Dynamic monte carlo simulations of catalytic surface reactions

Abstract

A general-purpose program for dynamic Monte Carlo (DMC) simulations of catalytic surface reactions has been developed. The stochastic model is based on the master equation. Inputs for the program are the catalytic surface, the adsorbates, the elementary reaction steps, and the adsorbate-adsorbate interactions, which can be defined for a variety of systems. The computer code is especially applicable to structured surfaces, which can be defined as bitmap by common drawing software. Dissociative or non-dissociative adsorption, associative or single desorption. Langmuir-Hinshelwood and Eley-Ridel reactions as well as surface diffusion can be used in the surface reaction mechanism. The performance of the algorithm is optimized by a combination of two different solution methods. We present three example models, all of them showing a strong connection between surface structures and chemical reactions: inhomogenities on Pt(111) may act as nucleation centers either for the formation of CO or oxygen islands during kinetic phase transitions of CO oxidation. Model calculations reproduce experimentally observed structure formation at ultra high vacuum conditions. Adsorbate-induced changes of the surface structure leads to spatiotemporal pattern formation during CO oxidation on Pt(100) and Pt(110). DMC simulations based on the reconstruction model generate target pattern and cellular structures similar to experimental findings. A common class of real catalysts consist of nanoparticles deposited on a support. Mechanistic steps on facet boundaries of supported nanoparticles significantly influence the catalytic behavior. DMC calculations can be used to simulate different scenarios to get an insight into the principles of real catalysts.