Secondary-Synthesis Of Titanium Silicalite Using Natural Mordenite

Titanium silicalite-1 (TS-1) is a titanium-containing zeolite with the MFI structure that was first synthesized in 1980's. The system of TS-1 and H₂O₂ exhibits excellent catalytic and oxidative properties under mild conditions, besides, the above process has overcome the shortcomings of serious pollution and unsafe factors of traditional oxidative technologies, and it has provided new pathway for the green chemical engineering and environmentally friendly processes.Therefore TS-1 has received more and more attention of the researchers at home and abroad. In the past twenty years, many improvements have been made, which include decreasing the synthetic costs, enhancing the preparing repetition, decreasing the amount of anatase TiO₂ and expanding its industrial applications.In the field of synthesis, the hydrothermal synthesis, especially the low cost system, developed fast in the past decades. Compared to the classic hydrothermal method, secondary synthesis or post synthesis, including the liquid-solid and gas-solid preparation way can be used to study the synthesis of titanium silicalite from more extensive field, based on the synthesized precursor. Besides, the operating conditions of the secondary synthesis reaction are not vigor and the raw materials are cheaper. So, the study of this technique has become one of the most important directions in the field of the titanium silicalite. However, the cost is still high, because in the synthesis process of precursor, not only the use of template is necessary, but also the synthesis conditions are harsh.Natural zeolite is very important mineral resources in the world, compared with synthesized zeolite, it is abundant in deposits and much cheaper, the application has aroused wide attention. But because of its low purity and simple framework composition, it's currently excluded from almost all of the important large-scale industrial application, so riching the simple zeolite framework composition of is the key factor to change the situation that natural zeolite being mainly used as low-value products, such as cement or building materials, and to make them into important industrial catalyst and environmental protection functional materials.In this paper, we chose the high quality Jinyun mordenite in Zhejiang province as the raw material to prepare titanium-containing mordenites using the secondary synthesis method, and studied their catalytic property of epoxidation of styrene. Samples were characterized by X-ray diffraction (XRD), Fourier-transformed infrared (FT-IR), UV-Vis spectroscopy, diffuse reflectance and X-ray photoelectron spectroscopy (XPS) as well as inductive coupled plasma-atomic emission spectroscopy (ICP-AES). The result showed the method of combing dealumination and liquid-solid/gas-solid phase isomorphous replacement could incorporate titanium into the framework of mordenites, making natural mordenite into titanosilicate with good performance in the catalytical oxidation.of styrene.There is close relationship between the properties of mordenite precursor and the preparation of titanosilicate with secondary synthesis method. In this paper, effect of different acid treatment of the physicochemical properties of mordenite was firstly studied, after that, effect of different physicochemical properties of mordenite precursors on preparation of titanosilicate with secondary synthesis method was further investigated.Preparation conditions was optimized in the process, and a new plot of the liquid-solid method, "multi-step dealumination and titanation", was produced for the first time to control effectively the titanium content incorporated into the framework, without the existence of extraframework TiO_x as well.Aluminium content in mordenite precursor and reaction temperature are key factors in the incorporation process of Ti atom into mordenite framework with gas-solid reation. Increasement of titanium content and decreasement of extraframework TiO_x species could be achieved through enhancing dealumination gradually and adjusting to suitable reaction temperature and treatment temperature...