Computational Investigation of the Thermochemistry and Kinetics of Steam Methane Reforming Over a Multi-Faceted Nickel Catalyst

A microkinetic model of steam methane reforming over a multi-faceted nickel surface using plane-wave, periodic boundary condition density functional theory is presented. The multi-faceted model consists of a Ni(111) surface, a Ni(100) surface, and nickel step edge sites that are modeled as a Ni(211) surface. Flux and sensitivity analysis are combined to gain an increased understanding of the important reactions, intermediates, and surface facets in SMR. Statistical thermodynamics are applied to allow for the investigation of SMR under industrially-relevant conditions (e. g., temperatures in excess of 500 degrees C and pressures in excess of 1 bar). The most important surface reactions are found to occur at the under-coordinated step edge sites modeled using the Ni(211) surface as well as on the Ni(100) surface. The primary reforming pathway is predicted to be through C* + O* -> CO* at high temperatures; however, hydrogen-mediated reactions such as C* + OH* -> COH* and CH* + O* -> CHO* are predicted to become more important at low temperatures. The rate-limiting reactions are predicted to be dissociative chemisorption of methane in addition to the aforementioned C-O addition reactions.