Studies On W-based Catalyst For Metathesis Of Ethylene And1-butylene To Propylene

The demand for propylene has grown quickly, since it is an important petrochemical feedstock. Therefore, the utilization of industrial excessive butene and ethylene to produce valuable propylene by metathesis reaction has a remarkable economic implication and social benefit. W-based catalysts are reactive and antitoxic, attracting much attention for employing this kind of catalysts to produce propylene by metathesis. In this work, the effect of promoter and pretreatment of WO3/SiO2catalyst as well as the reaction condition for C4olefin metathesis to improve the activity of catalyst, and mesoporous carrier effect on catalyst performance had also been investigated. The optimized catalyst is examined in pilot demonstration to provide data for industrial application.The influence of the catalyst pretreatment gas was investigated. Five different pretreatment gases (air, N2,1/9H2/N2,1/1H2/N2, H2) were employed to pretreat WO3/SiO2catalysts before reactions, and comprehensive characterizations by XRD, BET, Raman, UV-Vis, TGA, FT-IR, TEM, XPS and H2-TPR techniques were carried out. After air pretreatment catalysts, the monoclinic WO3was very stable in the reaction and difficult turn into active phase tetragonal. Although the catalysts of treated with nitrogen was also monoclinic phase WO3, it was easily converted into an active phase in the reaction, and the emergence of part W5+species. It was found that the W5+species occurred by reduction of WO3/SiO2catalysts with N2and H2, and the content of W5+species was controlled by the pretreatment gases. Combined with the catalyst activity of preatment catalysts, it was concluded that W5+species can improve the catalytic activity, suggesting that the active species of the catalyst WO3/SiO2was the intermediate oxidation state and located between WO3and WO2.92.Tungsten-doped mesoporous W-KIT-6have been successfully synthesized. The studies of small-angle XRD, BET and TEM illustrated that the3D ordered mesoporous structure and their high surface area of KIT-6were maintained in W-KIT-6. The catalytic performance of doped W-KIT-6was much better than those of supported WO3/KIT-6and WO3/SiO2catalysts.