Study On Preparation And Characterization Of Nitrogen-incroporated MWW-type Zeolites And Their Catalytic Properties

Solid acids are expected to replace liquid acids to develop environment friendly reactions, some of which have already been industrialized. However, the studies about solid bases are not so many. Solid base catalysts possess high activity and selectivity under mild reaction conditions. They are easily separated from reaction systems and can be recycled for reuse. The solid bases that may develop green reactions are considered to be a new kind of enviroment-friendly catalyst. Among solid bases, zeolites arouse great interest because of their high surface area and high selectivity. The eralier method to synthesis base zeolite is to introduce strong alkaline objects onto the surface, which would destroy zeolite framework and lower the surface area. Nitrogen atoms and sulphur atoms were introduced to subtitute the oxygen atoms in zeolite framework and increase Lewis basity. Up to date, MWW zeolite containing N atoms have not been reported. At high temperature, ammonia gas is so active to replace the 0 atoms with N atoms. The present work has carried out the synthesis of MWW zeolite with high N content, and investigated its catalytic properties as solid base catalyst. This thesis follows into four parts.Section 1 Synthesis of MWW zeolite with high N contentMWW zeolite containing unstable B atoms was subjected to nitridation at high temperature by solid-gas reation with NH3. MWW zeolites with different N content (0.2-3.5 mmol·g-1) were synthesised by changing the flow rate of NH3, reaction temperature and treatment time. The effect of B content on the nitrogen incorporation into B-MWW was also studied. After nitridation at high temperature, MWW zeolite possessed high crystallinity as confirmed by XRD measurement. The most important thing was that Si-NH-Si species emerged, evidenced by FT-IR, elementary analysis and NMR, which proved N atoms were introduced into the framework of MWW zeolite effectively.Section 2 Investigation of catalytic properties of N-B-MWW-Cal.The synthesized N-B-MWW zeolite was used as the catalyst of the Knoevenagel condensation reaction. The effects of solvent, reaction temperature, reaction time, N content and B content were investigated. The activity of catalyst in Knoevenagel condensation reaction depend on not only N content but also B content.Section3 Synthesis and characterization of N-ERB-1 and N-MCM-22 with acid-base bifunctions.EBR-1 containing both unstable B and Al atoms was used as the precursor for nitridation. N-H-EBR-lwith different N content (0.75-3.02 mmol·g-1) was obtained through the gas-solid reaction with NH3 at 973 K. The IR spectrum showed that a band at 3340 cm-1, which confirmed the existence of Si-NH-Si species. It was used to catalyze Knoevenagel condensation reaction (DMF as solvent at 333 K), the conversion of which reached 86% in 5 min much higher than H-EBR-1 without N atoms (25%) and N-De-B-MWW without strong acid sites (64%).Section 4 The effect of introducing Ti species into alkaline zeolite.Ti-MWW zeolite, synthesized by CVD method, was subjected to nitriding at high temperature. And its catalyst ability was investigated in the epoxidation of olefins.