Superior performance of alpha@beta-MnO2 for the toluene oxidation: Active interface and oxygen vacancy

The crystalline phase of manganese dioxide catalysts shows strong influence on its catalytic performance, and the construction of hierarchically nanostructured materials with active interface and oxygen vacancy is an effective approach to develop the enhanced functionality. Herein, nanosized MnO2 catalysts with alpha-, beta- and hierarchically alpha@beta-crystal phases were synthesized. alpha@beta-MnO2 catalysts showed the excellent activity than pure MnO, in toluene combustion, either alpha-MnO2 or beta-MnO2. The catalytic activity was strongly related with the ratio of alpha-MnO2 and beta-MnO2 in an-MnO2 catalyst, and alpha@beta-MnO2 (1:1) exhibited the highest activity for toluene oxidation and toluene can be completely oxidized to CO2 and H2O at about 205 degrees C with a space velocity (GSHV) of 30,000h(-1). HRTEM, Raman and XPS demonstrated that alpha@beta-MnO2 owned the abundant defects due to the mixed phase interfacial structure. The strong synergistic effect in alpha@beta-MnO2 catalyst with larger specific area enhanced and facilitated the adsorption and activation of toluene molecules and oxygen species. The mobility of oxygen species and low-temperature reducibility compared with pure MnO2 were significantly enhanced. When the ratio of alpha-MnO2 and beta-MnO2 was 1:1, alpha@beta-MnO2 reached the maximum biphase interface content, formed large amount of oxygen vacancy, and showed the strongest synergistic effect and activation ability for reactants. Thus it was thought that the formation of the special biphase structure of alpha@beta-MnO2 was beneficial to the improvement of toluene catalytic oxidation activity.