Synergistic Catalysis of Carbon Monoxide Oxidation over Copper Oxide Supported on Samaria-Doped Ceria

Copper oxide supported on samaria-doped ceria (SDC) is chosen as a model catalyst for carbon monoxide oxidation to illustrate interfacial metal oxide–support interaction and synergism. The oxidation catalysis by CuO/SDC was studied to further elucidate the effect of oxygen vacancies on activity enhancement and light-off behavior. It was found that an approximate proportionality exists between the reducibility and the activity of catalysts. It is concluded that reducibility and susceptibility of change of oxidation states of copper oxides is key to catalytic activities, and the nonstoichiometric metastable copper oxide species formed during reduction are very active because of their superior capability to transport surface lattice oxygen. A preliminary mechanism involving surface lattice oxygen of CuO and oxygen vacancy participation is proposed to fully explicate the synergistic process leading to light-off. The cause of light-off is attributed to the formation of co-shared oxygen ions coupled with the creation of high-turnover-frequency active sites which are composed of metastable copper oxide species and oxygen vacancies of two types, Vo,CuO and Vo,SDC. Over these CuO/SDC catalysts, the active sites exhibit the Langmuir–Hinshelwood-type mechanism characteristic of precious metals although the redox-cycle mechanism is still operative.