Promoting the Generation of Active Oxygen over Ag-Modified Nanoflower-like α-MnO2 for Soot Oxidation: Experimental and DFT Studies

The hydrothermal method was used to synthesize alpha-MnO2 with nanoflower-like (NF) and nanowire-like (NW) morphologies. Besides, different amounts (5-15 wt %) of silver were loaded into flowerlike alpha-MnO2 (Ag(x)-NF) to promote the soot oxidation performance. The resulting catalysts have been characterized by different techniques. Soot oxidation was detected over temperature-programmed experiments. Unequal surface oxygen vacancies in different alpha-MnO2 result in different O-x(n-) generating capacities, as shown in the X-ray photoelectron spectroscopy (XPS) test. The NF had the highest ratio of highly reactive superoxide (O-2). In addition, the NF modified by optimal amounts of Ag could speed up the O-2(-) generation caused by the largest amount of surface oxygen vacancies. The density functional theory calculation revealed that the oxygen vacancies on alpha-MnO2 species could improve the adsorption of reactants and increase the surface energy of the asprepared catalyst, which result in excellent catalytic performance of Ag(10)-NF.