Metal-Containing Ionic Liquids as Synergistic Catalysts for the Cycloaddition of CO₂: A Density Functional Theory and Response Surface Methodology Corroborated Study

Abstract

Metal-containing ionic liquids possessing bifunctional moieties were identified as efficient catalysts for the synthesis of propylene carbonate (PC) from CO2 and propylene oxide under moderate and solvent free conditions. Density functional theory calculations were performed to rationalize the difference in catalytic activities of the metal-containing ionic liquid catalysts (MeIm)2MCl2, where M was Fe, Cu, or Zn. (MeIm)2ZnCl2 was the most efficient catalyst for the chemical fixation of carbon dioxide in terms of efficiency and environmental benignity. Process optimization using response surface methodology was performed, and the interactions between the operational variables were elucidated. The optimum reaction conditions for maximum PC yield were 4.6 h, 124 °C, and 9 bar which were obtained by a Box–Behnken design with the minimum number of reaction tests. Under the optimum reaction conditions, the predicted and validated yields of PC were 98.37 and 97.91 ± 0.02%, respectively.