Influence of co-feeds additive on the photo-epoxidation of propylene over V–Ti/MCM-41 photocatalyst

• The presence of H2O, or H2 co-feed changes the reaction activity and the catalyst stability during photo-epoxidation.
• A small amount of H2O leads to enhanced activity and stability, but excess H2O will cause surface site blocking.
• The catalyst stability increases when acetaldehyde (AA) is enhanced, suggesting that AA accumulation lead to deactivation.

In this work, the effects of co-feed species, namely, H2O or H2, on the photocatalytic epoxidation of propylene over V–Ti/MCM-41 are examined. A promoting effect on the C3H6 consumption rate is found under 0.6 kPa H2O co-feed when the PO (propylene oxide) formation rate is not proportionally promoted, resulting a slightly decreased PO selectivity. With increasing H2O concentration, the reaction activity decreases and this can be attributed to surface site blocking by excess H2O. The presence of H2O also increases the stability of photocatalyst during reaction. Similar observation of the enhanced C3H6 consumption rate and the improved stability is found when 5.6 kPa H2 is used as co-feed. We found that the catalyst stability is improved when the AA (acetaldehyde) is increased. This suggests that AA accumulation on the catalyst surface may lead to surface fouling and the observed deactivation. The presence of H2O or H2 co-feed, which can lead to hydroxyl radical (OH
• ), may impose a shift in the production formation of photocatalytic reaction.

Figure optionsDownload high-quality image (199 K)Download as PowerPoint slide