Surface adsorbed and lattice oxygen activated by the CeO2/Co3O4 interface for enhancive catalytic soot combustion: Experimental and theoretical investigations

Abstract

Metal oxide-oxide interface on supported catalyst has been rarely studied due to the complex interfacial structure and synthetic challenge. Herein, different Ag-supported CeO2/Co3O4 samples with various covered-state of CeO2 were prepared for catalytic soot oxidation. In comparison, catalytic activity was significantly improved by grafting CeO2 on Co3O4, in which the best performing Ag/CoCe-2 exhibited remarkable catalytic performance towards soot oxidation with a T50 of 290.5 ℃ under 10 % O2/N2. Catalyst characterization investigated by Scanning Electron Microscope (SEM), quasi in-situ X-ray Photoelectron Spectroscopy (XPS), in-situ Raman, etc. revealed that this outstanding promotion in catalytic activity can be principally ascribed to the formation of the CeO2/Co3O4 interface. An appropriate CeO2 dosage maximized the contact and interaction between Co3O4 and CeO2, resulting in the largest CeO2/Co3O4 interface featured with abundant generated superoxide species and activated surface lattice oxygen. Density functional theory (DFT) calculations were also carried out for the oxygen vacancy formation energy, Gibbs free energy, etc. In presence of the CeO2/Co3O4 interface, a charge density redistribution around the adsorbed reactants at oxygen vacancies could be formed, owing to the efficient charge transfer enhanced by the electron-appealing effect. The change in electronic structure favored reducing the oxygen vacancy formation energy and boosting the lattice oxygen activation induced by the hybridized Co-O-Ce bonds, finally lowering the adsorption and activation barriers for reactive species and accelerating the reaction kinetics.