Study Of Catalytic Combustion Of CVOCs Over Aluminium-Based Catalysts

Catalytic oxidation is an efficient and low consumption technology to remove chlorinated volatile organic compounds (CVOCs), which has advantages of simple equipment, good safety performance, and so on. Thus it is a promising technology on oxidation of CVOCs. The core of CVOCs catalytic oxidation technology is catalyst systems. The currently reported catalysts for oxidation of CVOCs have shortcomings such as high reaction temperature, easy poisoning, short life and so on. Al-based catalysts have been widely applied in abatement of chlorinated volatile organic compounds because of its surface acidity, which helps to adsorb chlorinated volatile organic compounds on the catalyst surface and thus makes degradation of CVOCs easier. However, pure alumina is not active for this reaction; development of highly efficient catalysts to meet the industrial application is the target of this work. Research contents and results of this thesis are as follows:1. Al2O3support was prepared by a precipitation method, and then a series of Pt/Al2O3catalysts were prepared using a impregnation method and tested for catalytic oxidation of CH2Cl2. The activity test results indicated that these catalysts were highly active in the oxidation of CH2Cl2, with a complete oxidation temperature of420℃. XRD and CO adsorption results showed that the Pt species were highly dispersed on the catalysts surface, and the crystallite sizes of Pt species were very small. H2-TPR results indicated that the redox performance of catalysts was significantly improved after impregnating Pt species, which may be the reason of the enhanced activity.2. A series of CeO2-Al2O3catalysts with different CeO2contents were prepared by a co-precipitation method, and supported Pt/CeO2-Al2O3catalysts were also prepared by an impregnation method. These catalysts were tested for catalytic oxidation of dichloromethane (CH2Cl2). It was found that these catalysts were active for the reaction, with a100%conversion of CH2Cl2obtained at410℃over a catalyst with15%of CeO2. Various characterization results such as ammonia temperature programmed desorption, hydrogen temperature programmed reduction suggested that the catalytic behaviors were synergisti-cally influenced by surface acidity and redox property of the catalysts. An optimal combination of surface acidity and redox property in the catalyst resulted in a high activity. Moreover, the addition of Pt could further enhance the activity, due to the promotion of surface acidity by the introduction of chlorine species in the catalyst during the preparation using H2PtCl6as the precursor and reducibility of the catalyst probably via the formation of Ce-Pt-O solid solution.3. Cr2O3-CeO2-Al2O3catalysts with different Cr contents were synthesized using Cr(NO3)3-9H2O, Al(NO3)3·9H2O and Ce(NO3)3·6H2O as the precursors by an co-precipitation method, and Pt/Cr2O3-CeO2-Al2O3catalysts with different Pt loadings were prepared using H2PtCl6·6H2O as the precursor by an impregnation method. These catalysts were tested for catalytic oxidation of CH2Cl2and their thermal stabilities were also investigated. The results indicated that the Pt/Cr2O3-CeO2-Al2O3catalysts showed high oxidation performance. H2-TPR and NH3-TPD results indicated that the redox property and surface acidity has been much improved after adding chromium oxide. This may be the main reason to interpret high activity of the2.0Pt/Cr2O3-CeO2-Al2O3catalyst. Moreover, the catalysts showed high thermal stability during the reaction.