Fluorinated TS-1 Prepared By Microwave Irradiation And Its Catalytic Performance

TS-1 is a titanium-silicon molecular sieve with MFI structure.Due to its variable valence state of titanium atoms,TS-1 exhibits remarkable catalytic performance in a series of selective oxidation reactions with low concentration of H₂O₂ as oxidant under mild conditions.The core of the TS-1 catalytic reaction is that the active center Ti⁴⁺ reacts with H₂O₂ to form the active center Ti-O^?-O^?-H.Enhancing the Lewis acid strength of the active center Ti⁴⁺ can reduce the energy barrier with H₂O₂ to form Ti-O^?-O^?-H.Thereby,the ability of the TS-1 to activate H₂O₂ is improved,and finally the selectivity of the product is improved.In addition,the catalytic performance of TS-1 is also closely related to its hydrophobicity.At present,the adjustment of the strength of molecular sieve Lewis acid is mainly achieved by fluorine modification: F has been successfully implanted into the framework of Ti-MOR and Ti-MWW by conventional heating methods,and exhibits excellent catalytic activity.However,there are few works on dealing with fluorinated TS-1.Therefore,there is a great value to explore new methods to enhance the catalytic activity of TS-1.Conventional heating is a "outside to inside" heating method.There is a distinct temperature gradient that does not achieve uniform heating.Compared with the conventional heating method,microwave heating has a fast heating rate and uniform heating.Moreover,microwave heating can be selectively heated.In this paper,fluorinated TS-1?F-TS-1-M? was prepared under microwave-assisted conditions with Na F as the fluorine source and dimethyl sulfoxide?DMSO? as the solvent,and compared with fluorinated TS-1 prepared by conventional method?F-TS-1-T?,microwave treated TS-1?TS-1-T? and TS-1.The structure,texture,coordination state of titanium and the existence form of fluorine were characterized by XRD,N₂ adsorption,DR UV-Vis,²⁹Si MAS NMR and ¹⁹F MAS NMR.The results showed that microwave irradiation could promote the transformation of non-framework Ti species to tetrahedral framework Ti,and F-TS-1-M has higher Lewis acidity and hydrophobicity than F-TS-1-T,TS-1-M and TS-1.In the ammoximation of cyclohexanone,F-TS-1-M has the lowest apparent activation energy.Therefore,the catalytic activity of F-TS-1-M is the best in the ammoximation reaction.Under this condition,the influence of the amount of Na F,microwave radiation power,fluorinated temperature and microwave irradiation time on F-TS-1 were investigated.And the physicochemical properties of the catalyst were characterized by various characterization methods,the catalytic performance was also studied.The results showed the amount of Na F added is Si/F=20,the microwave radiation power is 650 W,the fluorine modification temperature is 180 ?,and the microwave irradiation time is 2.0 h,the catalyst exhibited the best catalytic activity.