Br-doped Ga2O3/MCM-41 catalyzed synthesis of propylene carbonate from carbon dioxide and propylene oxide†

Ga₂O₃/MCM-41-x (x = 0.4, 0.5, 0.6) heterogeneous catalysts, each with varying levels of Br doping, were synthesized using mesoporous molecular sieves (MCM-41) as a carrier and employed in the synthesis of propylene carbonate (PC) from propylene oxide (PO) and carbon dioxide (CO₂). The reaction was conducted under solvent-free and additive-free conditions. Various techniques were utilized to characterize the catalysts’ chemical composition, morphology, and structure. The effects of varied reaction conditions on PO conversion and PC selectivity using Ga₂O₃/MCM-41-0.5 catalysts were investigated. Under the reaction conditions of 120 °C, 3.5 MPa, 10 h and catalyst dosage of 2.6 wt%, the PO conversion and PC selectivity reached 99.7% and 99.1%, respectively. The catalytic impact correlates strongly with the doping amounts of Ga₂O₃ and Br, primarily due to the interaction of Ga₂O₃ with the surface of MCM-41, leading to the generation of more basic sites and, consequently, a greater abundance of alkali centers. As a nucleophilic reagent, Br functions synergistically with Ga₂O₃/MCM-41, augmenting the ring-opening rate of PO and improving the activation ability of CO₂. The stability of the catalyst underwent evaluation, revealing a slight decrease in activity after repeated use. The reaction mechanism underlying PC synthesis catalyzed by Ga₂O₃/MCM-41-0.5 was speculated.