Investigation of Cu-doped ceria through a combined spectroscopic approach: Involvement of different catalytic sites in CO oxidation.

Copper-ceria mixed oxides are widely considered promising catalysts for oxidation reactions, especially when the participation of lattice oxygen is required. However, the mechanistic understanding of these catalytic systems is still incomplete, due to their considerable complexity. In fact, copper doping of ceria results in the formation of a significant number of different interacting sites in continuous evolution during the catalytic processes. In the present study, pure and Cu-doped ceria samples were deeply investigated through combined spectroscopic techniques, i.e. XPS, EPR, and in situ FTIR and Raman spectroscopy. Through this systematic approach, the copper sites and lattice defects responsible for the enhanced CO oxidation activity of doped ceria were elucidated. Superficial Cu+ species and small Cu0 clusters promote the adsorption of CO at low temperature, while isolated Cu2+ monomers and dimers well-dispersed in the ceria matrix foster lattice oxygen mobility, involving the sub-surface in the redox phenomena. Consequently, the structure of Cu-doped ceria undergoes substantial modifications throughout CO oxidation in the absence of O 2 , with the formation of oxygen vacancy clusters. Anyway, these changes are reversible, and structural reorganization in the presence of O 2 can occur even at room temperature. The excellent performance of Cu-doped ceria eventually stems from the effective cooperation among the different catalytic sites in the mixed oxide. [Display omitted] • The different defects and Cu sites in doped ceria are complementarily investigated. • Cu+ sites and small Cu0 clusters at the catalyst surface enhance CO adsorption. • Isolated Cu2+ monomers and dimers in the CeO 2 matrix foster lattice oxygen mobility. • Clusters of oxygen vacancies may form when the oxygen demand at the surface is high. • The effective cooperation of the different sites promotes ceria catalytic activity. [ABSTRACT FROM AUTHOR]