(38b) A DFT+U and Ab Initio Thermodynamics Approach to Hydrocarbon Oxidation Mechanism Determination on Oxide Catalysts: Propane Oxidation on Zr-Doped CeO2

Elucidation of the elementary reaction processes involved in hydrocarbon oxidation on oxide catalysts can help guide active site optimization. This talk will discuss the difficulties and approaches developed for considering the complex elementary mechanism of propane oxidation over metal oxide catalysts.  We use density functional theory (DFT+U) methods to examine the reforming of propane over the Zr-doped CeO₂ (1 1 1) surface. Numerous modeling and mechanistic questions arise in modeling this multistep reaction on oxides. The surface redox and coverage state in the reaction environment impacts energetics and must be considered. Phase diagrams of Zr-doped and pure CeO₂ (1 1 1) are created based upon the partial pressure of oxygen and hydrogen, demonstrating that the surface will be reduced under operating conditions. All elementary energetics along the preferential path for propane reforming were identified, and differences in path with oxygen pressure variance were identified. The reaction path varies depending on the oxygen chemical potential, as this alters at which step in the mechanism the surface will re-oxidize.  The use of the stoichiometric oxide surface as the reactive surface for propane oxidation is found to misrepresent the reaction energetics and path, as the stable surface under propane reforming conditions is highly reduced.