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Efficient construction of active TiO6 species in TS-1 zeolite via treatment with amines and ammonium salts for enhanced cyclohexene epoxidation

Kaiwei Wang,Hao Ruan,Fumin Wang,Yi Zhai,Mingshuai Sun,Yan Chen,Jiaxing Zhang,Yihao Wang,Xuyang Zou,Xubin Zhang

The construction of abundant TiO 6 active sites within the zeolite framework is essential for further enhancing the catalytic performance of TS-1 zeolite. Here, we employ a strategy involving treatment with a mixture of amines and ammonium salts to generate abundant TiO 6 species within zeolites synthesized with the assistance of N,N-dimethylformamide (DMF). It was observed that during the post-treatment process, the presence of amines and ammonium salts plays a key role for the formation of highly active TiO 6 species. The incorporation of DMF can significantly enhance the TiO 6 content in the post-treated zeolite, increasing it to 61.5 % compared with 28.5 % in the zeolite synthesized without DMF. The effect of the DMF/SiO 2 ratio in the synthesized gel on the morphology and catalytic performance was also examined. It is noteworthy that the incorporation of DMF influences the microenvironment of the Ti active sites following post-treatment. 1 H MAS NMR analysis reveals that the characteristic peaks corresponding to Ti-OH and isolated Si-OH groups in the DMF-synthesized catalyst are significantly intensified after treatment with amines and ammonium salts. When H 2 O 2 is employed as an oxidant, the optimal catalytic performance achieves a cyclohexene conversion of 51.1 % and a cyclohexene oxide yield of 39.4 %, with a high TOF value of 92.77 h −1 . Notably, the catalyst exhibits a significantly conversion rate of 79.4 % and a yield of 72.7 % using O 2 as the oxidant.