Bifunctional MOF heterogeneous catalysts based on the synergy of dual functional sites for efficient conversion of CO₂under mild and co-catalyst free conditions

Abstract

Two ionic liquids functionalized CUSs-containing MOF heterogeneous catalysts, MIL-101-N(n-Bu) 3 Br and MIL-101-P(n-Bu) 3 Br, have been prepared by post-synthesis modification method. Due to their synergetic role of Lewis acid sites and Br¯ in ion liquid sites, MIL-101-N(n-Bu) 3 Br and MIL-101-P(n-Bu) 3 Br exhibit high catalyst activity for the cycloaddition of CO 2 and epoxide under mild and co-catalyst free conditions.We reported here a strategy by combining CUSs (CUSs = coordinatively unsaturated metal sites) based MOF with ion liquids (ILs) functional sites to form bifunctional heterogeneous catalysts with extra high activity for CO2 fixation. Based on this strategy, two quaternary ammonium salt and quaternary phosphorus salt ionic liquids functionalized CUSs-containing MOF heterogeneous catalysts, MIL-101-N(n-Bu)3Br and MIL-101-P(n-Bu)3Br, have been prepared for the first time by postsynthesis modification method. Due to their synergetic role of dual functional sites including Lewis acid sites in MOF framwork and Br¯ ion in IL functional sites, MIL-101-N(n-Bu)3Br and MIL-101-P(n-Bu)3Br exhibit high catalyst activity for the cycloaddition of CO2 and epoxide under mild and co-catalyst free conditions, which singnificantly outperforms other benchmark MOF catalysts. Moreover, such bifunctional catalysts can be easily recovered and recycled several times without leaching and loss of activity. Our work thus paves a way for the development of IL functionalized MOFs as heterogeneous catalysts for CO2 fixation.

Ionic Polymer Microspheres Bearing a CoIII–Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides

“…The TON was approximately 300–500 moles of product per mole of catalyst based on Co. It is noteworthy that the relatively bulkier epoxides usually displayed low catalytic activities because of steric hindrance and limited diffusion that may limit interaction between the substrates and the active sites, which is akin to the reported “apparent” size‐selective catalysis in porous heterogeneous systems . In this work, SO, which bears an aromatic ring substituent, showed nearly the same activity as PO and ECH in the reaction with CO 2 catalyzed by TBB‐Bpy@Salen‐Co to give cyclic carbonates (Table , entry 4; cf.…”

“…Indeed, the ability of TBB‐Bpy@Salen‐Co to chemically convert CO 2 into a cyclic carbonate product with high efficiency under such mild conditions (60–80 °C, 0.2 MPa CO 2 , no solvent, no additives) is advantageous versus existing homogeneous and heterogeneous catalysts based on halogen ILs, MOFs, and metal–salen complexes (Table S2, entries 1–24, in the Supporting Information). The catalytic performance of TBB‐Bpy@Salen‐Co was also comparable with other bifunctional solid catalysts, which require high‐pressure and high‐temperature reaction conditions to achieve high efficiency (Table S2, entries 25–32, in the Supporting Information).…”

Recent advances in the synthesis and applications of metal organic frameworks doped with ionic liquids for CO 2 adsorption

“…Ma and co-workers [139] reported a strategy to construct bifunctional MOF heterogeneous catalysts by combining CUS-based MOF with IL functional sites. MIL-101-N(n-Bu) 3 Br and MIL-101-P(n-Bu) 3 Br, both of which contain CUS as Lewis acid centers were functionalized with N(n-Bu) 3 or P(n-Bu) 3 .…”

“…The product was separated by filtration, washed with solvents and dried. MIL-101-N(n-Bu) 3 Br and MIL-101-P(n-Bu) 3 Br exhibited high catalytic activity for the cycloaddition of CO 2 and epoxide under mild and co-catalyst free conditions, due to the synergetic role of dual functional sites including Lewis acid sites in the MOF framework and Br -ions in the IL functional sites [139].…”

Rational Construction of an Exceptionally Stable MOF Catalyst with Metal‐Adeninate Vertices toward CO2 Cycloaddition under Mild and Cocatalyst‐Free Conditions

“…However, cocatalysts are required in most cases, which results in extra waste and environmental pollution . To date, some strategies have been explored for the introduction of cocatalyst into MOFs by guest capture, postmodified skeleton and functionalization of organic ligands . For example, a flexible ionic polymer can be inserted into a MOF host, which will efficiently fixate CO 2 with epoxides to afford cyclic carbonates under mild and cocatalyst‐free conditions .…”