Synergistic effect of Cu on a Ag-loaded CeO₂ catalyst for soot oxidation with improved generation of active oxygen species and reducibility

In this work, the promoting effects of Cu on Ag-loaded CeO₂ catalysts on soot oxidation were investigated through a series of Cu-incorporated catalysts (AgCu(x)Ce) with various amounts of Cu. Ag particles were highly dispersed over Cu(x)Ce mixed oxide, and AgCu(x)Ce catalysts presented improved activity in comparison to Ag/CeO₂. Raman spectra and H₂-TPR showed that the complex effects of the Ag-CeO₂ and CuO-CeO₂ interactions enhanced the ability to generate highly active superoxide (O₂⁻) and greatly improved the reducibility of AgCu(x)Ce catalysts. The amount of Cu affected degrees of both the Ag-CeO₂ and CuO-CeO₂ interactions, and consequently, the ratio of active oxygen species (O_xⁿ⁻) and the reducibility of the catalysts varied. AgCu(0.4)Ce with adequate surface oxygen vacancies promoted the generation of O₂⁻, and the promoting effects enhanced the reducibility, resulting in greatly improved activity. It is suggested that introduction of Cu to Ag/CeO₂ significantly improves the activity of the catalyst and that the optimized Cu content induces positive interrelations, whereas excessive Cu hinders the improvement in catalytic performance due to decreased synergistic effects between the Ag-CeO₂ and CuO-CeO₂ interactions.