Titanium Silicon Molecular Sieve（2）
The synthesis methods of these titanium-silicon molecular sieves are complicated and simple, mainly including direct hydrothermal synthesis method, dry glue method, post-processing atomic implantation method, etc. The physical properties such as UV-visible spectroscopy and infrared spectroscopy show that the Ti+ in the framework of these titanium-silicon molecular sieves are all in a highly dispersed four-coordinate state. However, due to the different synthesis methods and the characteristics of their own channels, the performance of these titanium-silicon molecular sieves in the selective oxidation of hydrocarbons is different.
Ti-Beta molecular sieve contains double twelve-membered ring channels, and the pore size is larger than the ten-membered ring channel of TS1 molecular sieve. It shows advantages in the selective oxidation of macromolecular substrates, but due to its polycrystalline molecular sieve structure, it leads to structural defects. More sites have poor hydrophobicity, which affects its further promotion and application in industry. Ti MWW not only has an open supercaged structure with an internal ten-membered ring but also a bowl-shaped twelve-membered cavity on the surface, which effectively increases the accessibility of the substrate molecules to the active sites. The unique layered structure of Ti-MWW makes it possible to further increase the external surface area and improve its activity in macromolecular epoxidation through post-processing methods such as exfoliation, intercalation, and pillaring. These new titanium-silicon molecular sieves show higher activity and better selectivity than TS1 molecular sieves in the selective oxidation of small molecules and macromolecular olefins. In addition, they have good reusability and become a new generation of titanium-silicon. Molecular Sieve.
With the rise of mesoporous molecular sieves, Ti atoms have also been introduced into mesoporous channels by post-processing grafting to synthesize mesoporous titanium-silicon molecular sieves, such as Ti-MCM-41, TiSBA-15, etc. Amorphous, not only causes Ti+ to be unable to exist in the framework in a four-coordination state, but also makes the titanium-containing mesoporous materials have strong hydrophilicity. As a result, such materials can only be used in macromolecular substrates ( Such as cyclohexene, etc.) selective oxidation reaction shows advantages.
