| With the world-wide importance of environmental protection.When gasoline used as energy, the low content of olefins, aromatics and ethers is higher and higher, this will be reducing gasoline octane number. Isomerize the straight chain alkanes is the most efficient method to increase octane number,which has been acknowledge by many researchs.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.MCM- 41 mesoporous molecular sieves has orderly one-dimensional six-party channel structure,adjustable pore diameter at the range of 1.5-10 nm and high specific surface area et al. Therefore, mesoporous silica MCM-41 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-41 such as low acid strength and bad thermal stability et al. In this paper, the room temperature and hydrothermal crystallization method have synthesized rare earth modified MCM-41 molecular sieve as carrier, 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 in situ doping Ce on the structure, morphology and acidity were studied. The catalytic performance of Ni-HPW/Ce-MCM-41 for n-heptane isomerization was also studied. The main contents were discussed as follows:1 MCM-41 with Ce in situ doping at room temperature and hydrothermal crystallization method have synthesized, the influences of different Ce content and preparation method on molecular sieve structure, morphology, and acid were studied. Experimental results show that,compared with room temperature method, MCM- 41 prepare by hydrothermal crystallization method has well order, with the increase of cerium, the order degree of two preparation methods of Ce- MCM- 41- x has descend, but the influence on MCM- 41 prepared by room temperature method is greater. Ce-MCM-41-x prepared by hydrothermal crystallization method has big crystal cell parameters, pore volume big pore wall thickness, otherwise, the product with hydrothermal crystallization method has small specific surface area. With same Ni and HPW contents, Ce-MCM-41-x as carrier,hydrothermal crystallization method prepared catalyst has stronger acidity.2 The Ni-HPW/Ce-MCM-41 bifunctional catalysts were prepared by step impregnation method, the metal Ni and heteropolyacid HPW were used as active components and rare earth modified MCM-41 was used as support. The influences of preparation conditions, reduction conditions and reaction conditions on catalytic performance of rare earth modified MCM-41 catalysts were studied. The results showed that at the preparation conditions of 3wt%Ni, 20 wt%HPW, 0.03 n(Ce)/n(Si), calcination temperature 400 oC and the reduction conditions of reduction temperature 400 oC, reduction time 4 h and the reaction conditions of reaction temperature 250 oC, reducing hydrogen flow rate 40mL/min, the conversion of catalyst prepared by room temperature and hydrothermal crystallization method have reached 20.5% and 24.3% respectively and the isomerization selectivity have reached 88.7% and 78.1%. |
