High-efficiency HCHO oxidation over dumbbell-shaped Ag/α-MnO2 hollow microshperes with low Ag loading

Dumbbell-shaped α-MnO 2 hollow microspheres were synthesized via surface chemical oxidation of MnCO 3 microspheres using KMnO 4 , followed by removal of the residual MnCO 3 template with HCl. Subsequently, a series of Ag-modified α-MnO 2 catalysts with nominal loadings of m % Ag ( m  = 0.05, 0.1, 0.3 and 0.5) were prepared through a redox etching process using H 2 O 2 . The strong interaction between highly dispersed Ag and the α-MnO 2 support was found to enhance the low-temperature reducibility and generate abundant active oxygen species. Furthermore, the presence of Ag increased the concentrations of Mn 2+ and Mn 3+ species, thereby facilitating the formation of oxygen vacancies. Simultaneously, the dynamic redox cycles between Ag + /Ag and Mn 4+ /Mn 3+ significantly improved oxygen mobility within the catalyst. These synergistic effects collectively contributed to the outstanding catalytic performance of the 0.3% Ag/α-MnO 2 , which achieved 75.8% HCHO conversion at 30 °C and reached complete conversion at 50 °C. In situ DRIFTS studies revealed that the addition of Ag into α-MnO 2 promoted the carbonate species qulickly converted into CO 2 and H 2 O. Both α-MnO 2 and 0.3% Ag/α-MnO 2 catalyst followed a similar reaction pathway of HCHO → DOM → HCOOH → H 2 CO 3  → CO 2  + H 2 O.