Promoting the Generation of Active Oxygen over Ag-Modified Nanoflower-like α-MnO<sub>2</sub> for Soot Oxidation: Experimental and DFT Studies
Yuhang Wang, Longzhu Zhang, Changsen Zhang, Xingmin Xu, Yunyun Xie, Wenjun Chen, Jie Wang, Ruiqin Zhang
Abstract
The hydrothermal method was used to synthesize α-MnO2 with nanoflower-like (NF) and nanowire-like (NW) morphologies. Besides, different amounts (5–15 wt %) of silver were loaded into flowerlike α-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 α-MnO2 result in different Oxn– generating capacities, as shown in the X-ray photoelectron spectroscopy (XPS) test. The NF had the highest ratio of highly reactive superoxide (O2–). In addition, the NF modified by optimal amounts of Ag could speed up the O2– generation caused by the largest amount of surface oxygen vacancies. The density functional theory calculation revealed that the oxygen vacancies on α-MnO2 species could improve the adsorption of reactants and increase the surface energy of the as-prepared catalyst, which result in excellent catalytic performance of Ag(10)-NF.