Activation of Oxygen on the Surface of the Co3O4 Catalyst by Single-Atom Ag toward Efficient Catalytic Benzene Combustion

Supported noble metal-based catalysts have been extensively studied for catalytic benzene combustion during the past decade because of their high activity. Despite the enormous significance of noble metal-based materials as benzene combustion catalysts, the key properties of catalytic active sites and the plausible benzene combustion mechanism are a matter of debate. Herein, a well-defined model catalyst consisting of single Ag atoms deposited on Co3O4 oxide surfaces has been prepared and used to provide mechanistic insights into the benzene combustion mechanism and the origins of the excellent reactivity of Ag. The single-atom Ag-on-Co3O4 catalyst exhibits excellent activity and stability for benzene combustion. T100 (temperature required to reach 100% conversion of benzene) is achieved at 204 °C. Scanning transmission electron microscopy reveals that single Ag atoms on Co3O4 are anchored to Co3+ vacancy sites on the support surface. Single-atom Ag incorporates excess oxygen and activates abundant Ag–O–Co bonds for reaction with benzene, thereby enhancing catalytic activity. The plausible benzene combustion path over the single-atom Ag-on-Co3O4 catalyst is proposed to be benzene → phenolate → quinone → maleate → acetate → CO2 + H2O. The rate-limiting step is located in the maleate → acetate → CO2 + H2O cycle at a temperature of 200 °C. The feasibility of this reaction pathway was confirmed from diffuse reflectance infrared Fourier transform spectroscopy experiments. We anticipate that these observations will improve our understanding of surface chemical processes in heterogeneous catalysis and provide useful information for the rational design of high-performance catalysts for benzene combustion reactions.