Synthesis Of Novel Heteroatom Zeolites And Study On Their Catalytic Performances

As an inorganic porous material,zeolites with high thermal/hydrothermal stability,large surface area and excellent acid-base catalytic performance,are widely used in chemical production field.So far,more than 250 types of zeolites structures are published by Structure Commission International Zeolite Association.Among them,Ge-zeolites,with large s pore structures,have shown great potential for application in the field of catalytic conversion of macromolecular substrates.However,Ge-zeolites are problematic because the easy degradation of its structure.So,few practical applications of have been reported.In this paper,novel zeolites containing heteroatoms with stable structures were designed and synthesized from germanosilicates UTL and*CTH by taking advantage of their structural instability.Meanwhile,the catalytic activity of the novel zeolites in the relevant reactions was investigated in detail.1.Shape-selective stannosilicates have been post-synthesized for the hydration of epoxide to diols.A simple acid treatment has been employed to remove extensively the interlayer double four ring units,converting the three-dimensional(3D)UTL germanosilicate into a 2D layered IPC-1P intermediate.Isomorphous incorporation of tetrahedrally coordinated Sn active centers was realized via solid-liquid treatment of IPC1P with diammonium hexachlorostannate aqueous solution,which was accompanied by the spontaneous condensation of neighboring silica-rich cfi layers upon calcination and structural construction of a 3D PCR structure.Sn-PCR stannosilicates with tunable Sn contents were thus prepared.With Sn-derived robust Lewis acidity confined in the intersecting 10-and 8-ring channels,the Sn-PCR(Si/Sn molar ratio of 77)catalyst served as a shape-selective nanoreactor for the hydration of ethylene oxide(EO)into ethylene glycol(EG),exhibiting a remarkable EO conversion(99.5%)as well as a steady EG selectivity(>98.4%)at greatly reduced H2O/EO molar ratio and near-ambient reaction temperature.2.Germanium-rich*CTH zeolite without organic molecules located inside pore channels experienced only partial structural collapse and subsequently repaired to highsilica structure analogous to the original topology in a short time.The surprise acidhydrolysis process has caused a large amount of framework Ge ions were removed,giving rise to abundant hydroxyl nests.Benefiting from the unexpected variation of framework structure and chemical composition,stannosilicates Sn-*CTH with extra-large pores and various Sn loadings(Si/Sn molar ratio in the range of 3 0-∞)were post-prepared depending on the reaction between the added(NH4)2SnCl6 species and the formed silanol groups in the hydroxyl nests.The resultant Sn-*CTH zeolites were able to release significantly the diffusion limitations encountered by the bulky substrates and oxidants,exhibiting promising activities to catalyze the Baeyer-Villiger(B-V)oxidation of ketones with single oxidant either hydrogen peroxide(H2O2)or large-sized tert-butyl hydroperoxide(TBHP).Especially,high ε-caprolactone product selectivity was also obtained in the B-V oxidation of cyclohexanone using H2O2 oxidant through reducing the H2O2/cyclohexanone molar ratio as well as controlling appropriate reaction time,which was more efficient than the traditional Sn-Beta-F.3.The calcined UTL was treated with ultrasound in order to remove the Ge-rich d4r and make the regular cfi layers occur disorderly stacking.Finally,giving rise to UTL-S sample.The removal of Ge atoms created a large number of defective sites in the UTL framework.Meanwhile,part of cfi layers occurred disordered stacking make UTL-S obtain a more open structure.Subsequently,Co-UTL-S-X,a more stable and open-pore cobaltcontaining zeolite,was prepared by the introduction of cobalt into the UTL-S using cobalt nitrate hexahydrate as the cobalt source.In which Co-UTL-S-5 showed excellent catalytic performance in the reaction of styrene epoxidation to ethylene oxide.The conversion frequency(TOF)exceeded 376.2 molstyrene·mol-1metal·h-1 and the styrene conversion reach 77.2%as well as the ethylene oxide selectivity to more than 67.2%within 2.5 h.The simple sonication strategy opens up new ideas for the stabilization and tuning of the structure of Ge-zeolites.