| Catalytic oxidation is one of high efficiency, low consumption method for the elimination of chlorinated volatile organic compounds (CVOCs). The core of catalytic oxidation technology is the catalysts. Hence, choosing a suitable catalyst is the key of catalytic oxidation technology. However, the oxidation of CVOCs is very difficult. Currently, some catalysts that have been reported have the disadvantages of higher reaction temperature, easy poisoning and so on. Al-based catalysts are usually used to remove the CVOCs, because Al2O3 has strong acid sites, which are beneficial for adsorbing CVOCs molecular on the surface of the catalyst, and then the catalytic degradation of CVOCs will become easier. However, the catalytic performance of pure alumina is not good enough for CVOCs total oxidation. It is important that study the reaction mechanism of catalyst oxidation of CVOCs over Al-based catalysts for exploring more efficient, economy, environmental friendly catalysts for the elimination CVOCs. In addition, automobile exhaust has become one of the main pollution sources in last several decades, causing many serious environmental problems. Three-way catalysts (TWCs) have been widely used to control gasoline engine exhaust due to its excellent conversion for CO, HC and NOx. Typical TWCs are composed of mainly three parts, including precious metals serving as active components, γ-Al2O3 as a support, and Ce-Zr mixed oxide as promoters. However, the resistance to thermal aging has become one of the main concerns for the catalysts design, because the TWCs serve in the environment with high steam content (up to 10%) and temperature (up to 1050℃) during normal operation in the catalytic converter.The main research contents and results of the thesis are as follows:1. A series of CeO2-promoted Rh1/Al2O3 catalysts were prepared by an incipient wetness impregnation method. These catalysts were tested for catalytic oxidation of CH2Cl2.Various characterization results suggested that the catalytic activities were 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. The reaction mechanism was discussed for CH2Cl2 catalytic oxidation over Rh/xCeO2/Al2O3 catalysts.2. A series of Pd catalysts supported on commercial Ce-Zr solid solution (Pd/CZx) and Al2O3 (Pd/LAx) with support calcined at different temperatures (500,750,900 and 1050℃) were prepared using an incipient wetness impregnation method. The activities of the fresh and hydrothermally aged Pd/CZx catalysts were tested for total oxidation of CO and C3H8. The TOF of CO oxidation on Pd/CZx or Pd/LAx catalysts were closely related to the reducibility of catalysts originated from the existence of different intimate contact between Pd particles and support, and the higher the reducibility, the higher the TOF value. However, the TOF of C3H8 total oxidation on Pd/CZx or Pd/LAx catalysts was main affected by the size of precious metal particle. Large Pd particles are beneficial to C3H8 total oxidation.3. La2O3-modified alumina prepared by three different ways and calcined at different temperatures (500,1000 and 1200℃) were investigated by Physical adsorption, X-ray powder diffraction and Fluorescence spectra. Phase analysis results show that La2O3 can restrain the phase transformation of γ-Al2O3 to α-Al2O3. BET results show that the La2O3-modified alumina possess higher specific surface area and the thermal stability of alumina obviously increases. The specific surface area of La-Al2O3(N) prepared by La(NO3)3 with impregnation method calcined at 1200℃ reaches 30 m2·g-1,which is 2.2 times as large as the La-free alumina calcined at the same temperature. |
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