Synthesis Of Bimetallic Supported Ce-MCM-48 Catalyst And Its Performance For Heptane Isomerization

As people pay more and more attention to energy and environmental issues,many scholars have begun to research and develop clean gasoline with low aromatics,low sulfur and high octane number.Linear paraffins(C₅～C₁₂)are an important part of gasoline fractions.In order to improve gasoline quality,n-paraffin isomerization has been generally regarded as a benign way of green environmental protection.The preparation of highly active alkane isomerization catalysts is of great significance for practical applications.MCM-48 has unique three-dimensional cubic structure pores,large specific surface area,and good long-range order.Pure silicon MCM-48 mesoporous molecular sieve has fewer active centers,lower ion exchange capacity,and poor hydrothermal stability.In this paper,Ce-MCM-48 is synthesized by in-situ doping method,and the effect of different preparation conditions on the structure of Ce-MCM-48 is studied.The results show that the Ce-MCM-48supports prepared under the conditions of crystallization temperature of 110 ^oC,crystallization time of 72 h,calcination temperature of 550 ^oC,calcination time of 4 h and Ce/Si molar ratio of 0.02 are of good quality.Co/Ce-MCM-48 and Cr/Ce-MCM-48 samples are prepared by impregnation method with Ce-MCM-48 as carrier.Ni-Co/Ce-MCM-48 and Ni-Cr/Ce-MCM-48 catalysts are prepared by co-impregnation with nickel nitrate,cobalt nitrate and chromium nitrate as the metal sources,respectively,with Ce-MCM-48 as the support.The structure and performance of the two catalysts are analyzed by XRD,FT-IR,SEM,TEM,N₂adsorption-desorption,NH₃-TPD and other characterizations.The catalytic performance of Ni-Cr/Ce-MCM-48 and Ni-Co/Ce-MCM-48 bifunctional catalysts were investigated by n-heptane isomerization reaction.Experiments show that the best preparation conditions of the two catalysts are as follows:calcination temperature is 400^oC,calcination time is 4 h,nickel loading is 1.5%,Ce/Si molar ratio is 0.02,and cobalt and chromium loadings are both 1%.The best reduction temperature is 400 ^oC,and the best reduction time is 4 h.The optimal reaction conditions are as follows:the weight hourly space velocity is 6.8 h^-1,the hydrogen-oil ratio is 8,and the reaction temperature is 280 ^oC.The conversion and selectivity of 1.5%Ni-1%Co/Ce-MCM-48-0.02 catalyst are 51.6%and 64.5%,respectively.The conversion and selectivity of 1.5%Ni-1%Cr/Ce-MCM-48-0.02 are 60.8%and 72.3%,respectively.By comparison,the catalytic performance of1.5%Ni-1%Cr/Ce-MCM-48-0.02 for alkane isomerization is better than the other one.