Direct gas-phase photocatalytic epoxidation of propylene with molecular oxygen by photocatalysts

Abstract

The photocatalytic epoxidation of propylene by molecular oxygen is one of the best methods to produce propylene oxide (PO) from the environmental viewpoints. The key is using photo-energy to achieve high PO selectivity and yield at mild conditions. A series of photocatalysts including SiO2, TiO2, V-Ti/MCM-41, V2O5/SiO2, Au/TiO2 and TS-1, were used to evaluate their performance in the photo-epoxidation. The photocatalytic epoxidation of propylene was carried out in the gas mixture of C3H6:O-2:N-2 = 1:1:18 at atmospheric pressure. In addition to PO, other products, such as propionaldehyde, acetone, acetaldehyde, ethanol and methanol, were detected. The results indicated that the most favorable photocatalysts for photocatalytic epoxidation were silicates supported group. The highest PO formation rate of 114 mu mol g cat(-1) h(-1) with selectivity of 47% was obtained over V-Ti/MCM-41 on stream after 4 h at 50 degrees C and atmospheric pressure under UVA irradiation of 0.2 mW/cm(2). In addition, the selectivity of products was very stable on stream. A possible reaction mechanism was proposed based on the knowledge of species presented during the photocatalytic reaction. (C) 2011 Elsevier B.V. All rights reserved.