Selective propylene epoxidation in liquid phase using highly dispersed Nb catalysts incorporated in mesoporous silicates

Selective propylene epoxidation to propylene oxide (PO) with hydrogen peroxide (H₂O₂) was carried out in a catalytic semi-batch reactor. High propylene epoxidation activity (44 h^-1) was observed over Nb based mesoporous silicate materials Nb-TUD-1 under mild operating conditions. The physical and chemical properties of the Nb based silicates characterized using BET, FTIR, TPD, TEM and UV-Vis revealed that the site isolation and surface acidity are crucial for PO production. Catalyst synthesis methods were investigated for their effects on PO productivity, PO selectivity and H₂O₂ utilization efficiency. It is found that Nb-TUD-1 material synthesized by the sol-gel method is more active and selective than impregnated materials for liquid phase propylene epoxidation. Surface characterization confirms that thus synthesized Nb-TUD-1 catalysts have more Lewis acidity and less Bronsted acidity compared to the catalysts by impregnation.