Simon Podkolzin - Monte Carlo Simulations of Reaction Kinetics for Ethane Hydrogenolysis over Pt

Monte Carlo Simulations of Reaction Kinetics for Ethane Hydrogenolysis over Pt.

Simon G. Podkolzin; Rafael Alcala; Juan J. de Pablo; James A. Dumesic

Journal of Physical Chemistry B 106(37), 9604-9612 (2002)

Link to publication details on publisher's server

Abstract

A Monte Carlo (MC) molecular model, with parameters derived from density functional theory calculations, is used to describe experimental data for the rate of ethane hydrogenolysis for a Pt/SiO₂ catalyst over a wide range of conditions. The surface concentrations of the most abundant stable species (hydrogen atoms, ethylidyne species, and di-s-bonded ethylene) are simulated with a MC grandcanonical ensemble, and the rate of ethane hydrogenolysis is calculated by simulating surface concentrations for three types of transition state complexes for C-C bond cleavage. The simulation shows that larger repulsive interactions between adsorbed C₂H_x and H species lead to more negative reaction orders with respect to the hydrogen pressure. The results of the MC simulation indicate that the reaction proceeds primarily through C-C bond cleavage in adsorbed C₂H₅ species, with smaller contributions from adsorbed CHCH₃ and CHCH₂ species. The MC results suggest that although the most abundant surface hydrocarbon species has a stoichiometry of C₂H₃, the reaction proceeds through more highly hydrogenated C₂H₅ species. The state of the surface is predicted to change from being primarily hydrogen-covered at most experimental conditions to being highly hydrocarbon-covered at low hydrogen partial pressures.

Address:

Department of Chemical Engineering, University of Wisconsin, Madison, WI 53706, USA.

Publisher:

American Chemical Society

CODEN: JPCBFK, ISSN: 1520-6106, CAN 137:310546, AN 2002:644466

Animation of DFT calculations and Monte Carlo simulations

	Surface sites on (111) surface plane: atop, bridge and three-fold. Hexagonal lattice model slab. A small unit cell (2x2, 2x3 or 3x3) with periodic boundary conditions was used in DFT calculations, and a larger (42x42) periodic unit cell was used in Monte Carlo simulations with a lattice gas model. More information on modeling CO adsorption. More information on modeling ethylidyne (C-CH₃) and hydrogen co-adsorption.
	Monte Carlo trial moves in modeling co-adsorption of ethane and hydrogen with the formation of ethylidyne (C-CH₃) and atomic hydrogen surface species: 1) ethane dehydrogenation into ethylidyne and hydrogen, 2) adsorption of the formed species, 3) hydrogen dissociation, 4) adsorption of atomic hydrogen, 5) surface diffusion of ethylidyne and hydrogen species, 6) desorption. More information on modeling ethylidyne (C-CH₃) and hydrogen co-adsorption.
	Monte Carlo trial moves for insertion, removal and diffusion of ethylidyne (C-CH₃) and hydrogen surface species. More information on modeling ethylidyne (C-CH₃) and hydrogen co-adsorption.
	Monte Carlo trial moves for kinetic modeling of ethane hydrogenolysis. The pseudo steady-state background is determined by co-adsorption of ethylidyne (C-CH₃), hydrogen and di-s-bonded ethylene surface species. The reaction rate is calculated using virtual insertion trial moves for identified 3 transition state species: C₂H₅^‡, CH-CH₃^‡ and CH-CH₂^‡.
	Transformation of di-s-bonded ethylene (on a bridge site) to a more stable ethylidyne species and surface hydrogen. More information on ethylene adsorption on supported Pt. More information on ethylene adsorption on supported Pt-Au. More information on acetylene hydrogenation with ethylene formation on Pt(111).

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