Preparation of Tungstic Oxide supported on sba-15 for metathesis of 1-hexene

Abstract

A mesoporous SBA-15 material was synthesized under acidic condition by using trilock copolymer, Poly(ethylene oxide)-Poly(propylene oxide)-Poly(enthylene oxide), as the pore directing agent in order to use as support for preparation of a new metathesis catalyst, WO₃/SBA-15. The supported catalysts with various tungsten contents were prepared by impregnation of the support with a solution of sodium tungstate via incipient-wetness method followed by calcination at the temperature of 500℃ for 10 hours. The supported catalysts and the synthesized support, which was not loaded with tungsten, were characterized using X-ray diffractometer, scanning electron microscope, nitrogen adsorptometer, diffuse reflectance ultraviolet spectrometer and Raman scattering. It is found that the synthesized SBA-15 support has hexagonal structure, rope-like morphology and high surface area. Crystallinity and surface area of SBA-15 are reduced when it was loaded with tungsten. However, rope-like morphology of SBA-15 still remained. High surface area of SBA-15 results in high dispersion of tungsten oxide, particularly at tungsten loading less than 5%. This is accounted for no observation of WO₃ cryatallite by Raman scattering and diffuse reflectance ultraviolet techniques. The optimal reaction temperature was investigated over the range of 100-500℃ by using 5% of WO₃/SBA-15 as catalyst and 30.5% 1-hexene vapor in nitrogen as feed. The optimal reaction temperature for metathesis reaction of 1-hexene is 300℃ while providing the moderate and highest selectivity to ethylene and propylene, respectively. At 300℃, the selectivity to ethylene and propylene increases with increasing the loading amount of tungsten on SBA-15.