The influence of ceria on Cu/TiO2 catalysts to produce abundant oxygen vacancies and induce highly efficient CO oxidation

Abstract

Ce and Cu species deposited on TiO₂ (CuCe_x/TiO₂) are employed as catalysts for CO oxidation. The CuCe_x/TiO₂ catalysts can apparently provide a higher turnover frequency (TOF) rate and lower activation energy than a Cu/TiO₂ catalyst without a Ce additive. Compared to a CuCe/SiO₂ catalyst, TiO₂ as a catalyst support can promote a high surface ratio of Cu/Ce and the formation of small CeO₂ particles on the Cu/TiO₂ catalysts. The presence of a Cu–CeO₂ interaction on the CuCe_x/TiO₂ catalysts may increase the likelihood of an increase in the concentration of Ce³⁺ species and an abundance of oxygen vacancies with the CeO₂ particles. The abundance of oxygen vacancies on the CuCe_x/TiO₂ catalysts may result in a high catalytic rate for CO oxidation. Furthermore, the oxygen vacancies can significantly activate the oxygen reactant, thus acting as an oxygen supplier and further catalyzing CO oxidation. The activated oxygen molecule can form active oxygen and/or lattice oxygen to oxidize CO on the Cu surface. On the other hand, a bidentate formate intermediate generated from CO adsorbed on the CuCe_x/TiO₂ surface is also an important factor for high CO oxidation activity. Adsorbed CO at an interface between Cu and CeO₂ can combine with nearby active oxygen to form a bidentate formate intermediate that can react with CO to form CO₂. In this work, catalyst characterization was performed and reaction kinetics and reaction mechanisms were investigated and correlated to the reaction rate of CO oxidation.