PNNL

Abstract

A portion of this work was conducted at EMSL, a national scientific user facility. Electronic structure calculations based on Density Functional Theory (DFT) are increasingly used to probe reaction mechanisms on catalyst surfaces. These calculations provide information about geometries, stabilities, and reactivities of adsorbed species on various surfaces. Conducting microkinetic analysis in conjunction with DFT calculations forms a powerful combination of methodologies to allow quantitative information to be derived about catalytic reactions at the molecular level. Specifically, whereas the microkinetic approach does not make any a priori assumptions about which steps may be rate controlling or which species may be abundant on the surface, there is usually not sufficient information to extract values of all kinetic parameters from experimental data. In contrast, results from DFT calculations alone cannot be used to assess the relative rates of various pathways, because these rates depend on reaction conditions. Instead, the results from DFT calculations form initial estimates of parameters for the microkinetic model, and the microkinetic model is used to predict rates of elementary steps and surface coverages under various reaction conditions, thereby forming a bridge with reaction kinetics data and surface spectroscopic measurements. In this paper, we outline some of the concepts useful for understanding DFT calculations and for using the results of these calculations in reaction modeling. We also introduce key concepts in microkinetic analysis, and we illustrate how microkinetic models are used to probe reaction pathways, reaction orders, and surface coverages for the decomposition of methanol on platinum.