Characterization Of Zeolite Catalyst By FT-IR

Titanium silicalite-1 zeolite is a new material with the MFI structure. Because of its unique performance in selective oxidation, it has been widely applied to many industrial process, Such as phenol hydroxylation, cyclohexanone amine oxidation and propylene epoxidation, and so on. The classic synthesis of TS-1 characterized by TPAOH template, is too expensive for use. Therefore, a cheaper method for TS-1 synthesis using TPABr as template is attractive. But compared to the classic method, it has to endure the lower catalytic activity, especially for propylene epoxidation. Works reported indicate that low-catalytic activity of TS-1 synthesis with cheap template is attributed to much more exframework titanium, as well as large crystal particle. To improve the catalytic activity, Surface silylation technology has been used to enhance the hydrophobic of TS-1, which indicates that the catalytic properties of TS-1 may be related to the surface hydroxyl groups. However, knowledge about the TS-1 hydroxyl is still limited. Therefore, in this paper the infrared spectroscopy (IR) technology is used to study the skeleton structure,hydroxyl groups and surface acidity of the low-cost TS-1. Based on systematic experiments, comparisons of hydroxyl groups of TS-1 between cheap and classic method, O-H types of TS-1 with cheap template by Near-infrared spectroscopy, changes of the hydroxyl groups arid propylene epoxidation of TS-1 after modifications with different sodium salt and alkali, changes of skeleton structure, hydroxyl groups and surface acidity of TS-1 and ZSM-5 catalysts after plasma treatment, have been studied using infrared spectroscopy (IR) technology. The results and conclusions are followings:1. In the complicated hydroxyl groups of the low-cost TS-1 catalysts, not only isolated Si-OH and terminal hydroxyl groups (either external and internal), but also geminal OH groups and hydrogen-bonded hydroxyl groups have been found. For strong internal geminal OH groups and skeleton structure, the low-cost TS-1 catalysts have good thermal stability (1023K). Infrared spectra of pyridine adsorption shows that the strong Lewis acids are much more than weak Bronsted acids in the low-cost TS-1 catalysts. Compared to the low-cost TS-1 catalysts, the classical TS-1 catalysts have simple hydroxyl groups which is mainly about external Si-OH for smaller crystal particle and bigger outside surface area.2. The hydroxyl groups and propylene epoxidation performance of TS-1 catalysts changed significantly with different modification methods. For Na2SO3 modification, the hydroxyl groups of the TS-1 catalysts changed most. Moreover, the propylene epoxidation reaction activity has been improved significantly with Na2SO3,NaHSO3 and TPAOH modified TS-1 catalysts.3. The hydroxyl groups and acidity of TS-1 catalysts has been changed after dielectric barrier discharge plasma treatment, whilethe skeleton structure unaltered.