Research On The Preparation And Catalytic Performance Of Rare Earth Modified MCM-48 Bifuctional Catalyst

Gasoline is one of indispensable energy to modern society.With the world-wide importance of environmental protection,new environmental regulations imposed the reduction of content of olefins,aromatics and ethers,which may lead to a loss in the octane number.So it was an important means that isomerize the straight chain alkanes to increase octane number.The catalysts of long chain alkane isomerization were mainly porous zeolite supported bifunctional catalysts in recent years.That type of catalysts went against the conversion from long chain alkanes to multibranched isoalkanes because of high cracking rate and small pore channel.Therefore,the researchers were keen on researching the catalysts with high specific surface area,high porosity,good thermal stability and high catalytic activity.There were many advantages of mesoporous silica MCM-48 such as three-dimensional interwoven channel structure,adjustable pore diameter at the range of 2～10nm and high specific surface area et al.Therefore,mesoporous silica MCM-48 was used as support,which was beneficial to material transmission and the dispersion of active components.However,there were some disadvantages of mesoporous silica MCM-48 such as low acid strength and bad thermal stability et al.In this paper,rare earth modified MCM-48 was used as support and nickel-heteropolyacid supported bifunctional catalysts were prepared.By means of XRD,N2 adsorption-desorption,FT-IR,SEM,NH3-TPD,and TG/DTA techniques,the influences of Ce on the structure,morphology,acidity and stability were studied.The catalytic performance of Ni-HPW/Ce-MCM-48 for n-heptane isomerization was also studied.The main contents of this paper were discussed as follows:1.Rare earth modified mesoporous silica MCM-48 was prepared by in-situ doping hydrothermal synthesis.The influences of different preparation conditions on the structure of mesoporous silica MCM-48 were discussed.The results showed that mesoporous silica MCM-48 with better long-range order was prepared at the conditions of 0.03 Ce/Si,crystallization temperature 120℃,crystallization time 72 h,calcination temperature 550℃and calcination time 4 h.2.The Ni-HPW/Ce-MCM-48 bifunctional catalysts were prepared by step impregnation method,the metal Ni and heteropolyacid HPW were used as active components and rare earth modified MCM-48 was used as support.The influences of preparation conditions,reduction conditions and reaction conditions on catalytic performance of rare earth modified MCM-48 catalysts were studied.The results showed that the conversion and the selectivity reached 41.9%and 85.8%respectively at the preparation conditions of 4 wt%Ni,20 wt%HPW,0.03 Ce/Si,calcination temperature 400℃ and calcination time 4 h and the reduction conditions of reduction temperature 400℃,reduction time 4 h and the reaction conditions of reaction temperature 280℃,WHSV 6.8 h-1 and 8 H2/n-C7).