Study On The Preparation And Catalytic Properties Of Titanium Silicalite-1

Titanium silicalite-1, i.e. TS-1, is an environmentally benign catalyst. The system composed of TS-1 and diluted hydrogen peroxide aqueous solution, i.e. TS-1/H2O2, shows excellent properties in many organic reactions and can overcome the inevitable disadvantages in traditional processes, such as serious pollution,harsh reaction conditions,complicated operation et al. The successful application of the system in catalytic oxidations has been considered to be the milestone in the domain of zeolite catalysis in 1980s. This application, however, has been hindered by heavy carbon deposition in organic reactions which leads to short age of TS-1. As a result,it is of great importance to find ways to prolong the age of TS-1.In this paper,two kinds of catalysts have been made according to the viewpoint of easing down the carbon deposition of TS-1. First of all,TS-1 powder containing less Br?nsted acidic sites was successfully prepared utilizing pretreated TiO2 as titanium source. Furthermore, TS-1/cordierite monolithic catalyst was prepared using the method of washcoating and cordierite as support,which is able to solve the problem of hard separation of powder TS-1 from reaction products. Besides that,this monolithic catalyst is capable of increasing the relative speed between TS-1 and reaction system,which can reduce the resistance of diffusion and make reaction products diffuse outwards from TS-1 much more easily.The effect of molar ratio of Ti:Si,crystallization time and the time of post-treatment by 0.5M HCl aqueous solution was investigated with FT-IR and UV-vis , respectively. The results show that the TS-1 powder using pretreated TiO2 as titanium source contains less Br?nsted acidic sites by comparision with the TS-1 standard sample; the molar ratio of Ti:Si in synthesis has an optimal value;when crystallized for 24h,most of the pretreated TiO2 has incorporated into the TS-1 framework;and it is enough to wash the TS-1 samples in 0.5M HCl aqueous solution for 24h.In our work,the best result of cyclohexanone ammoximation catalyzed by above TS-1 samples is as follows,the conversion of cyclohexanone is 94.04%, the yield of cyclohexanone oxime is 90.13% and the selectivity of the reaction is 95.84%. In the preparation of TS-1/cordierite monolithic catalyst, the effect of coating time and viscosity of solvent was studied and the reason why TS-1 powder could be coated onto the surface of cordierite was analyzed in detail. The results display that, a maximum value of the weight of TS-1 powder coated can be gotten when washcoated 3min each time; and the viscosity of solvent has little effect on the preparation. The result of ultrasonication treatment indicates that the TS-1 coated has a strong combination with the support.Continuous cyclohexanone ammoximation was used to evaluate the properties of the monolithic catalyst. After 117h,the mass of TS-1 decreased from 3.0922g to 2.9702g, the loss of which, i.e. 0.122g, is very small. The age of the monolithic catalyst is longer than TS-1 powder. When the monolithic catalyst activity decreased,the method of increasing the circulation could be applied to improve its catalytic ability.