1. Selective Oxidation of C-H Bonds Raw Materials Change in Chemical Industry and Efficient Energy Storage
Introduction
Model studies of C-H Activation
Objectives and strategy
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
Highlights
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.
0 h
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.
Modes of dynamics in catalysis with novel
aspects of chemical and structural dynamics
Kwapien, Paier, Sauer, Geske, Zavyalova, Horn, Schwach, Trunschke, Schlögl, Angew. Chem. Int. Ed., 2014, 53, 8774
Activation of O2 at model catalysts
Kinetic Investigations of Gas Phase Reactions
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
Highlights
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
Reactor concepts
Objectives
Investigation of structural dynamics
Correlation of performance and dynamics
Identification of tuning parameters for dynamic properties
Comparison of phase pure and complex phase catalysts
Highlights
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
silica support
pre-catalyst
catalyst
commercial
Impregnation
Calcination
Na2WO4 · 2 H2O
750°C
Mn(ac)2 ·4 H2O X
Mn-Na2WO4/SBA-15
Mn-Na2WO4/SBA-15
Scheme of fluidized bed reactor and OCM performance data
S. Jaso et al., J. Nat. Gas Chem., 2012,
nanostructured (SBA-15)
Mn-Na2WO4/
commercial silica
Up-scaling of catalyst synthesis
Objectives
Design of reactors and operation strategies by simulation studies with comprehensive kinetic models
Design and optimization of membrane fluidized bed reactor
Utilization of instationary operation conditions
Highlights
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 %
Scheme of membrane reactor and performance data
M. Yildiz, Y. Aksu, U. Simon, K. Kailasam, O. Goerke, F. Rosowski, R. Schomäcker, A. Thomas, S. Arndt Chem. Commun. 2014, 50, 14440
H. R. Godini, et al. Energy & Fuels 2013, 1312
Harnessing the Methodological Toolbox
Process Design and Validation in Mini-Plants
Highlights
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
Physical methods for structure analytical studies
Chemical Microscope EMIL
Vibrational spectrodscopy for identifying adsorbates
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
New Reactor concepts
Chemical Looping for partial oxidation reactions
Feed strategies for separation of competitive reactions
Challenges for fluid dynamics and process control
Objectives
Investigation of different equipment alternatives
Dynamic behavior of reactors under recycle conditions
Integration of reactors with instationary operation mode
Conventional design of
OCM process
Steam Generator
Refrigerant Compressor
Reactor
Compressor
CO2 Absorption
Cryogenic Distillation C2
CO2
CH4, CO, H2
Air Blower
Steam Generator
Reactor
Adsorptive Separation
CO2 Absorption C2
Dynamical terminating graphene layer at bulk copper metal
(green lines in right image) followed by the home-developed
in-situ ambient pressure SEM.
CH4, CO, H2
CO2
Flow diagram of new OCM process
Scheme of Chemical Looping operation
of fixed bed reactors
Scheme of alternative OCM process without compressor
H. R. Godini, et.al. Technical Transactions 2012, 5, 63–74
D2/E2