Effect Of Surface Acidity On WO_x/SBA-15 Catalyst For Olefin Exchange Reaction

Propylene plays an important role in the petrochemical industry.Propylene is used to produce polypropylene,acrylonitrile and other chemical products,which is closely related to our lives.Based on the change of supply and demand relationship of propylene,domestic propylene production capacity can not meet the huge gap in the market.In this paper,the supported tungsten O_xide catalyst was used in the reaction of olefin decomposition to propylene,and the activity of the catalyst was evaluated by fixed bed evaluation device.The texture properties,coordination and acidity of the samples were characterized by XRD,N₂adsorption desorption,TEM,Raman,H₂-TPR,NH₃-TPD and so on.Through literature research,I found that the surface acidity of the catalyst is closely related to the acidity of the catalyst,and the relationship between the micro chemical environment in the molecular sieve and the catalytic performance of the catalyst does exist.However,the current literature reports are limited to the discovery of phenomena;The effect of surface acidity on the catalytic activity of zeolites is not clear;How the active sites on molecular sieves and metal ions play a synergistic catalytic role.Therefore,the correlation between the surface acidity of WO_x/SBA-15 Catalyst and the structure-activity relationship of olefin exchange reaction was studied.X-ray powder diffraction was used;Nitrogen adsorption desorption;The catalysts were characterized by temperature programmed desorption（TPD）of ammonia and Raman spectroscopy.These studies can provide theoretical basis for the design of new olefinmetathesis catalysts,and provide new ideas and ideas for the research and development of olefin cross metathesis catalysts.The purpose of this paper is to prepare tungsten based catalysts（HY,Na Y,USY,etc.）supported by different carriers by regulating carriers.By comparing the acid acid level differences between carriers,the relationship between them and catalytic activity is analyzed,so as to screen out whether there are molecular sieves more suitable for carrier than silicon based materials,and provide some reference for the selection of carriers for olefin decomposition to propylene.The aim of this paper is to prepare tungsten based catalysts（HY,nay,USY,etc.）supported on different supports by adjusting the supports.By comparing the acidic sites between supports,it is found that hydrogen transfer occurs in the strong acidic reaction of supports,resulting in poor catalytic activity.The propylene yield of WO_x/USY was less than 5%,and it was inactivated after one hour.WO_x/Na Y and WO_x/HY also showed low catalytic activity.On the basis of the above research,the pure silicon carrier SBA-15was doped with al,At the same time,WO_x/al-sba-15 catalysts were prepared by wet impregnation method with ammonium metatungstate as the active component.The results showed that the introduction of Al species changed the dispersion of WO_xon the supports,The higher the amount of Al species introduced,the better the dispersion of WO_x.the introduction of Al changed the acidity of the sample and brought about B,L acid sites.Combined with the evaluation data of catalytic reaction,it was found that WO_x/SBA-15 had the best catalytic performance,and the propylene yield and selectivity decreased with the increase of Al content.The research of this project is expected to provide a certain basis for the research of surface modification of olefin disproportionation carrier.