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The efforts to achieve sustainable chemical conversion and efficient CO2utilization are critical to addressing climate change and environmental sustainability, and therefore the development of effective CO2conversion catalysts is crucial. In this study, novel acid-base bifunctional catalysts, MIL-101-SO3H@Atz and MIL-101-SO3H@DAtz, were successfully synthesized using MIL-101-SO3H as an acid support material through post-synthetic modification with 3-amino-1,2,4-triazole (Atz) and 3,5-diamino-1,2,4-triazole (DAtz) for CO2conversion reaction. The incorporation of the amine species into MIL-101-SO3H created unique synergistic effects with dual acid-base catalytic sites, facilitating the efficient conversion of CO2and epoxides into cyclic carbonates. Among the catalysts, MIL-101- SO3H@DAtz demonstrated superior catalytic performance with achieving 100% epichlorohydrin (ECH) conversion with over 99% selectivity to cyclic carbonate with high selectivity of > 99% under the ambient condition of 1 bar CO2without any co-catalyst or solvent. The elucidated CO2cycloaddition reaction mechanism highlights the synergistic effects of acid-base functionalities and CO2-philic Lewis bases as well as hydrogen bonding donor groups, providing valuable insights into the factors contributing to superior catalytic performance. The simulated flue gas (15% CO2/85% N2, v/v) was also conducted using MIL-101-SO3H@DAtz catalyst. Additionally, the MIL-101-SO3H@DAtz catalyst exhibited remarkably robust structural stability and recyclability, maintaining its activity over multiple cycles.

This work demonstrates the development of a hierarchical mesoporous hybrid ZIF-8 with 1,2,4-triazole (T), ZIF-8T, as a heterogeneous catalyst for CO2cycloaddition to epoxides under a solvent- and cocatalyst-free conditions at ambient pressure. The hybrid ZIF-8T catalyst was prepared via a facile one-pot synthesis method using a mixed-ligand of 2-methyl imidazole (2-Mim) and T. The contents of the introduced T ligand in ZIF-8T were controlled by adjusting a molar ratio of T: 2-Mim ligand. Interestingly, the ZIF-8T with 84.9% of T contents showed a hierarchical hollow mesopore properties and it exhibited excellent catalytic performance with 100% conversion of epichlorohydrin with high selectivity (>99%) under mild conditions (80 °C, 1 bar CO2). In addition, ZIF-8T showed high catalytic activity toward various epoxide substrates. This significant activity of ZIF-8T was attributed to the synergistic effect of the abundance of Lewis acid/base sites derived from unsaturated Zn node and N species in T and 2-Mim ligand, along with the inherent properties of hierarchical mesoporosity. Various reaction parameters, including the effect of the reaction temperature, time, and catalyst loading, were investigated to optimize the reaction condition. Additionally, reaction kinetics and the reusability test of the ZIF-8T catalyst were conducted. Based on the results obtained, a plausible reaction mechanism for CO2–epoxide cycloaddition catalyzed by the ZIF-8T catalyst was also predicted.