Study For Synthesis Of Titanosilicate MWW Structure Zeolite And Its Catalytic Performance

Titanosilicate MWW structure zeolite exhibited excellent catalytic activity in the epoxidation of alkene due to its unique crystal structure and pore system and displayed significant academic value and industrial application prospects in the green chemical reaction process.In this paper,titanosilicate MWW structure zeolites were synthesized with boronsilicate MWW zeolite ERB-1 as precursor using inorganic or organic titanium sources by grafting,atom-planting method,respectively.The crystalline and pore structure of the zeolites and the existence forms and content of titanium species were characterized by X-ray diffraction?XRD?,nitrogen adsorption and desorption test?BET?,fourier transform infrared spectroscopy?FTIR?,solid ultraviolet-visible diffuse reflectance spectroscopy?UV-Vis?,scanning electron microscopy and electron spectroscopy?SEM-EDS?,ultraviolet raman resonance spectroscopy?UVRRS?.Comparing the catalytic activity and efficiency of Ti-containing catalysts in hydrophilic and hydrophobic systems through 1-hexene epoxidation with hydrogen peroxide as oxidant and cyclohexene epoxidation with tert-butyl hydroperoxide?TBHP?as oxidant to investigate the catalytic active sites and structure characteristics of the catalysts for alkene epoxidation.A series of titanosilicate MWW zeolites G-Ti-D-ERB-1 were synthesized with different titanium sources of tetrabutylortho titanate?TBOT?and tetra isopropyl titanate?TIPT?and changing the Si/Ti molar ratio of zeolite precursor to titanium sources by grafting method.The effects of the titanium source,grafted titanium content and calcination to the structure of zeolites and catalytic activity of cyclohexene epoxidation with TBHP were compared.The results showed that the basic MWW structure and pore system of ERB-1 precursor would not be destroyed by acid treatment and titanium loading.The catalytic activity of 50G-Ti-D-ERB-1 without calcining was the highest.The conversion of cyclohexene epoxidation was52.21%and the selectivity was 96.32%.The catalytic performance of titanosilicate MWW structure zeolites synthesized by atom-planting and grafting method,MFI structure titanosilicate TS-1 and anatase were compared by using 1-hexene H₂O₂ epoxidation and cyclohexene TBHP epoxidation as model reactions.The results showed that with the exception of TS-1 and Ti-D-ERB-1synthesized by atom-planting,which both contained tetrahedrally coordinated titanium species,anatase and G-Ti-D-ERB-1 which synthesized by grafting showed little 1-hexene conversion,indicating that the tetrahedrally coordinated framework titanium species are the catalytic active sites;TS-1 was limited by its relatively narrow pore structure system showed no catalytic activity in the cyclohexene TBHP epoxidation reaction,and the synthesized titanium-containing MWW zeolites show excellent catalytic activity for the unique supercage structure,up to 52.03%.The coordination state and the content of titanium species implanted to the zeolites can be adjusted by changing the atom-planting treatment temperature,treatment time and the saturated vapor pressure of titanium tetrachloride?Ti Cl₄?when synthesizing titanosilicate MWW structure zeolites by atom-planting.At 573 K,the synthesized Ti-D-ERB-1-L series sample,titanium species coexisted in the form of tetrahedral and octahedral coordination,contained more titanium content and showed higher catalytic activity for alkene and the conversion of 1-hexene and cyclohexene can reach 35.16%and 41.02%respectively.At 773K,the synthesized Ti-D-ERB-1-H series sample,titanium species existed mainly in the form of tetrahedral coordination,had higher catalytic efficiency and better selectivity of the epoxy products of cyclohexene.The selectivity can reach 95%.With the prolongation of reaction time,no matter high temperature series sample or low temperature,the conversion of alkene increased with the increasing of the amount of titanium in zeolite.When the treatment time reached 9 h,the cyclohexene conversion could reach 26.04%.