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

Abstract

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 α-, β- and hierarchically α@β-crystal phases were synthesized. α@β-MnO2 catalysts showed the excellent activity than pure MnO2 in toluene combustion, either α-MnO2 or β-MnO2. The catalytic activity was strongly related with the ratio of α-MnO2 and β-MnO2 in α@β-MnO2 catalyst, and α@β-MnO2 (1:1) exhibited the highest activity for toluene oxidation and toluene can be completely oxidized to CO2 and H2O at about 205 °C with a space velocity (GSHV) of 30,000 h−1. HRTEM, Raman and XPS demonstrated that α@β-MnO2 owned the abundant defects due to the mixed phase interfacial structure. The strong synergistic effect in α@β-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 α-MnO2 and β-MnO2 was 1:1, α@β-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 α@β-MnO2 was beneficial to the improvement of toluene catalytic oxidation activity.