Preparation Of Zirconium Modified MCM-48 And Study On Its Heptane Isomerization Property

The pore structure of MCM-48 mesoporous molecular sieve is three dimensional spiral arrangement,large specific surface area,stable framework structure,however,the shortcomings of pure silicon MCM-48 such as low acid strength,poor ion exchange capacity,weak thermal stability and the lack of necessary active centers have limited its application in the field of catalysis.Therefore,it has an important theoretical and practical significance for developing high-strength mesoporous molecular sieves with high acid strength,good stability and good catalytic activity.In this paper,zirconium modified mesoporous silica MCM-48 was prepared by in-situ doping hydrothermal synthesis.H-Zr-MCM-48 was prepared by modification with ammonium nitrate solution,and Ni/H-Zr-MCM-48 catalyst was prepared with incipient impregnation method.The results of XRD,N2 adsorption desorption,SEM,TEM and NH3-TPD showed that when the molar ratio of Zr/Si was 0.02,the crystallization temperature was 120 °C,the crystallization time was 72 h,and the roasting temperature was 5 h at 550 °C,the synthesized Zr-MCM-48 mesoporous molecular sieve has a typical three-dimensional cubic structure,the crystal form is perfectly controllable,and the orderliness is strong.Compared with MCM-48 mesoporous molecular sieves,the sample structure of H-Zr-MCM-48 catalyst which prepared by ammonium nitrate solution treatment was not completely destroyed and still had the three-dimensional cubic structure of MCM-48 and had more acidic sites.Compared with Zr-MCM-48 and H-Zr-MCM-48,although Ni/H-Zr-MCM-48 catalyst had some damage in the pore structure,it still maintained the three-dimensional structure of MCM-48 and the total acid amount on the whole had increased.The samples after the activation had more acidic centers than the unmodified samples.The catalytic performance of n-heptane isomerization was studied using H-Zr-MCM-48 and Ni/H-Zr-MCM-48 acidic mesoporous molecular sieves as catalysts.The effects of metal content,reaction temperature,reaction time and reduction temperature on the reaction results were investigated.The experimental results showed that the conversion rate of the heptane isomerization reaction were 44.6%,when the molar ratio of zirconium and silicon was 0.02,the reaction temperature was 260 °C,and the reaction time was 130 min under the same reaction conditions.The supported nickel metal had a great potential for increasing the activity of the catalyst and increasing the yield of the isomerized product.The catalytic activity of Ni/H-Zr-MCM-48 catalyst was better than H-Zr-MCM-48,and the conversion ofn-heptane and the selectivity of isoheptane are 58.3% and 85% respectively for Ni/H-Zr-MCM-48.Besides,Ni/H-Zr-MCM-48 could still have high catalytic activity after the reaction of 6 h.