Fig. 4. (a) Proposed structure of the Ti(OH2)(OSi)3(OSiOH)2 by DFT. The grey ball represents the Ti atom, while yellow stands for Si, red for O, and white for H. (b) Reaction pathways in the TS-1/MeOH/H2O2-catalyzed propylene epoxidation. (c) H2O2 conversion, PO yield, and PO selectivity, (d) H2O2 conversion at different reaction times and (e) H2O2 conversion of the recycle test over different TS-1 zeolites. The samples were calcined at 550 °C for 6 h after four cycle.
