Density Functional Theory-Assisted Microkinetic Analysis of Methane Dry Reforming on Ni Catalyst

A comprehensive microkinetic model based on density functional theory (DFT) calculations is constructed to explore the reaction mechanism for dry methane reforming on Ni catalyst. Three low-index facets, namely, Ni(111), Ni(100), and Ni(211), are utilized to represent the contributions from the flat, open, and stepped surfaces. Adsorption energies of all the possible reaction intermediates as well as activation energies for the elementary reactions involved in dry reforming of methane on the three Ni surfaces are calculated through DFT. These results are further employed to estimate the rate constants for the elementary reactions under realistic temperatures and pressures within the framework of transition state theory and statistical mechanics treatments. The dominant reaction pathway is identified as CH4 successive dissociation followed by carbon oxidation by atomic oxygen. The dependence of the rate-determining step on operating conditions is examined. At low CH4 and CO2 partial pressures, both CH4 dissociative adsorption and carbon oxidation would jointly dominate the overall reaction rate, while at high pressures carbon oxidation is suggested as the rate-determining step for the DRM reaction. Our findings provide a rational interpretation of contradictory experimental observations.