Enhanced Ammonia Synthesis Activity of Ceria-Supported Ruthenium Catalysts Induced by CO Activation

Metal–support interactions strongly affect the catalytic performances of ceria-supported metal catalysts, and hydrogen treatment at high temperature is important for the preparation of catalysts that show strong metal–support interaction (SMSI). With SMSI, the proportion of metal species existing in the form of a metallic state is lowered, consequently hindering the performance of a metal catalyst for a reaction that requires metallic sites. Here we show that CO activation of a Ru/CeO 2 catalyst not only enhances the reduction degree and exposure of Ru species but also increases Ce 3+ concentration, oxygen vacancy (O V ), and active oxygen, resulting in the formation of electron-enriched Ru δ− species and Ru δ− –O V –Ce 3+ sites. As a result, a Ru/CeO 2 catalyst after CO activation shows high ammonia synthesis activity, and the ill effect of hydrogen poisoning is effectively alleviated. These findings are important for the design of supported metal catalysts that afford metallic species as active sites.