Metallic Ag⁰-induced electron transfer at Ag-CeO₂ Interface: The key to efficient CO oxidation

Interfacial Ag° content of Ag-CeO 2 catalysts was modulated by pyrolysis temperature. • Rich Ag 0 catalysts had higher catalytic ability than those rich in Ce 3+ and defects. • Temperature triggered electron transfer of Ag 0 to carbonate-activated CeO 2 interface. • Dynamic evolution of Ag-CeO 2 interface determined catalytic capacity of its catalyst. Ag-CeO 2 catalysts were fabricated with an agar-assisted pyrolysis method and their interfacial structures were tuned to investigate their role in CO oxidation. The catalysts mainly consisted of irregular CeO 2 nanoparticles with abundant metallic Ag 0 , Ce 3+ and oxygen vacancies at the interface. As the pyrolysis temperature increased, the metallic Ag⁰ content decreased while Ag⁺ and Ce³⁺ species increased. Using CO oxidation as a probe reaction, catalytic evaluation confirmed that the activity was positively correlated with the interfacial metallic Ag⁰ content, whereas no direct positive correlation was observed with Ag⁺, Ce³⁺, or oxygen vacancies alone-suggesting a dominant role of Ag⁰, although a possible synergistic contribution from Ce³⁺/oxygen vacancies is not ruled out. Ag-CeO 2 catalysts after CO adsorption were monitored by XPS and in situ FT-IR for identifying the dynamic evolution of Ag-CeO 2 interface. The reaction temperature was revealed to trigger electron transfer from metallic Ag⁰ to the carbonate-bound CeO₂ interface, which simultaneously converted initially formed polydentate and bidentate carbonates into bridging and monodentate intermediates. The reversible redox transformation (Ag⁰ + Ce⁴⁺ ⇌ Ag⁺ + Ce³⁺) at the interface of these catalysts further corroborated the essential role of Ag⁰ in enhancing the catalytic activities for CO oxidation. These findings, obtained with CO oxidation as a model reaction, differ from the simple traditional correlations with oxygen vacancies or Ce³⁺ concentration, offering a molecular-level blueprint for designing highly active and stable CeO₂-supported catalysts for catalytic oxidation reactions. Download: Download high-res image (440KB) Download: Download full-size image