Activation and deactivation of Ag/CeO2 during soot oxidation: influences of interfacial ceria reduction

Different Ag/CeO2 catalysts with uniform structures and diverse surface oxygen vacancy (VO-s) contents were synthesized via a modified solution combustion method. Based on the results of Raman spectroscopy, H-2-TPR and isothermal soot oxidation, it was suggested that even with gaseous O-2 participating in the reaction, ceria surface sites around the catalyst-soot contact points can still be reduced by soot gradually. This interfacial reduction led to the generation of extra VO-s without changing the oxygen vacancies in the bulk of CeO2. Notably, this VO-s dynamic change and the insufficient O-2 (-) regeneration/delivery further resulted in the activation and deactivation of Ag/CeO2 during reaction with soot. This means that both the existence of ceria VO-s and its dynamic change during reaction may have a crucial influence on catalyst behavior. By further exploring these activity variations, the VO-s content, catalyst-soot contact condition and extra oxygen supplier were proved to be the three most important structural factors behind the soot oxidation activity of all the ceria-based catalysts. In this sense, Ag/CeO2 catalysts with appropriate morphology and moderate initial VO-s content may exhibit good activity for soot oxidation.