Ionic metal−organic frameworks (MOFs) offer a new platform to design and construct complete heterogeneous bifunctional catalytic systems for the chemical fixation of CO 2 with epoxides. Herein, we developed a series of bifunctional pyridinium ionic MOF heterogeneous catalysts (66Pym-RXs and 67BPym-MeI) by the postsynthetic N-alkylation of noncoordinated pyridine sites in porous MOFs. The synergetic catalytic effect of acidic sites with nucleophilic anions in the ionic MOF significantly enhanced the catalytic activity toward the cycloaddition of CO 2 with epoxides to produce cyclic carbonates under cocatalyst-free and solvent-free mild conditions. The catalytic activity of ionic MOFs is easily tuned by the introduction of different alkyl groups into pyridinium cations and halide ions. The 66Pym-iPrI catalyst displayed the highest catalytic performance in terms of the turnover number value for the synthesis of cyclic carbonates. The proposed alternative method provides the means of developing functional N-heterocyclic groups for the new design of bifunctional ionic MOFs as potential heterogeneous catalysts for CO 2 fixation applications.

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Metal-containing ionic liquids (MIL) are highly active homogeneous catalysts for the chemical fixation of CO2 into epoxides yielding five-membered cyclic carbonates. To obtain sustainability, polymer-supported MIL catalysts were designed to overcome their previously reported inherent poor recoverability. Polymer-supported Zn-containing imidazolium salts, PS-(Im)2ZnX2, possessing bifunctional properties were identified as sustainable catalysts for the activation of CO2 under solvent-free conditions. PS-(Im)2ZnX2 showed good catalytic performance and was readily recoverable and reusable in the subsequent reaction cycles for the cycloaddition of CO2 to propylene oxide. Kinetic studies for the cycloaddition of CO2 to propylene carbonate using batch or semibatch systems were performed to calculate the approximate rate constants, which provide an explanation for the different reaction systems. In addition, process optimization using the response surface methodology was performed, and the interactions between the operational variables were identified. The results demonstrate the advantage of the semibatch system, which allows the completion of the reaction in less time than when using the batch system.