Seminars Archive

Ab-initio thermodynamics and adsorption properties of platinum oxides

Abstract
Aim of the presented work is to understand which platinum/platinum oxide phases could play a role in catalytic converters for oxidation of hydrocarbons under oxygen-rich conditions. The computational methods employed are based on the density-functional theory and are extended to non-zero temperatures and pressures through the first-principles atomistic thermodynamics. Thermodynamic stability of bulk platinum oxides has been examined by calculating their free energies of formation and a phase diagram for bulk oxides has been obtained in dependence of oxygen pressure and temperature. α-PtO2 has been found to be the stable oxide at low temperatures, at high temperature metallic Pt is stable and at intermediate temperatures there is a region of stability of Pt3O4. Bulk oxide surfaces and oxide thin films on Pt(111) and Pt(100) up to a few monolayers have then been considered. On the thermodynamically (meta-)stable surface structures dissociative adsorption of methane has been simulated. While on Pt(111) a rather inert α-PtO2 monolayer is expected to form, on Pt(100) a competition between a PtO-like and a Pt3O4-like oxide is predicted. Latter oxide grows epitaxially on Pt(100); on it the dissociative adsorption of methane is most exotermic and both H and CH3 adsorb preferentially on the surface oxygens.