The Catalytic Performance Of ZrO₂Doped CeO₂-CrO_x Atalysts For CVOCs Oxidation

With the rapid development of science and technology and the expansion of human activities, awareness concerning natural environment is seriously necessary for sustainability. As one of the major sources of atmospheric pollutants, chlorinated volatile organic compounds (CVOCs) not only have serious effects on the environment, but also damage human body a lot. Therfore, in order to ensure cleaner breathable air for future generations, it has called for strict measures and environmental regulations to be put in place. Among various methods of chlorocarbons disposal, catalytic oxidation degradation has been deemed to be the most effective way to destruct CVOCs, due to its highly efficient, low energy consumption and no secondary pollution. Recently, the development of catalysts with low cost, high activity, high selectivity and good stability for CVOCs catalytic oxidation has been one of the most important topics in environmental catalytic material research field.In this paper, CeO2-ZrO2-CrOx mixed oxides were prepared by coprecipitation method to research the influences of different Ce/Zr molar ratios on the catalytic performance for DCE degradation. Based on the above results, the effects of different acidic materials (HZSM5, TiO2, Al2O3and SiO2) on the catalytic performance for DCE destruction were further evaluated. Moreover, in order to be more suitable for industrial application, the influence of the presence of H2O or C6H6on DCE degradation performance was also further studied. At last, the mechanisms of catalytic degradation of DCE, DCM, TCE and CB over CZCr/HZSM5catalysts were studied preliminarily. The texture-structures, redox properties and surface acidity distributions of these catalysts were characterized by XRD, N2adsorption/desorption, XPS, UV-Raman, SEM, H2-TPR and NH3-TPD techniques. Some specific conclusions from this work are listed as follows:1. Catalytic performances for DCE degradation over CeO2-ZrO2-CrOx catalysts with different Ce/Zr molar ratios were evaluated. The results show that proper amount of ZrO2is conducive to improve the catalytic performance compared with the pure CeO2-CrOx catalyst. Especially, the CZCrll catalyst (Ce/Zr molar ratio was1:1) shows the best catalytic activity and thermal stability. Moreover, CZCrll catalyst represents high selectivity to HC1, and only small amounts of chlorinated by-products were detected. It can be speculated that appropriate ZrO2doping increased the structural stability, mobility of active oxygen species and redox property, which are favorable for promoting the adsorption, activation and deep oxidation of DCE.2. Catalytic performances for DCE degradation over CeO2-ZrO2-CrOx catalysts with different acidic materials (HZSM5, TiO2, Al2O3and SiO2) were evaluated. The results show that rich acidic sites and good redox property are both conducive to improve the ablity of adsorption and activation of the reactant molecules. The catalytic performances of20%-CZCr/HZSM5catalyst for various CVOCs oxidation are significantly promoted compared to that of CeO2-ZrO2-CrOx or HZSM5, and the existence of CeO2-ZrO2-CrOx can significantly improve the redox property and adjust the strong/weak acid density distribution of the HZSM5, resulting in20%-CZCr/HZSM5catalyst represents the best catalytic activity and thermal stability for DCE degradation. The catalytic activity for the oxidation of different CVOCs over20%-CZCr/HZSM5catalyst is displayed as follows:DCE>DCM>CB>TCE.3. Influence of the presence of H2O or C6H6on DCE degradation performance were also further studied. The results show that the catalytic activity for DCE elimination is obviously decreased in the presence of H2O or C6H6, which may be related to the competitive adsorption of H2O or C6H6with DCE on active sites. Especially, C6H6shows stonger competitive adsorption on active sites, resulting in the depth of oxidation ability declined and easier to form carbon deposition.4. Catalysts used for the Cl-VOCs oxidation reaction may suffer from passivation, and coke formation is one of the mian reasons. CeO2-ZrO2-CrOx catalyst represents good durability for DCE degradation, and the addition of CeO2-ZrO2-CrOx significantly improves the durability of HZSM5because of its strong oxidizing ability.