| Titanium-substituted silicalite-1(TS-1)with an MFI topology framework is of microporous zeolite that is the substitution of Si4+ by Ti4+ in the framework of silicalite-1.The reaction system of TS-1 with hydrogen peroxide plays a vital role in a series of organic catalytic oxidation reactions and has been widely applied in the chemical industry.However,nano-sized TS-1 crystals are rather difficult to be separated from reaction media and TS-1 catalysts with larger crystals show intra-diffusion limitations in their applications.Therefore,it is of utmost importance to develop a method to improve the intra-diffusion limitations of TS-1 crystals in order to solve the problems associated with the industrial applications of nano-sized TS-1 crystals.The research work of this thesis includes the synthesis of TS-1 with different crystal sizes by a hydrothermal method,the post-treatment of the synthesized samples with ultraviolet(UV)light irradiation at a high temperature,and the catalytic reaction performance of both untreated and treated TS-1 catalysts in the ammoximation of cyclohexanone.The main results and conclusions are summarized as follows:1.TS-1 samples were synthesized by a hydrothermal method with tetrathylorthosilicalite(TEOS)as Si source,tetrabutylortitanate(TBOT)as Ti source,tetrapropylammonium hydroxide(TPAOH)with alkali-free as template with molar ratios:TEOS:TBOT:TPAOH:H2O=1X:0.45:Y(X=0.02-0.035;Y=15-35).Various synthesis parameters such as the molar ratio of Si to Ti,exhaust-alcohol time,rotation speed in crystallization,and used dosage of water in the synthesis solution,affecting the crystal size and morphology as well as the Ti species of the resultant TS-1 samples,were systematically investigated.Then the synthesized TS-1 samples were characterized by XRD,SEM,UV-vis,and FT-IR techniques.The results show that pure TS-1 samples with tetrahedrally coordinated Ti species in the framework,almost without non-framework Ti species(such as hexa-coordinated Ti and anatase),and with spherical or hexagonal prism crystals with sizes ranging from 0.2 to 1.2 ?m,have been successfully synthesized.2.The synthesized samples were cured with UV light irradiation at a high temperature,which is described as follows:the TS-1 sample was first placed into a heating cavity set inside a UV-assisted high-temperature reactor and then the cavity was rapidly heated up to 425 ? under vacuum,finally the sample was exposed to UV light irradiation with wavelengths ranging from 200 to 400 nm for 10 min.The untreated and treated TS-1 samples were characterized by XRD,SEM,UV-vis,FT-IR,and XPS techniques.The results of XRD snd SEM characterizations show that the crystal size and morphology of the treated TS-1 samples are the same as those of the untreated ones.The FT-TR characterization shows that the absorption intensity at 3600-3200 cm-1,assigned to H-bonded silanol groups,for the treated TS-1 sample is significantly decreased,suggesting that most silanol groups could be disappeared by the UV-assisted curing at the high temperature.In addition,the UV-vis characterization shows that the absorption intensity at 210 nm,assigned to tetrahedrally coordinated Ti species in the framework,for the treated TS-1 sample is obviously enhanced,and in combination with the FT-IR characterization result,it is speculated that the silanol groups of the synthesized TS-1 sample could be disappeared by the UV-assisted curing and Ti-O-Si bonds could be formed simultaneously.3.The untreated and treated TS-1 samples were used as catalysts in the ammoximation of cyclohexanone.The results indicate that the treated TS-1 catalyst shows a higher catalytic activity and selectivity for cyclohexanone oxime than the untreated one.In addition,the UV-assisted curing of the TS-1 catalysts with large crystal sizes can more significantly enhance the catalytic activity and selectivity in the ammoximation of cyclohexanone. |
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