The Hydrophobic And Hierarchical Modification Of TS-1 For Propylene Expoxidation

The propylene expoxidation,catalyzed by TS-1,has the advantages of high selectivity,mild conditions,environment protection.However,the diffusion limitation by narrow micropores of TS-1,frequently leads to carbon deposition in catalytic applications.In order to solve this problem,the study was carried out by designing the hydrophobic and hierarchical modification of TS-1.Firstly,the hydrophobic and hierarchical TS-1 was prepared by desilication and silanization of TS-1 in NaOH solution and trimethylchlorosilane solution,respectively.The hydrophobic and hierarchical TS-1 was characterized by BET,TEM,XRD,FT-IR and contact angle images.BET and TEM images demonstrate the hierarchical channel structures in the modified zeolites,conbined by micropores of 0.55 nm and mesopores of 3.90 nm.XRD and FT-IR results show that the modified zeolites remain the MFI topology.The contact angle images indicate that the modified zeolites are hydrophobic.The effects of NaOH and TMCS concentrations on catalytic activity were studied.The modified catalyst shows good catalytic activity when Na OH concentration and TMCS concentration are 0.4 M and 25 wt.%,respectively.Secondly,the effects of reaction conditions on propylene epoxidation of the TS-1-0.4M-25%(the hydrophobic and hierarchical TS-1 is prepared when the concentrations of Na OH solution and TMCS solution are 0.4 M and 25 wt.%,respectively)were studied.The factors of rotation speed,reaction time,reaction pressure and reaction temperature were investigated.When the rotation speed is 700 r·min-1,the reaction time is 1.5 h,the reaction pressure is 0.4 MPa and the reaction temperature is 40 ?,H2O2 conversation,PO selectivity and PO concentration reach 99.72 %,91.33 % and 0.85 mol·L-1,respectively.Finally,primary discussion for the mechanism of desilicication process and silanization process was progressed according to the characterization of zeolites.It shows that treatment of TS-1 by desilication in aqueous NaOH solution resultes in mesopours,while TMCS reacts with surface Si-OH to form-O-Si(Me)3.The pore diameters,which were calculated by Materials Studio,are consistent with the characterization of the modified zeolites.The study proves that the hydrophobic and hierarchical modification of TS-1 is feasible for propylene epoxidation with high catalytic activity.The research would provide a theoretical basis for industrial application of the innovative catalyst.