CO Oxidation Promoted by a Pt 4 /TiO 2 Catalyst: Role of Lattice Oxygen at the Metal/Oxide Interface

CO oxidation promoted by a subnano Pt 4 cluster deposited on the anatase a-TiO 2 (101) surface has been investigated by means of DFT + U calculations. The focus of the study is on the role of supported Pt 4 in favoring the formation of an oxygen vacancy at interface sites between Pt 4 and the TiO 2 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 TiO 2 where the reaction involves O 2 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 Pt 4 and TiO 2 , 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 CO 2 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-TiO 2 (101) surface. The next step consists in the re-oxidation of the support. The calculations show that the O 2 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. Graphical Abstract: [Figure not available: see fulltext.].