Computational Investigation of Thermochemistry and Kinetics of Steam Methane Reforming on Ni(111) under Realistic Conditions

The reaction pathways and kinetics of steam methane reforming (SMR) over Ni(111) are investigated using plane wave density functional theory. The thermochemical data are used to develop a microkinetic model of SMR that allows for the investigation of reforming pathways and the most abundant reaction intermediates on the catalyst surface at industrially relevant temperatures and pressures. Pairing the kinetic model with a statistical thermodynamic treatment, surface behavior under a wide range of temperatures, pressures, and initial concentrations can be examined. We present our results at T = 800 degrees C and P = 10 bar with an initial H2O/CH4 ratio of 2.5:1. Sensitivity analysis is used to provide information about rate-limiting steps in the reaction network. The reaction intermediate CH* is found to be the most important carbon-containing intermediate. CH4(g) adsorption as well as the reactions CH* + O* -> CHO* and CH* + OH* -> CHOH* are found to be the most sensitive reactions in the mechanism. Consistent accounting for entropic effects was found to be important in obtaining reasonable surface coverages of reaction intermediates, which can influence the determination of active reforming pathways on the catalyst surface.