freund, Angew. Chem. Int. Ed., 2013, 52, 11385
Synthesis of Mn/Na2WO4/SBA-15
Objectives
precatalyst
silica
support
Reactor concepts
catalyst
Highlights
• Investigation of structural dynamics
• Correlation of performance and
dynamics
commercial
• Identification of tuning parameters
for dynamic properties
Impregnation
Calcination
Na2WO4 · 2 H2O
Mn(ac)2 ·4 H2O
• Comparison of phase pure and
complex phase catalysts
750°C
• Detailed mechanistic studies and kinetic modeling of OCM
• Simulation studies for OCM in Fixed Bed, Fluidized Bed and
Membrane Reactor
• Derivation of optimized feed strategies
• Validation of catalysts performance with up to 200 g catalyst
• C2-Yield of 25,5 % at 80 % selectivity
• Concepts for integrated OCM/DRM reactor
X
Mn-Na2WO4/SBA-15
Scheme of fluidized bed reactor and OCM performance data
Mn-Na2WO4/SBA-15
S. Jaso et al., J. Nat. Gas Chem., 2012, 21 534-543
nanostructured
(SBA-15)
Mn-Na2WO4/
commercial silica
Up-scaling of catalyst synthesis
Highlights
Objectives
• Design of reactors and operation
strategies by simulation studies with
comprehensive kinetic models
• Highly homogeneous dispersion of active components over SBA-15
• Increased activity due to higher dispersion of Mn/Na2WO4
• Increased selectivity due to reduced number of non-selective sites at
uncovered support material
• Improved stability
Testing on lab scale C2-Yield= 12 %
Validation in Miniplant C2-Yield= 25,5 %
M. Yildiz, Y. Aksu, U. Simon, K. Kailasam, O. Goerke, F. Rosowski, R. Schomäcker, A. Thomas, S. Arndt Chem. Commun. 2014, 50, 14440
Process Design and Validation in Mini-Plants
• Design and optimization of membrane
fluidized bed reactor
Scheme of membrane reactor and performance data
H. R. Godini, et al. Energy & Fuels 2013, 1312
• Utilization of instationary operation
conditions
Harnessing the Methodological Toolbox
Highlights
Objectives
Physical methods for structure analytical studies
New Reactor concepts
• Successful scale-up of OCM to a mini-plant
• Yield of 25,5 % at 80 % selectivity in mini-plant
• 50 % energy saving in down-stream processing by hybrid
separation process
• Concepts for process integration of OCM and DRM
• Investigation of different equipment alternatives
• Chemical Microscope EMIL
• Dynamic behavior of reactors under recycle conditions
• Vibrational spectrodscopy for identifying adsorbates
• Chemical Looping for partial oxidation
reactions
• Integration of reactors with instationary operation mode
• EPR spectroscopy for high spin metal centers
• Solid-state NMR with dynamic nuclear polarization (DNP)
• X-Ray adsorption spectroccopy for direct tracking of structural changes
Conventional design of
OCM process
Steam
Generator
Refrigerant
Compressor
Reactor
CO2
Absorption
Cryogenic
Distillation
CO2
CH4, CO, H2
Reactor
Compressor
Air Blower
Steam
Generator
Adsorptive
Separation
CO2
Absorption
CH4, CO, H2
CO2
• Challenges for fluid dynamics and process
control
C2
C2
Scheme of alternative OCM process without compressor
D2/E2
• Feed strategies for separation of competitive
reactions
Flow diagram of new OCM process
H. R. Godini, et.al. Technical Transactions 2012, 5, 63–74
Dynamical terminating graphene layer at bulk copper metal
(green lines in right image) followed by the home-developed
in-situ ambient pressure SEM.
Scheme of Chemical Looping operation
of fixed bed reactors