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

Abstract

Creating and identifying catalytically active titanium sites is vital to further enhance performance of titanium-containing 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 hexa-coordinated 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.