Synergistic Effects of Poly(ionic liquids)@MOF-808 Nanocomposites for Direct Conversion of Carbon Dioxide into Dimethyl Carbonate

The direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO₂) and methanol (CH₃OH) represents one of the most attractive strategies in green chemistry, offering 100% atom economy for CO₂ utilization. However, this reaction faces significant thermodynamic and kinetic challenges, limiting its practical application. To overcome these barriers, the development of highly efficient catalysts capable of effectively activating the CO₂ is essential to achieve industrially viable DMC yields. Herein, a series of poly(ionic liquids) (PILs)@MOF-808 nanocomposites (including poly[AlDBU]Br@MOF-808, poly[AlDBN]Br@MOF-808, and poly[AlTMG]Br@MOF-808) were successfully synthesized via in situ polymerization. These composites integrate Lewis basic N sites, Lewis acidic Zr centers, and nucleophilic Br⁻ within a MOF-808 framework. The nanocomposites were evaluated in a batch autoclave for the direct synthesis of DMC from CO₂ and CH₃OH. Among them, poly[AlDBU]Br@MOF-808 showed the highest DMC yield. Through systematic optimization of the poly[AlDBU]Br loading and reaction parameters (including temperature, CO₂ pressure, and time), a maximum DMC yield of 2.52 mmol·g⁻¹cat was achieved with poly[AlDBU]Br@MOF-808-0.4 at 120 °C under 3 MPa of CO₂ for 5 h. Experimental studies and in situ DRIFTS confirmed the synergistic catalytic effect between MOF-808 and the PILs, highlighting their cooperative role in enhancing CO₂ activation and DMC formation. The catalytic performance of poly[AlDBU]Br@MOF-808-0.4 is competitive compared to previously reported catalysts. The fundamental understanding of the synergistic effects between MOF-808 and PILs offers groundbreaking insights for CO₂ capture and utilization strategies in direct DMC synthesis.