Synthesis of Chromic Oxide and Molybdic Oxide supported on Mesoporous Silica using direct impregnation method and their catalytic activities
This research describes further development of the direct impregnation method for synthesis of chromic oxide and molybdic oxide supported on the mesoporous silica molecular sieve (MCM-41) for use as a solid acid catalyst. The catalysts were characterized by powder X-ray diffraction (XRD), thermo gravimetry (TG), Fourier transform infrared spectroscopy (FTIR) and surface area measurement using N2 isotherm adsorption techniques. Solid super acid catalysts are important industrial catalysts. By addition of the metals Cr and Mo to the mesoporous MCM-41silica structure, solid super acid catalysts can be prepared. Both Brønsted and Lewis acid sites are formed which are responsible for the catalytic activities. Compared with the traditional solid acid catalysts and transition metals, the modified MCM-41 molecular sieve has a larger specific surface area and better hydrothermal stability. A direct impregnation method has been developed to explore the positive characteristics of the materials discussed above. After calcination, all the samples exhibited the typical hexagonal arrangement of mesoporous structures with large surface area and the heteroatoms partly incorporated into the framework of MCM-41. The results showed up to 50 percent metal oxide : silicate ratio of transition metal can be loaded into the framework of MCM-41. By the addition of Cr and Mo, two groups of new catalysts were prepared which had higher activity and selectivity than MCM-41 when evaluated using the condensation esterification of acetic acid and n-butanol. Further, the catalysts could be regenerated and reused by calcination.