Computer Generated Microkinetic Mechanisms: Applications for Catalytic Combustion of Methane on Pt

Many processes for methane activation are performed at high temperatures and pressures, such as catalytic partial oxidation, [1] catalytic combustion, [2] and oxidative coupling.[3] Under these conditions, the heterogeneous surface kinetics can be coupled with homogeneous gas-phase chemistry. Creating a homogeneous/heterogeneous coupled mechanism that is based upon elementary reactions and is thermodynamically consistent is a major challenge in modeling and analysis of chemical reactors under industrial conditions. In most instances, either the surface or the gas-phase chemistry is treated in an ad hoc manner. Important pathways may be neglected, and the mechanism my violate fundamental principles of thermodynamics.

In this talk, we present a new tool for generating microkinetic mechanisms in heterogeneous catalysis, RMG-Cat.[4] RMG-Cat previously has been applied successfully to methane dry reforming on Nickel. In the present work, RMG-Cat was expanded to include methane oxidation on Platinum as well. Additionally, the new RMG-Cat can seamlessly handle both gas-phase and surface chemistry within a self-consistent, unified framework.

To demonstrate the new functionality of RMG-Cat, we look at recent high-temperature experimental data for the catalytic combustion of methane on a Pt gauze.2 RMG-Cat successfully generated a mechanism that includes bond fission and abstraction reactions on the catalyst surface, radical-driven chemistry in the gas phase, and adsorption/desorption kinetics for the coupling between the two regimes. The resulting mechanism ensures thermodynamic consistency by providing the rate coefficient for each reaction in a single direction and then computing the equilibrium constant from temperature-dependent free energies for gas-phase and surface intermediates.

[1] Korup, O., Goldsmith, C. F., Weinberg, G., Geske, M., Kandemir, ., Schlogl, R., Horn, R. “Catalytic partial oxidation of methane on platinum investigated by spatial reactor profiles, spatially resolved spectroscopy, and microkinetic modeling” Journal of Catalysis (2013) 297, 1-16

[2] Scwartz, H., Dong, Y., Horn, R. “Catalytic Methane Combustion on a Pt Gauze: Laser-Induced Fluorescence Spectroscopy, Species Profiles, and Simulations” Chem. Eng. Technol. (2016) 39, 2011-209

[3] Karakaya, C., Kee, R. J. “Progress in the direct catalytic conversion of methane to fuels and chemicals” Prog. Energy Comb. Sci (2016) 55, 60-97

[4] Goldsmith, C. F., West, R. H. “Automatic Generation of Microkinetic Mechanisms for Heterogeneous Catalysis” J. Phys. Chem. C. http://doi.org/10.1021/acs.jpcc.7b02133