| It is accepted that more attention was paid on environmental protection all over the world. As a promising method to increase octane number of gasoline, the isomerization of n-heptane has attracted extensive attention. A series of rare earth modified solid acid catalysts were prepared by selecting supports with different structure. The influences of rare earth on the structure, morphology, acidity, stability and performance of catalyst were investigated. By controlling po re structure, acidity, dispersion of metal active component of the supports, the relationship between isomerization activity, acidity, metallic, and shape selectivity of zeolite were determined.Ni-Re/SAPO-11(Re: Ce, Pr, La, Y, Nd) were prepared by step impregnation method. The influencing factors on the isomerization of n-heptane, such as Ni content, types of rare earths, reaction temperature, reduction temperature, space velocity(WHSV) and hydrogen flow rate, were studied by orthogonal test. The results show that the main influencing factor of n-heptane conversion and selectivity of products was the reaction temperature. The isomerization selectivity was mainly affected by Ni content, and the types of rare-earth metal has little influence on n-heptane reactivity. The influences of Ce on the structure and catalytic performance of 4mass%Ni/SAPO-11 were studied on the basis of orthogonal test. Compared with Ni/SAPO-11, the specific surface area, pore volume and the dispersion of Ni were improved by the introduction of Ce. The results of FT-IR show that there is a small amount of Ce3+ ions emerged in the framework of molecular sieve during the impregnation process.A series sample of rare earth elements modified mesoporous MCM-48 were prepared by hydrothermal method. The influences of preparation parameters on the structure of mesoporous MCM-48 were discussed. The results show that mesoporous MCM-48 with dodecahedron crystal morphology was obtained at the conditions of molar ration of 0.02 for Ce/Si, crystallization temperature of 110 oC, crystallization time of 72 h, calcination temperature of 550 oC with the time of 4 h. Compared with MCM-48, the pore size, pore wall of Ce-MCM-48 were improved. Moreover, the hydrothermal stability was enhanced by the increasement of new Br?nsted and Lewis acid site with introducing Ce ions into the framework of MCM-48.Bifunctional catalysts for n-heptane isomerization were prepared by using MCM-48 and Ce-MCM-48 as support, and taking heteropoly HPMo with Keggin structure and Ni as activity components by step impregnation method. Compared with MCM-48, Ce-MCM-48 is more suitable than HPMo as a carrier. After calcination, HPMo still kept the Keggin structure, and the Ce-MCM-48 loaded with HPMo has greatly enhanced the acid amount and acid strength.The catalytic performance of different Ni supported solid acid catalyst was studied. The result reveals that the content of Ni and the acidity of carrier affect the conversion and selectivity of the catalyst. The distribution of isomerization products is mainly related to the pore structure. The ratio of metal site and acid site can be regulated by introducing appropriate rare earth Ce and heteropolyacid into the catalyst, which results in the improvement of the conversion and selectivity. The conversion of n-heptane were 28.8% and the isoheptane selectivity were 82.7% over 4mass%Ni-2mass%Ce/SAPO-11 catalyst. Using 4mass%Ni/Ce-MCM-48 catalyst, the conversion of n-heptane and the isoheptane selectivity were 17.5% and 57.2%, respectively. Moreover, the conversion of n-heptane and the isoheptane selectivity were 22.7% and 75.5% using 4mass%Ni-20mass%HPMo/Ce-MCM-48 catalyst, respectively. SAPO-11 support with one-dimensional pore structure is propitious to the formation of the single branched isomers, and more branched chain isomerism products can be obtained with mesoporous Ce-MCM-48 as support. |
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