Post-modification Of TS-1 And Its Application In The Ammoximation Of Cyclohexanone

Titanium-substituted silicalite-1(TS-1)is a microporous zeolite with an MFI-type structure,and its characteristic is of Ti4+ substitution for a small part of the framework Si4+ in silicalite-1.The reaction system of TS-1 with hydrogen peroxide plays a vital role in a series of organic oxidation reactions and has been widely applied in the chemical industry because of the incorporation of titanium into the framework.However,nano-sized TS-1 crystals are rather difficult to be separated from reaction media and TS-1 with large crystal sizes show intra-diffusion limitations.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.In this thesis,TS-1 zeolites with different crystal sizes were synthesized by a hydrothermal method with tetrathylorthosilicalite(TEOS)as Si source,tetrabutylorthotitanate(TBOT)as Ti source,tetrapropylammonium hydroxide(TPAOH)as template and alkali source with a molar ratio of TEOS:0.03 TBOT:0.45 TPAOH:15.5 H2O.The synthesized TS-1 samples were post-treated with ultraviolet(UV)light irradiation at high temperatures to eliminate the silanol groups of TS-1 crystals.Then both synthesized and post-modified TS-1 crystals were used as catalysts in the ammoximation of cyclohexanone.The main results are summarized as follows:The synthesized TS-1 samples with different crystal sizes(0.4 ?m,0.75 ?m,and 1.2 ?m)were cured with UV light irradiation at high temperatures,during which the effects of the wavelength,temperature,and post-treatment time on the catalytic properties of the post-modified TS-1 in the ammoximation of cyclohexanone were systematically investigated.Moreover,both synthesized and post-modified TS-1 samples were characterized by various techniques such as XRD,SEM,UV-vis,XPS,FT-IR,XRF,ICP-AES,N2 adsorption-desorption at 77 K,1H MAS NMR,and 29Si MAS NMR.The results show that under the same reaction conditions,the catalytic activity of TS-1 significantly decreases with increasing its crystal size,indicating the presence of intra-diffusion limitations in the catalytic ammoximation of cyclohexanone.Under the synergy of UV-light irradiation and high-temperature treatment,the silanol groups of TS-1 crystals are reduced,leading to a higher catalytic activity of TS-1 in the ammoximation of cyclohexanone.Furthermore,the crystal size,morphology,and structure as well as the coordination state of Ti species and Ti/Si ratio of the post-treated TS-1 samples are the same as those of the synthesized ones,but the BET surface area and pore volume of the post-modified samples are slightly enhanced.