Post-modification And Characterization Of The Structures Of Lamellar Zeolite Precursors

Zeolites are crystalline materials with extensive application in the environment-friendly chemistry processes. So it is still a great challenge to develop new zeolite particularly with large-pores to meet the needs in processing bulky reactant molecules as both solid acid and redox catalysts. Direct hydrothermal synthesis through designing organic structure-directing agent (SDA) is the most commonly adopted method. Post-modifying the crystalline structures of existent zeolite, in particular, those already having useful commercial application would be an effective alternative among various considerable choices.In this study, we have developed a novel methodology of preparing a large-pore zeolite material through the interlayer-silylation of layered zeolitic precursors. PREFER and PLS-1, two kinds of typical lamellar zeolitic precursors, was post-synthesized with diethoxydimethysilane (DEDMS) as monomeric silylating agent, respectively. Using this method, we have succeeded in converting lamellar precursor into the zeolite structures with larger pore-diameter between the original structure basic units. These interlayer-expanded microporous zeolite materials with large-pore are more stable and structully regular than mesoporous materials.The effect of post-syntheis conditions, crystallizing temperature, nitric acid concentration and Me₂Si(OEt)₂ concentration, on the structure and properties were investigated in details.The most appropriate condition on silyl-FER is as follows, the concentration of nitric acid is 3 M, Me₂Si(OEt)₂/PREFER weight ration is 0.28, crystallizing temperature is 170℃.The most appropriate condition on silyl-CDS-1 is as follows, the concentration of nitric acid is 3 M, Me₂Si(OEt)₂/PREFER weight ration is 0.25, crystallizing temperature is 170℃.The structures of silyl-FER and silyl-CDS-1 were characterized by XRD, SEM, FT-IR, ¹³C CP/MAS NMR, ²⁹Si MAS NMR, TG and so on. The results proved the interlayer-silylation of FER and CDS-1 lamellar precursors, which also proved that silyl-FER and silyl-CDS-1 with more lager pore-diameter, surface area and the same outstanding thermal and hydrothermal stability, compared with original microporouszeolites.The novel titanosilicates with silyl-FER and CDS-1 types were synthesized and characterized by XRD, SEM, FT-IR, UV-vis, ¹³C CP/MAS NMR, ²⁹Si MAS NMR and so on. Finally, the catalytic properties of Ti-containing zeolites were evaluated briefly in the alkene epoxidation with H₂O₂, which resulted that the zeolites didn't show anticipative properties and selectivity. It needs further study.