Selective catalytic oxidation of nitrogen containing volatile organic compounds (NVOCs) is very meaningful but still remains big challenge because it is very difficult to balance the oxidation activity and N 2 selectivity of available catalysts. In order to develop excellent catalysts with high N 2 selectivity in wide temperature window ( △T ) during NVOCs oxidation, CeO 2 modified CuO/ZSM-5 catalysts with different CeO 2 addition order were prepared for diethylamine (DEA) oxidation. Detailed characterizations of catalysts such as XRD, XPS, H 2 -TPR and NH 3 -TPD were conducted, it is found that addition of CeO 2 obviously changes the geometrical and electronic states of CuO active sites in the catalyst, and CeO 2 addition order affects the Ce 3+ ratio on the catalyst surface. Promotion of CeO 2 species enables the generation of more highly active Cu species (Cu + species and finely dispersed CuO clusters) for DEA oxidation; and synergistic catalysis of the Ce 3+ species, active Cu species and acid sites in ZSM-5 leads to the high N 2 selectivity in wide temperature window ( △T ). Compared to the CeO 2 /CuO/ZSM-5 and CuO-CeO 2 /ZSM-5 catalysts, the CuO/CeO 2 /ZSM-5 catalyst exhibits moderate high oxidation activity with T 99 of 230 °C and the widest △T of 150 °C for high N 2 selectivity. Our primary results in this work provide the efficient strategy for improving catalyst employed for NVOCs selective oxidation.
A series of CuO/ZSM-5 catalysts with different copper loadings were prepared by impregnation (IM) and chemical vapor deposition (CVD) methods, respectively. Their physicochemical properties were investigated by N 2 adsorption/desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS), temperature-programmed reduction by hydrogen (H 2 -TPR) and temperature-programmed desorption of NH 3 (NH 3 -TPD). The XRD and TEM results demonstrated that the crystallite size of the CuO prepared by CVD method was smaller than that by IM, and the XPS results illustrated that the copper specie was mostly in Cu 2+ state and Cu + co-existed. The performance of catalytic oxidation of ethyl acetate was conducted in the fixed-bed reactor based on CuO/ZSM-5 catalysts. The experimental results showed that the preparation method affected the catalytic activity of CuO/ZSM-5; the CVD catalysts exhibited a higher catalytic activity for ethyl acetate oxidation compared with the IM catalysts at the same copper loadings. Ethanol and acetaldehyde are observed to be the intermediate products in the combustion of ethyl acetate over the synthesized catalysts. The relative amounts of acetaldehyde and ethanol are determined by the selectivity of the catalyst toward acetaldehyde production from ethanol. Particularly, the 3 wt% CVD catalyst showed the best catalytic activity for ethyl acetate oxidation with 90% conversion of ethyl acetate at 235 °C, which was much lower than that of the 3 wt% IM catalyst (278 °C), meanwhile, the intermediate products of the 3 wt% CVD for ethyl acetate oxidation were completely oxidized into CO 2 and H 2 O at temperature as low as 288 °C.
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