| CO oxidation is of great practical and academic importance. It is proposed that the support and mental oxide have a major effect on the activitives of catalysts and the synergy effect promotes the activity of catalysts for the CO oxidation. Due to the structure complexity of the catalysts, the specific effects of the catalysts are hardly studied systematically. However, the surface metal oxide could be removed to separate from support by the means of acid treatment and thus simplify the problem. Moreover, with the popularization of lean-burn natural gas vehicles (NGVs), to reduce the emission of CH4becomes more and more important. However, the temperature of off-gas of NGVs is lower than550℃, which disables the traditional catalysts for CH4combustion. Hence, it is necessary to research and develop a new-style catalyst with higher activity under the low temperature. The main contents of the thesis are as follows:1. A series of xMOy/Ce0.9M0.1-xO2-δ (M=Cu, Ni, Co, Fe) catalysts (Ce-M) were prepared by a sol-gel method and corresponding Ce0.9M0.1-xO2-δ catalysts (HCe-M) were obtained with an acid treatment. It was found that the Ce-M catalysts contained surface MOy species and Ce0.9M0.1-xO2-δ solid solution, as confirmed by the results of X-ray diffraction and Raman spectra, respectively. While the HCe-M catalysts only contained Ce0.9M0.1-xO2-δ solid solution. CO oxidation over these catalysts revealed that the activities followed an order of Ce-Cu> Ce-Ni> Ce-Co> Ce-Fe, but were remarkably higher than the corresponding HCe-M samples. The activities of the HCe-M catalysts were closely related to their reducibility originated from the oxygen vacancies in these samples. The most active HCe-Cu catalyst had the highest content of oxygen vacancies and thus was the most reducible. For the Ce-M catalysts, the enhanced catalytic performance was due to a synergy between the surface MOy species and the Ce-M-O solid solution, as the former provided sites for CO chemisorption and the latter promoted the activation of oxygen.2. Aiming at comparing the CO oxidation activity of free PdO and Pd2+ions, a series of PdO-CeO2/SiO2catalysts were prepared via an impregnation method and the turnover frequencies of them were quantitatively evaluated. The catalysts were further characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), temperature-programmed reduction (TPR), Raman technique and CO chemisorption. It was found that free PdO species and Pd2+ions could be segregated efficiently by nitric acid treatment. The PdO-CeO2/SiO2catalyst calcined at600℃showed the highest activity. The results of CO chemisorption suggested that free PdO species had a higher activity than Pd2+ions, and the turnover frequencies of them were3.27×10-2s-l and0.49×10-2s-1, respectively. The activity of PdO-CeO2/SiO2catalyst was higher than that of Pd0/SiO2catalyst. Moreover, the CO catalytic activity of PdO-CeO2/SiO2catalyst could be assigned to the synergetic effect of free PdO and Pd2+ions, and this effect could improve the CO catalytic activity of catalysts.3. Mesoporous Pd/Co3O4catalyst was prepared using2D porous SBA-15and3D porous KIT-6as the hard template and CoCr2O4catalyst was prepared by a sol-gel method. The catalysts were used for CH4combustion and the results showed that Pd/Co3O4-3D and CoCr2O4catalysts had a similar activity. However, the spinel CoCr2O4catalysts had application prospect and value from a certain perspective of application. Moreover, the catalysts with Cu, Ni, Mn, Sn cations doped in the catalyst hardly improve the activities of the catalysts. |
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