Synergetic photo-epoxidation of propylene over VTi/MCM-41 mesoporous photocatalysts

• VTi/MCM-41 photocatalysts show synergetic activity on photocatalytic epoxidation.
• Both tetrahedrally coordinated V5+- and Ti4+-modified MCM-41 are active species.
• A mechanism of photo-epoxidation for a synergetic effect is proposed.

The photo-epoxidation of propylene has gained preference among many alternative processes because the current processes for propylene oxide (PO) production are neither economical nor environmentally sustainable. We synthesized various single and binary metal oxides (Ti and V) constructed within the MCM-41 framework and demonstrated their favorable efficiency for the photo-epoxidation of propylene. The results indicated that highly dispersed tetrahedral coordination states played a role in photo-epoxidation. The maximum PO formation rate was 634 ± 17 (μmol g−1 h−1) on V0.2Ti0.3/MCM-41 under UV-light irradiation of 0.3 mW cm−2 at 323 K. The Delplot method revealed two pathways to produce PO. One is indirectly from propionaldehyde via either V or Ti oxides, and the other is directly from a C3H6 reactant via Ti oxides. This paper clearly illustrates how V and Ti oxides affect the photo-epoxidation pathways. Furthermore, a possible photo-epoxidation mechanism via the metal oxide active site is proposed to elucidate the synergetic photoactivity.

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