Defective outermost layers of ceria catalysts determined by electrochemical methods as direct responsible for catalytic activity in total oxidation of a representative VOC

A large set of unsupported ceria catalysts has been synthesized, physicochemical and electrochemically characterized, and tested in a representative catalytic reaction (total oxidation of a volatile organic compound-VOC, propane). Interestingly, in spite of the diverse synthesis procedures employed, a clear relationship between the electrochemical properties of the active surface layer (related with the amount of oxygen vacancies) and the catalytic activity in the total oxidation of VOCs has been observed. Then, the resistance to the charge transfer in the outer layer of the catalysts (depth of ca. 1.5 nm), which is inversely related to the amount of oxygen vacancies in that range, clearly determines the catalytic activity in the total oxidation. If the near surface is considered (outer than 10 nm, observed by XPS) a poor relationship can be appreciated. However, if the whole bulk of the cerias (overall resistance) is considered, this electrochemical-thermocatalytic relationship is not observed.