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Study On The Synthetic Process Of Titanium Silicalite And Its Catalytic And Oxidative Performance

Posted on:2004-03-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:L Q WangFull Text:PDF
GTID:1101360095955247Subject:Industrial Catalysis
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Titanium Silicalite-1 (TS-1) is a new kind of catalytic material, which has unique MFI topological structure. In 1983, TS-1 was synthesized first by Enichem in Italy. The system of TS-1 and H2O2 exhibits excellent catalytic and oxidative performance in the mild reaction conditions, so it has been paid more attention by many researchers at home and abroad. The above process has overcome the shortcomings of serious pollution and unsafe factors of traditional oxidative ones, and it has provided new pathways for the green chemical engineering and environmentally friendly processes. Synthesis, characterization and industrial applications of TS-1 have become very important parts in the field of zeolite catalysis. In the past twenty years, many improvements have been made, which include decreasing the synthetic costs, enhancing the preparing repetition, decreasing the amount of anatase TiO2 and expanding its industrial applications.Based on the traditionally hydrothermal synthetic methods, we have put forward to two kinds of TS-1 quick synthsis methods with self-made aqueous TPAOH solution as template. One method is to modify the titanosilicon sol preparation step; the other one is in the presence of a little amount of Tween series as nonionic surfactants. Catalytic performances of TS-1 samples are investigated in the propylene epoxidation and phenol hydroxylation as probe reactions. Comparing the two synthetic methods of TS-1 with TPAOH and with TPABr as template, we have recognized the similarities and differences between the two methods; some correlative explanations have also been given here. The above research works help us to further understand the synthetic process and its influencing factors and accumulate the basic research data for TS-1 industrialization. The contents of the dissertation in details are as follows: 1. Quick hydrothermal synthesis of TS-1In the titanosilicon sol preparation step, we use TPAOH (~20 wt %) as template and make TEOS and TBOT full hydrolysis, respectively, then mix them, after 1-6 h alcohol removal and within 24 h crystallization, Nanometer-scale TS-1 samples have been obtained with good preparation repetition. XRD, TEM/SEM, FT-IR, UV-Vis, XRF, BET, TG, DTG and other characterization have been used to study TS-1 crystallization process systematically. The results show that SiO2-TiO2 co-gel exists in the synthetic system at first, crystallization becomes quicker after 1 h, the relativecrystallinity of TS-1 samples is near 90 % after 5 h and it is up to the highest point near 20 h. The morphology of TS-1 samples is cubic shape and the crystal sizes are about 100 nm. Then, the molecular sieve structure is near stable. With the crystallization process going on, Ti atoms are gradually incorporated into the framework structure, the characterizations lie in: unit cell parameters and volumes increase linearly, pore volumes and specific surface areas increase little by little, the molar SiO2/TiO2 ratio in products tends to the value in feeds, the vibrational bands at near 960 cm-1 in FT-IR spectra become stronger and stronger, pH value of TS-1 liquor has increased to the highest point distinctly between 2-5 h crystallization, meanwhile, the framework structure of molecular sieve come into being quickly, which means the TS-1 framework formation is consistent with the pH value rapid increase in the liquor.The concerned kinetics in the TS-1 quick crystallization has also been investigated. The results show that the induction period is short, and the rates of nucleation and crystal growth are large. The calculated apparent activation energies of nucleation and crystal growth are 33.60 and 36.73 kJ/mol, respectively, which are a little smaller than that of traditionally hydro thermal synthesis. The crystallization becomes quicker with temperature increase. We have found that quick crystallization is based on the typical liquid mechanism. In the strong base environment provided by TPAOH, there are high concentrations of low polymeric silicon and titanium species existing from TEOS a...
Keywords/Search Tags:Titanium Silicalite-1 (TS-1), quick synthesis, crystallization dynamics, physicochemical properties, nonionic surfactant, propylene epoxidation, phenol hydroxylation
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