Selective Oxidation of Diethylamine on CuO/ZSM-5 Catalysts: The Role of Cooperative Catalysis of CuO and Surface Acid Sites

Abstract

Achieving the selective oxidation of hazardous nitrogen-containing volatile organic compounds to the harmless molecular N2 still remains a big challenge. Here, we present the synthesis of CuO catalysts supported by ZSM-5 with different SiO2/Al2O3 ratios through the impregnation method. With the X-ray diffraction, hydrogen temperature-programmed reduction, temperature-programmed desorption of NH3, and X-ray photoelectron spectroscopy characterization of the catalysts, the influences of both the SiO2/Al2O3 ratio in ZSM-5 and the amount of CuO loadings on the catalytic oxidation activity and N2 selectivity over CuO/ZSM-5 catalysts for diethylamine oxidation were investigated in detail. As the SiO2/Al2O3 ratio of ZSM-5 decreases from 360 to 18, the catalytic oxidation activity of diethylamine over the CuO/ZSM-5 catalyst increases (T98 decreases), and the selectivity of N2 generation obviously increases. Among them, the 6CuO/ZSM-5-18 catalyst shows the best catalytic performance, of which T98 for diethylamine oxidation is 240 °C, and the selectivity for N2 is exceeding 95.5% at 400 °C. Moreover, the 6CuO/ZSM-5-18 catalyst gives the widest temperature window (ΔT = 160 °C) for N2 selectivity over 95%. The surface acidity of the CuO/ZSM-5 catalyst increases when the SiO2/Al2O3 ratio in ZSM-5 decreases, so that the amount of easily reducible CuO species increases. The CuO species improve the catalytic oxidation activity, and the increasing amount of surface acid sites and strong acid sites on the support are favorable for the activation of diethylamine and the formation of N2. Thus, it could be inferred that the cooperative catalysis of highly dispersed CuO with surface acid sites in the catalyst is beneficial to the selective catalytic oxidation of diethylamine.

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