Hollow core-shell structured TS-1@S-1 as an efficient catalyst for alkene epoxidation.

Hollow core-shell structured TS-1@S-1 zeolite (HCS-TS) was prepared successfully for the first time, which exhibited excellent activity in the epoxidation of alkenes. Combining TEM, UV-vis, UV-Raman, pyridine-IR, solid-state MAS NMR, XPS and so on characterization, the improvement in the catalytic performance of hollow core-shell structured TS-1@S-1 zeolite was credited to the newly formed superior active sites: defective Ti(OSi)(OH) species in HCS-TS and six-coordinated titanium active species in uncalcined HCS-TS (HCS-TS). Interestingly, these two different titanium active species in the samples could be constructed through calcination or not in the same synthesis process. A possible formation mechanism was investigated in detail; it indicated that the hollowing treatment of TS-1 in the first step was conducive to the construction of the new superior active sites in the samples, and there was a synergistic effect on the formation of these active sites between TPAOH and TEOS in the second step of the synthesis process. This strategy is feasible to enhance the catalytic performance of TS-1, and is suitable for the synthesis of TS-1 on an industrial scale.