Amorphous-microcrystal combined manganese oxides for efficiently catalytic combustion of VOCs

Catalytic combustion is an efficient technology for the volatile organic compounds (VOCs) elimination. The effect of crystalline integrity on catalytic combustion activity over MnOx has been investigated, and the amorphous MnOx with partial crystallization (Crystallinity = 6 %) shown higher activity than pure amorphous and intact crystal MnOx (Crystallinity = 1 % and 100 %, respectively). Firstly, amorphous MnOx has been prepared by glucose reduction method and the crystalline integrity has been adjusted by tuning the hydrothermal temperature and time. Besides, the various characterizations illustrated that the appropriate crystalline integrity can result in enhancing catalytic combustion reactivity due to the synergistic impact of amorphous and crystalline phase. The amorphous phase has abundant structure defects and unsaturated coordination bonds, which enhances adsorption ability of catalyst. Simultaneously, the crystalline phase drives electrons migration, which favors the adsorption and activation of oxygen and speeds up the redox reaction rate. The synergy between amorphous and crystal phase gives catalyst the most of dominant adsorbed oxygen species, Mn4+ species and the strongest oxygen supply capacity. Furthermore, mesoporous structures were formed in the early stage of crystallization of amorphous MnOx which gave the manganese oxides the largest specific surface area (192 m(2)/g). This work shows a novel strategy to design and prepare efficient non-precious metal catalysts for VOCs catalytic combustion.