CO Oxidation Promoted by a Pt4/TiO2 Catalyst: Role of Lattice Oxygen at the Metal/Oxide Interface

Abstract

CO oxidation promoted by a subnano Pt4 cluster deposited on the anatase a-TiO2(101) surface has been investigated by means of DFT + U calculations. The focus of the study is on the role of supported Pt4 in favoring the formation of an oxygen vacancy at interface sites between Pt4 and the TiO2 surface, a key step in CO oxidation reactions according to a Mars–van Krevelen mechanism. The motivation is to compare this reaction mechanism with other processes described in the literature for Pt clusters on anatase TiO2 where the reaction involves O2 dissociation at the surface of the metal particle or its activation at the metal/oxide interface. A significant decrease in the energetic cost to remove a lattice oxygen is observed at the interface sites between Pt4 and TiO2, compared to regular sites. This favors the CO oxidation processes by a direct interaction of the CO molecule with a lattice oxygen, with formation of CO2 and an oxygen vacancy. The processes is slightly endothermic, and occurs with barriers comparable, or even lower, than found for the case of Au nanoparticles supported on the same a-TiO2 (101) surface. The next step consists in the re-oxidation of the support. The calculations show that the O2 molecule adsorbs strongly on the reduced catalyst, dissociates with one O atom that recreates the stoichiometric surface, and the other that remains adsorbed on the surface, ready to react with a second CO molecule.