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

Abstract

Different Ag/CeO₂ catalysts with uniform structures and diverse surface oxygen vacancy (V_O-s) contents were synthesized via a modified solution combustion method. Based on the results of Raman spectroscopy, H₂-TPR and isothermal soot oxidation, it was suggested that even with gaseous O₂ 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 V_O-s without changing the oxygen vacancies in the bulk of CeO₂. Notably, this V_O-s dynamic change and the insufficient O₂⁻ regeneration/delivery further resulted in the activation and deactivation of Ag/CeO₂ during reaction with soot. This means that both the existence of ceria V_O-s and its dynamic change during reaction may have a crucial influence on catalyst behavior. By further exploring these activity variations, the V_O-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 V_O-s content may exhibit good activity for soot oxidation.