Density functional theory studies of doped ceria systems: Alkane oxidation and desulfurization

Efficient utilization of hydrocarbon feedstocks involves removal of potential pollutants and catalyst poisons such as H ₂S, as well as catalysis of hydrocarbon oxidation to produce energy. For example, gasification of biomass has the potential to provide a method for the conversion of a renewable feedstock to usable fuels, however efficient cleanup of biomass-derived syngas involves removal of H ₂S, reforming of remaining light hydrocarbons such as "slip" methane, and tar hydrogenolysis/reforming at high temperature (>850 K). Ceria exhibits activity for the oxidation of hydrocarbons and adsorption of H ₂S, making it potentially suitable for both catalytic combustion applications as well as a desulfurization sorbent. Ceria-based metal oxides are stable at high temperatures, and the sulfur adsorption capacity and C-H activity of ceria can be altered by the addition of other rare earth or transition metals. Our work applies density functional theory (DFT+U) methods to evaluate the surface chemistry of doped ceria surfaces for hydrocarbon conversion and H ₂S absorption. Elementary step energetics are used to interpret experimentally observed trends in C-H activation activity and sulfur adsorption capacity, as well as to predict optimal doped ceria compositions and structures.