Synthesis Of Hierarchical TS-1Zeolites And Its Catalytic Application In Phenol Hydroxylation Reaction

There is a series of excellent properties of TS-1zeolites, such as shape-selectivity, hydrothermal stability and selective oxidation. Therefore, they can be widely used in lots of catalytic oxidation reactions. TS-1zeolites have very high catalytic activities in selective oxidation reactions of lots of organic compounds, when using H2O2as oxidant under mild conditions. However, because of its small micropores, TS-1suffers from obvious diffusion limitation. When related to the reactions with bulky reactants and products, this limitation is very pronounced. In bulky molecules reactions, in order to solve the problems of diffusion limitation, hierarchical zeolite is very effective.The synthesis steps of Hierarchical TS-1zeolites reported in literatures are complicated, which goes against their industrial application. Herein, we use a new method called quasi-solid phase conversion method to synthesize hierarchical TS-1zeolites. The synthesis process includes just one step and no additional template added. By XRD, SEM, TEM, N2absorption-desorption, UV-vis diffuse reflectance, TS-1zeolites are characterized. Subsequently, we study the influences of synthesis conditions, such as crystallization time, crystallization temperature, water content, Si/Ti, TPAOH content and alcohols. Finally, to study the effects of the mesopores, we use the TS-1zeolites for the catalytic oxidation of phenol.The results have shown that the crystallization time plays an important role in the synthesis process of hierarchical TS-1zeolites. In the synthesis process, the first step is the formation of microporous zeolite TS-1and then mesopores. With the increase of crystallization time, mesopore content in hierarchical TS-1zeolites increases and pore size becomes uniform gradually. Besides, water content is also a critical factor. When water content is moderate, we can get hierarchical TS-1zeolites with fine crystallinity. When the zeolite precursors are with low water content, we can get amorphous titanium silicate. When the water content is high, microporous TS-1zeolite will be produced. The crystallinity of hierarchical TS-1zeolites is increasing while the ratio of Si/Ti is increasing. The hydrolytic process of siloxane can be stabilized by adding alcohols, which can promote interaction between silicon source and titanium source. The mesopores in hierarchical TS-1zeolites can slow down the formation rate of byproduct of phenol tar in the reaction of hydroxylation of phenol. The conversion rate of phenol applied hierarchical TS-1zeolites can be increased by16.71%compared with micropores TS-1. The selectivity of target product of benzenediol can be increased by15.87%.