Insights into halogen-free heterogeneous CO2 cycloaddition over M-MgO catalysts using DFT calculations and microkinetic simulations: roles of metal doping and acid-base sites

To solve halogen residues in the product of industrial CO₂ cycloaddition homogeneous systems, developing efficient halogen-free heterogeneous catalysts is an effective strategy to replace homogeneous systems. This study designed a series of M−MgO catalysts to investigate the mechanism of CO₂ cycloaddition with ethylene oxide (EO). The results show that the type of doped metal M affects acid-base properties of M−MgO catalysts, thereby affecting reaction path and catalytic performance. CO₂ adsorbed in the form of carboxylate and mixed coordination can act as pseudo halogen species to promote EO ring-opening; the doped metal M can also act as pseudo halogen active center to promote EO ring-opening. Two reactivity descriptors are proposed to screen out high activity Ga-MgO catalyst. The reaction rate of CO₂ cycloaddition could be accelerated by enhancing the stability of transition state formed by Int2B-b ring-closing or weakening the adsorption of oxygen anion intermediate formed by EO ring-opening.