Controlling dual-positively charged pyrazolium ionic liquids for efficient catalytic conversion of CO into carbonates under mild conditions

To address the ongoing rise in carbon dioxide (CO 2 ) emissions, CO 2 utilization presents a promising approach due to its ability to convert CO 2 into valuable industrial products and enable carbon recycling. For this reason, a high-quality catalyst is required to ensure the effective activation and conversion of CO 2 . In this study, a series of dicationic pyrazolium ionic liquids (DPzILs) were first synthesized via a one-step process and employed as catalysts in the cycloaddition reaction of CO 2 and epoxides, yielding cyclic carbonates. Among the synthesized DPzILs, [DMPz-6]I 2 exhibited outstanding catalytic performance on diluted CO 2 from simulated flue gas (60% CO 2 in N 2 ), achieving 94.1% PC yield and 100% selectivity under reaction conditions (100 °C and 10 bar CO 2 pressure) without metal, co-catalyst, or solvent. The study investigated the effects of DPzILs structures, catalyst dosage, CO 2 pressure, reaction temperature, and reaction time on the production of cyclic carbonates. Furthermore, [DMPz-6]I 2 could be efficiently recovered and reused seven times without significant degradation of catalytic activity. It demonstrated significant adaptability to various epoxides. Structure-activity studies indicated that PO activation is synergistically facilitated by the presence of C3/C5 hydrogen from dual-pyrazolium cation rings tethered by alkyl chain lengths and a paired halide anion (I − /Br − /Cl − ) in DPzILs. Finally, the reaction mechanism was investigated using FT-IR, 1 H NMR, and DFT calculations. Novel dicationic pyrazolium ionic liquids were synthesized and utilized as catalysts for the coupling reaction of diluted/pure CO 2 and epoxides to carbonates under mild conditions without metal/solvent.