Synthesis Of Sn-containing Germanosilicate Extra-large Pore Zeolite And Its Catalytic Performance For Baeyer-Villiger Oxidation

Heteroatom zeolites doped with Sn and Ge have Lewis acidity,showing excellent reactivity in catalyzing B-V oxidation reaction.They can convert ketones into esters or lactones with high selectivity,and have good application prospects.Traditional Sn heteroatom zeolites,such as Sn-Beta,all have 12 membered rings or less,For bulkymoleculars,the accessibility of the catalytic active center is poor,and the catalytic reaction process is limited.Therefore,the development of Sn heteroatom zeolite catalysts with larger pore size has attracted great attention.In this paper,the ITT structure with 18×10×10three-dimensional pore channels was taken as the research object,and the preparation of Sn-containing germanosilicate extra-large pore zeolites catalyst and the catalytic performance for B-V oxidation were studied.Alkyl imidazolium was used as template to synthesize ITT zeolites with different Si/Ge ratios.The physical and chemical properties of ITT zeolites were analyzed by various characterization methods.It was found that the crystallinity,specific surface area and micropore volume of ITT zeolites increased gradually when the Si/Ge ratio decreased.Using 2-adamantanone as model reactant,compared with BEC(three-dimensional 12-membered ring)germanosilicate zeolite,the B-V oxidation catalytic performance of ITT zeolite was studied.The catalytic activity of ITT was superior to that of BEC and increases with the decrease of Si/Ge ratio,which indicates that the extra-large pore structure was beneficial to the diffusion of reaction substrate,the accessibility of active sites was higher.And the high Ge content could improve the apparent catalytic reaction rate.In addition,the2-adamantanlactone selectivity of the reaction could reach more than 98%with 30 wt.% hydrogen peroxide as oxidant,but the ITT structure couldnot remain stable during the reaction due to the presence of water.When tert-butyl hydroperoxide was used as the oxidant,the ITT structure could remain stable,but the reaction selectivity was lower(77%～86%).Sn heteroatom ITT extra-large pore zeolites was prepared with Si/Ge ratio of 2.It is proved that Sn heteroatom was incorporated in the zeolites framework and induced new Lewis acid sites by FT-IR,UV-vis and XPS characterization methods.The crystallinity,specific surface area and micropore volume of ITT zeolites increased first and then decreased with the increase of Sn amount,and the optimum ratio of Si/Sn was 100.Sn-ITT-2-100 showed superior catalytic activity compared with the pure germanosilicate ITT zeolites.