Low-temperature catalytic performance of toluene oxidation over Cu-Mn oxide catalysts derived from LDH precursor

Abstract

A series of CuMn mixed oxides catalysts (CMO-T) were prepared by calcination of CuMn layered double hydroxides (CuMn-LDH) for catalytic oxidation of toluene. The obtained CMO-400 catalyst exhibited a high catalytic activity with T50 and T90 of 210 and 231 °C (WHSV = 30000 mL·g−1·h−1). Meanwhile, the CMO-400 exhibited high stability and durability even at 20 vol% water vapor. The effects of calcination temperature on the texture and structural properties were investigated systematically, which proved the formation of copper-manganese solid solution with abundant multiple-phase interfaces. In addition, the strong interaction between Cu and Mn could lead to more surface adsorbed oxygen due to oxidation reduction cycle of Mn3++Cu2+=Mn4++Cu+. Accordingly, for CMO-500 catalyst, the formation of spinel Cu1.5Mn1.5O4 phase prevented good dispersion of the manganese-oxide phases and weakened the reducibility and oxygen mobility. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) revealed that the intermediates accumulated continuously were difficult to be oxidized rapidly without the replenishment gaseous oxygen. Moreover, the complete transformation of the intermediate benzoate may be the key rate-controlling step in the reaction. The Facile method of preparing mixed-metal solid solution from LDH precursor system could be widely developed for the design of transition metals in catalytic oxidation of toluene.