Studies On Preparation And Catalytic Performances Of Ni-Pt Bimetallic Catalysts

Carbon dioxide reforming of methane to syngas is a research focus in natural gas utilization field. Compared with traditional steam reforming of methane, it can receive lower ratio of H2/CO to be suitable for subsequence processes such as Fischer-Tropsch synthesis etc. Besides, it is an effective way to reduce emission of greenhouse gas and mitigate the energy crisis because of the using of two main greenhouse gases. CH4-CO2 reforming is a catalytic process. Ni-based catalyst has been studied widely as its high catalytic activity, however, loss of active component and carbon deposition on catalyst surfacc lead to the deactivation of conventional Ni-based catalyst.This thesis focuses on investigating the physico-chemical properties of the supported Ni-Pt bimetallic catalysts prepared with different conditions, and evaluating the catalytic performance for CH4-CO2 reforming reaction. Pt was added to the Ni catalyst to improve the dispersion of active component on catalyst surface, therefore, increasing the stability and resistance to carbon deposition of Ni catalyst. The Ce-Zr solid solution having especial storage/release capacity of oxygen was chosen as the support of catalyst, which can enhance interaction between support and active component, promote the ability of transfer oxygen during catalytic reaction, to achieve the objective to restrain the formation of carbon deposition.The physico-chemical properties of Ce-Zr solid solution prepared with co-precipitation method were investigated using lots of techniques, and the optimal condition to prepare solid solution was obtained as follows:co-precipitation method, Ce/Zr=7:3, NH3·H2O as the precipitator, using feeding manner in reverse, the calcined temperature 773K. Results of TEM,XRD and H2-TPR reveals that Ce-Zr solid solution particles which is prepared at this condition have complete crystal, more uniform distribution and higher reducible ability.The 5Ni-xPt catalysts whose support is Ce0.7Zr0.3O2 were prepared by co-impregnation method, and their properties and catalytic performance were characterized. The results show that the catalyst had higher catalytic activity and stability when x=0.75. According to results of H2-TPR and H2-TPD, the catalyst exhibited higher reducible ability because of impoved metal-support interaction, and had more surface active centers. The synergism of Ni-Pt improved the distribution of Ni on the support, the active components of bimetallic catalyst showed better dispersion and resistance to carbon deposition than mono metallic catalyst. The results of CH4-CO2 reforming reaction on 5Ni-0.75Pt catalysts loaned on different supports indicated that the catalyst supported on Ce0.7Zr0.3O2 solid solution had higher CH4,CO2 conversion and ratio of H2/CO. To investigate the effect of active component impregnation sequence on catalytic performance,5Ni-0.75Pt/Ge0.7 Zr0.3O2 catalysts were prepared by sep-impregnation method. The results show that Ni(F)-Pt catalyst exhibited better resistance to carbon deposition, because Pt particles were dispersed on the surface of support uniformly, co-operation of Ni and Pt restrained the formation of carbon deposition on catalyst surface.The deactivation behavior of catalysts was studied. The result indicates that the main reason for deactivation of Ni-Pt bimetallic catalyst was carbon deposition. It's found that the catalyst deactivated quickly when the deposited carbon existed in cage-like structure because of the carbon deposition wrapping the catalyst and blocking the gas channels. However, when carbon had beard shape, it had no influence on the catalytic activity of the catalysts.