Role of Ga in promoting epoxidation of cis-cyclooctene over Ga-WO_x/SBA-15

This article investigates the promoting effect of gallium (Ga) on the activity of Ga-WO_x/SBA-15 catalyst for cis-cyclooctene epoxidation with H₂O₂. The optimal catalyst of 0.3Ga-WO_x/SBA-15 offered a turnover frequency (TOF) of 112 h^–1, which was nearly two times than that of WO_x/SBA-15 (57 h^–1). The low apparent reaction activation energy for 0.3Ga-WO_x/SBA-15 (49.6 kJ/mol vs 64.0 kJ/mol for WO_x/SBA-15) was also in line with its superior performance. Kinetic analysis demonstrated stronger adsorption of H₂O₂ on 0.3Ga-WO_x/SBA-15 surface, facilitating the H₂O₂ activation. Based on the characterizations and catalytic performance, the improvement of Ga was attributed to the increase of Lewis acid sites and the enhancement of electrophilicity. Furthermore, the metal hydrogen peroxide (M-OOH) was identified as the primary intermediate.