Tailoring morphology of MgO catalyst for the enhanced coupling reaction of CO2 and glycerol to glycerol carbonate

Developing efficient halogen-free catalysts is still a significant challenge for adsorption and activation of CO2 and further preparing glycerol carbonate. Herein, we successfully developed heterogeneous MgO catalyst via morphology-oriented regulation to catalyze the coupling reaction of glycerol and CO2. Specifically, cubic MgO displays more low-coordinated O2– originated from the unique atomic arrangement of (1 1 1) facet, resulting in abundant strong basic sites and surface oxygen vacancies. These strong basic sites promote the adsorption of CO2 to form thermodynamically stable monodentate carbonates near the oxygen vacancies. In addition, nearby surface oxygen vacancies could further enhance the transfer of electrons into the anti-bonding orbitals of CO2 molecules. The synergistic catalytic effect between the strong basic sites and the surface oxygen vacancies significantly facilitates the cycloaddition reaction (the most critical step in the coupling reaction). Therefore, under the optimal reaction conditions (140 °C, 2 MPa CO2, and 4 h), the MgO-C catalyst showed 83 % glycerol conversion and 44 % glycerol carbonate selectivity.