A Study On Synthesis,Chemical Modification And Catalytic Performance Of Mse-type Titanosilicate

Zeolite plays an important role in the petrochemical industry because of its specific acidity and shape selectivity.Isomorphous substitution of titanium atoms into zeolite framework could endow with the catalytic ability of selective oxidation for a variety of organic substrates,and this kind of metallosilicate is named titanosilicate.The titanosilicate/H2O2 catalytic system has drawn much attentions with the feature of high atomic economy and environmental friendliness.In this study,we attempted to optimize the preparation of MSE-type titanosilicate?Ti-MSE?and to improve its catalytic activity by chemical modification.In the first part,we hydrothermally synthesized MSE-type aluminosilicate UZM-35 using commercially available DMDPAOH as SDA in the presence of a suitable amount of MCM-68 seeds.By virtue of this new route,the operation window of sol-gel composition was significantly widened,and the crystallization period was shortened obviously.Besides,the framework of the obtained UZM-35 kept intact in deep dealumination process.Ti-UZM-35,synthesized by solid-gas reaction between highly dealuminated UZM-35 and TiCl4 vapor,exhibited high catalytic activity and para-selectivity in the phenol hydroxylation,which were comparable to those Ti-MCM-68.In the second part,with purpose to improve the activity of Ti-UZM-35 in cyclohexanone ammoximation,the fluorination modification of Ti-UZM-35 was conducted in the NH4F/methanol system.Under the optimal fluorination conditions of423 K,F/Si=0.02,the ammoximation activity of Ti-UZM-35 was obviously improved.The further study proved the generation of SiF6^2-specie during the fluorination modification process,it could lead to the transformation of the close Ti site to open Ti site and finally resulted in the enhancement of catalytic activity.