Promotion mechanism of CuMn2O4 modification with NaOH on toluene oxidation: Boosting the ring-opening of benzoate

Abstract

To elucidate the mechanism of the promotion effect of CuMn2O4 catalyst modification with NaOH on toluene oxidation, NaOH-modified CuMn2O4 catalysts with similar physical structures and chemical properties were fabricated through a mild impregnation strategy. The results showed that the NaOH species had a remarkable promotion effect on the CuMn2O4 catalytic performance without lattice oxygen activity improvement. The 2NaOH/CuMn2O4 showed the best catalytic activity with the T90 (the temperature corresponding to 90% conversion) of 188 °C, which was 20 °C lower than that of the unmodified CuMn2O4. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFT)S study revealed that carbonate and benzoate were the main intermediates over CuMn2O4, and the NaOH introduction inhibited carbonate formation and accelerated the degradation of the benzoate aromatic ring. The H2O present in the reaction system could be dissociated into hydroxyl groups under the action of NaOH to form a hydroxyl-rich environment, which boosted the ring-opening of benzoate. In addition, the toluene adsorption experiments confirmed that the nucleophilic lattice oxygen species broke the activated aromatic ring, and the toluene oxidation followed the Mars–vanKrevelen mechanism. In this study, the mechanism of the promotion effect of catalyst modification with NaOH on toluene oxidation was revealed, which is of great significance for the design of high-efficiency toluene degradation catalysts.