Preparation Of MCM - 48 Mesoporous Molecular Sieve And Its Application In Propane Dehydrogenation

A series of chromium containing MCM-48 mesoporous molecular sieves were prepared by co-template direct hydrothermal process. The catalytic behavior of the samples was investigated in the dehydrogenation of propane to propylene in the presence of CO2 at 600℃. The catalysts were subsequently characterized by BET surface area, X-ray diffraction(XRD), FT-IR, NH3-TPD, H2-TPR and X-ray photoelectron spectra(XPS) as well as measurement of the catalytic performance. These results show that Cr3+ ions are incorporated into the lattice of MCM-48 during synthesis instead of accumulating in pores to provide surface active sites. Chromium species improve the catalytic properties of the metarial in the dehydrogenation of propane. The Cr ions substituted Si molers into the Silica framework, accordingly the performance of the molecular sieves catalyst has been improved.Simultaneously, Na F was added to the solution among the hydrothermal process to control the hytrolysis of TEOS, improve the velocity of the crystallization process. The catalysts performance in the dehydrogenation of propane in the presence of CO2 was researched too. The chemical and physical characterization including BET surface area, X-ray diffraction(XRD), FT-IR, NH3-TPD, H2-TPR and X-ray photoelectron spectra(XPS) and so on. The results illustrate that the catalysts showed better physical performance with the addit ion of Na F. Thus, it expressed much better chemical and catalytic performance.Meanwhile, a series of dehydrogenation reactions were setted off to find the best doping content of chromium made by different preparation methods for the high catalytic performance. For the co-template method, Si/Cr=70 is the best ratio to reach the best catalytic property. However, Si/Cr=80 is the best ratio to the other method. The propane conversion and propylene selectivity of the above two methods can reach 45% and 91% respectively.