| Chlorinated volatile organic compounds (CVOCs) are considered as pollutants hazardous to both ecological environment and human health. With the rapid industrial development, the emissions are much more serious. Therefore, it is urgent to eliminate CVOCs pollution problems. Catalytic oxidation has been identified as one of the most effective techniques for CVOCs elimination due to the advantages of low energy consumption, high removal efficiency and low secondary pollution. Currently, more and more researchers have focused on the relevant catalytic materials.In this paper, CeO2-TiO2 mixed oxides catalysts were prepared by sol-gel method to study the effects of different Ce/Ti molar ratios on the catalytic performance for DCE oxidation. Based on the above results, further investigation of the effect of different preparation methods on the catalytic oxidation of DCE was evaluated. Moreover, the effect of different transition metals doping and doping amount of Fe on the catalytic performance of CeO2-TiO2 catalysts was also investigated. Furthermore, all the catalysts were characterized by N2 adsorption/desorption, XRD, H2-TPR, UV-Raman, HRTEM, XPS, NH3-TPD and TPSR techniques to study the physicochemical properties of the catalysts. Some specific conclusions from this work are drawn as follows:1. A series of CeO2-TiO2 catalysts with different Ce/Ti molar ratios were prepared and investigated. The results indicated that CeO2-TiO2 mixed oxides showed better performance for the catalytic oxidation of DCE compared with pure CeO2 or TiO2. The CeO2-TiO2 mixed oxide with Ce/Ti molar ratio of 1/4 exhibited the highest catalytic activity with trace of chlorinated by-products detected during the decomposition of DCE. The reason may be that the strong interaction between CeO2 and TiO2 promoted the adsorption, improved the mobility of active oxygen species as well as the surface acidity, and thus benefited the deep oxidation activity of DCE as well as the durability of the catalysts.2. The Rietveld's structural analysis revealed that the CeO2-TiO2 mixed oxides were composed of highly dispersed nanocrystallites of CeO2 and TiOx. The Ce-rich samples were composed of c-CeO2, titanium suboxides (Ti2O3 and TiO1.25) and a new h-TiO2 phase. As for the Ti-rich samples, no titanium suboxide phases were detected and little anatase phase with relatively large crystallite size appeared when Ce/Ti ratio reached 0.25. Moreover, the crystallite size of CeO2 in these samples decreased obviously and the lattice microstrain of CeO2 increased regularly with increasing TiO2 content.3. Coprecipitation, sol-gel and deposition methods were chosen to prepare CeO2-TiO2 catalysts on which the catalytic performance of DCE decomposition was investigated. It is found that CeO2-TiO2 mixed oxides prepared by coprecipitation and sol-gel methods had larger specific area, better dispersion of CeO2 and TiOx species and improved redox property which promoted the further deep oxidation of DCE, and thus exhibited better catalytic performance.4. The effect of different transition metals doping on the structural property, redox property and catalytic performance of CeO2-TiO2 catalysts for DCE oxidation was investigated. The results showed that the introduction of Fe, Co, Ni and Mn significantly promoted the catalytic activity of CeO2-TiO2 catalysts for DCE oxidation, especially for the 1Fe9(1Ce4Ti)-SG catalyst. The appropriate amount of Fe doping enhanced the interaction between CeO2 and TiOx, improved dispersion and reduction of the species. However, the introduction of Cu and Cr inhibited the activity of DCE oxidation. Meanwhile, the 1Fe9(1Ce4Ti)-SG catalyst exhibited the best performance for DCE oxidation among the catalysts with various iron contents. |
PDF Full Text Request