Controlling dual-positively charged pyrazolium ionic liquids for efficient catalytic conversion of CO₂ into carbonates under mild conditions

To address the ongoing rise in carbon dioxide (CO2) emissions, CO2 utilization presents a promising approach due to its ability to convert CO2 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 CO2. 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 CO2 and epoxides, yielding cyclic carbonates. Among the synthesized DPzILs, [DMPz-6]I-2 exhibited outstanding catalytic performance on diluted CO2 from simulated flue gas (60% CO2 in N-2), achieving 94.1% PC yield and 100% selectivity under reaction conditions (100 degrees C and 10 bar CO2 pressure) without metal, co-catalyst, or solvent. The study investigated the effects of DPzILs structures, catalyst dosage, CO2 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, H-1 NMR, and DFT calculations.