Understanding Surface Catalyzed Decomposition Reactions Using a Chemical Pathway Analysis

Abstract

A theoretical microkinetic model is developed to describe the decomposition of methanol into formaldehyde, carbon monoxide, and hydrogen on eight transition metal surfaces using density functional theory (DFT) calculations and transition state theory (TST). The chemical kinetics are then analyzed using a recently developed technique, the sum over histories representation (SOHR), that clearly reveals the chemical pathways followed by the system. The model itself consists of 10 reversible hydrogen abstraction reactions as well as the adsorption–desorption of methanol, formaldehyde, hydrogen, and carbon monoxide. The computed rate coefficients are fit to generalized Arrhenius expressions that are applicable to a wide range of conditions. While the lateral interactions are not explicitly computed, the effects of surface coverage are included using a site-blocking model for the kinetics. The SOHR method allows the chemical pathways followed by the surface species to be determined and weighted by unique probabilities. Locating the most probable chemical pathways is very useful in understanding the selectivity of product formation and can be used to determine the “optimal” reaction conditions.