Synthesis, Structure Modification And Catalytic Properties Of Lamellar MFI Zeolites

The dissertation is aiming at improving the degree of accessibility of the active sites in zeolites, and improving the diffusion rate of bulky reactants or products with larger kinetic diameter inside zeolite channels, which will expand the range of application of zeolites. New Layered ZSM-5, TS-1and Sn-MFI were synthesized or structurally modified further.In the first part of this dissertation, a lamellar titanosilicate (LTS-1) was hydrothermally synthesized by employing a bifunctional surfactant as the structure-directing agent (SDA). The effect of concentration of SDA on the crystallinity of the final product was examined in details, and the catalytic performance of the obtained zeolite sample was investigated in the epoxidation of cyclohexene, cycloheptene, cyclooctene, cyclododecene and propylene. The samples were highly crystalline materials when the concentration of SDA met0.04≤C22-6-6(OH)2/SiO2≤0.08(molar ratio). As-synthesized LTS-1possessed a multilayer structure, which was constructed from a collection of2-nm zeolite nanosheets and interlayer SDA molecules. Removing the intercalated organic species induced irregular layer stacking to a certain extent, leading to intracrystal mesopores of ca.3.2nm in diameter. In the epoxidation of bulky olefin with tert-butyl hydroperoxide (TBHP) as the oxidant, the catalytic performance of the LTS-1and Ti-MCM-41is comparable, and is significantly higher than that of others. In the epoxidation of propylene using cumene hydroperoxide (CMHP) as the oxidant in the innovative CHPO(cumene hydroperoxide propylene oxide) process, the reaction was highly selective independent of titanosilicates, giving PO as the sole product (>99%), but CTS-1,Ti-Beta, and Ti-MWW showed an extremely low PO yield. However, LTS-1was highly active, showing a20%PO yield even higher than that of Ti-MCM-41. Based on TOF, the activity of LTS-1was about four times as high as that of mesoporous Ti-MCM-41, implying that LTS-1with mesoporosity is a promising catalyst useful for the CHPO process.In the second part, interlayer expanded IEZ-ZSM-5with10-membered ring (MR) and12MR pore was prepared by a new postsynthesis method, that is silylating as-synthesized samples with EtOMe2Si-O-SiMe2OEt in1M HCl/(EtOH+H2O). The effects of postsynthesis conditions such as acid concentration, temperature, different organosilanes and their amount and the amount of ethanol on the structure of final samples were investigated in details.The catalytic performance and pore structure of IEZ-LZSM-5were investigated in the alkylation of benzene, m-xylene isomerization/disproportionation, m-hexane cracking.In the alkylation reaction of benzene with isopropanol, IEZ-LZSM-5showed the highest reaction activity and good selectivity to cumene. During the TOS of8h, the catalytic activity of IEZ-LZSM-5decreased very slowly, and the benzene conversion was from57%to60%, while the selectivity to cumene was in the69-74%. In the cracking of the n-hexane, at the same temperature, the activity of IEZ-LZSM-5was higher than that of LZSM-5, due to the stronger acid sites of the IEZ-LZSM-5. IEZ-LZSM-5showed a higher selectivity to propylene should be attributed to12-MR pores formed in IEZ-LZSM-5, which inhibited the occurrence of hydrogen transfer reactions. In m-xylene isomerization/disproportionation reactions, the p/o ratio of IEZ-LZSM-5and LZSM-5droped between the Beta and CZSM-5, and the p/o ratio of IEZ-LZSM-5is smaller than that of LZSM-5. The i/d ratio changed in descending order: CZSM-5> LZSM-5> IEZ-LZSM-5> Beta. These results are highly correlated with their pore and channel structure.In the third part, layered titanium silicalite LTS-1-PS was synthesized by liquid-solid isomorphous substitution reaction with H2TiF6. Various synthetic conditions such as temperature, time of isomorphous substitution reaction, type of precursor, solid-liquid ratio, ratio of titanium to silica and the amount of acid used for pretreatment of the precursor were investigated. The catalytic activity of the samples was examined n the epoxidation of n-hexene and cyclohexene. LTS1-PS and conventional of TS-1showed a considerable activity, but in the epoxidation of cyclohexene using TBHP as the oxidant, LTS-1-PS showed far higher activity than that of the latter. Meanwhile, an interesting phenomenon was observed, in the epoxidation of n-hexene and cyclohexene using30%H2O2as the oxidant, LTS-1-PS exhibit higher activity than that of samples hydrothermal synthesized, which may be attributed to more hydrophobic surface of the former.In the fourth part, layered Tin-silicalite LSn-MFI-PS, which included LSn-MFI-SLR and LSn-MFI-SSR, was synthesized by liquid-solid isomorphous substitution or solid-phase ion-exchange. Various synthetic conditions such as type of precursor, ratio of Tin to silica and the reaction medium were investigated. The catalytic activity of the samples was examined in the B-V oxidation. LSn-MFI-PS-SLR synthesized by liquid-solid isomorphous substitution showed a slightly higher than that of LSn-MFI-PS-SLR synthesized by solid-phase ion exchange, which should be attributed to more tetrahedral coordination Sn in the former.