Theoretical Studies On The Structures And Catalytic Activiteis Of Framework Incorporated MFI Type Zeolite

Both zeolite ZSM-5 and zeolite TS-1 belong to MFI type, and the only difference between them is the substitution of framework Si by Al or by Ti. However, the catalytic and reactive properties of these two zeolites can be almost totally different. Zeolite ZSM-5 is a good shape selective catalyst in petroleum refining and chemical industry, whereas zeolite TS-1 is used as an excellent selective oxidation catalyst. Combining NMR experiments with theoretical calculations, the present work was carried out to study the properties, adsorptions and reactivities related to these two zeolites, with the main findings summarized below:1. By 27Al MAS NMR, 27Al 3Q MAS NMR experiments and density functional calculations, the mechanism is proposed why La and P can contribute to the enhancement on the hydrothermal stability of ZSM-5 zeolite. Moreover, the electrostatic potential is found as one effective parameter to measure the hydrothermal stability.2. Four representative surfaces were selected to explore the differences of different ZSM-5 zeolite surfaces. The larger the reactant molecule, the more dependent to the zeolite surface. Such a rule is believed applicable to other zeolites besides ZSM-5.3. There are four framework Ti species existing in TS-1 zeolite, including the new defect site designed by us. This defect site can provide Bronsted acidic proton to the adsorbed molecule, which is consistent with our NMR experiments. Meanwhile, silicalite-1 was confirmed to have no Bronsted acidic protons.4. There are two competing reaction pathways for styrene oxidation over TS-1 zeolite: radical and epoxidation. Combing with theoretical calculations, the peaks...