Synthesis of Propylene Carbonate from Carbon Dioxide through High Activity of Magnesium Oxide

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In this study, hydromagnesite sheets have been prepared under simple hydrothermal process treatment of solution of MgCl₂ and urea. Calcination of the hydromagnesite sheets at 800°C in air for 4 h resulted in porous MgO with polyhedra in the morphology. The high crystalline MgO polyhedra were of side 4–10 µm length and 2–6 µm thickness, and consisted of large number of pores, edges and corners, surface hydroxyl groups and low coordinate O₂⁻ sites which were regarded as active basic sites in heterogeneous base catalysts. The MgO polyhedra can function as a solid base catalyst for the synthesis of propylene carbonate (PC) from CO₂ and propylene oxide (PO). With MgO catalyst calcined at 800°C, the PC yield was 95% and selectivity 99% under mild conditions (1.5 MPa, 10 h). Furthermore, the MgO catalyst can be readily separated and recycled in a test of four cycles.