Introduction of titanium silicon molecular sieve
The discovery of titanium-silicon molecular sieve TS-1 expands the application of molecular sieves from the field of acid catalysis to the field of selective oxidation, creating a new era in the field of liquid-phase selective oxidation. The environmentally friendly characteristics of its catalytic system promote more efficient molecular sieve oxidation. Research and development of catalytic materials.
Although TS1, as the first generation of titanium-silicon molecular sieve, shows good activity in the selective oxidation of small molecular substrates such as the epoxidation of linear olefins and the hydroxylation of phenol, but when the substrate molecules become toluene, cyclic olefins, etc. In the case of equal macromolecules, due to the limitation of the pore size of the double ten-membered ring, it is difficult for the substrate molecules to diffuse into the pores and close to the active site of Ti, resulting in low activity of TS1. In addition, a large number of expensive organic structural templates and organosilicon sources are used in the synthesis process of TS1, which leads to high preparation cost, which affects and restricts its large-scale industrial application to a certain extent [13]. When TS-1 molecular sieve is used in olefin epoxidation reaction, if methanol is used as solvent, it will easily lead to the hydrolysis and ring opening of the target product epoxide, and reduce the selectivity of the reaction. Most of the research and development of new titanium-silicon molecular sieves revolves around overcoming the shortcomings of the first-generation titanium-silicon molecular sieve TS-1. So far, at least 13 kinds of microporous titanium-silicon molecular sieves have been reported (Table 2-1). Most of these titanium-silicon molecular sieves with different crystal structures contain twelve-membered rings or larger pore system, which to a certain extent Alleviate the deficiencies caused by the channel restriction of TS1 molecular sieve[14-23]