New penta- and hexa-coordinated titanium sites in titanium silicalite-1 catalyst for propylene epoxidation

Creating and identifying catalytically active titanium sites is vital to further enhance performance of titaniumcontaining zeolites, particularly for environmentally friendly titanium silicalite-1 catalyst (TS-1). Herein, we prepared a typical TS-1 with two new Ti-sites including the penta-coordinated Ti(OH)2(OSi)3 and hexacoordinated Ti(OH)4(OSi)2. They are identified by UV resonance Raman spectroscopy and their coordination structures delineated by density functional theory calculations. Evaluated by propylene epoxidation to propylene oxide, Ti(OH)4(OSi)2 is more active than Ti(OH)2(OSi)3. Furthermore, Ti(OH)4(OSi)2 delivers the catalytic activity about 8.7 times the activity of known tetra-coordinated framework Ti(OSi)4 sites. Thus, Ti(OH)4(OSi)2 is found to be highly active in this reaction.

Automated summary

In this study, we identified two new titanium sites in the environmentally friendly titanium-containing zeolite catalyst, TS-1. These sites, namely penta-coordinated Ti(OH)2(OSi)3 and hexacoordinated Ti(OH)4(OSi)2, were characterized using UV resonance Raman spectroscopy and density functional theory calculations. The hexacoordinated Ti(OH)4(OSi)2 site exhibited higher catalytic activity compared to the penta-coordinated Ti(OH)2(OSi)3. Additionally, the catalytic activity of Ti(OH)4(OSi)2 was found to be approximately 8.7 times higher than that of the known tetra-coordinated framework Ti(OSi)4 sites, indicating its high activity in propylene epoxidation to propylene oxide.