CO2 adsorption and catalytic application of Co-MOF-74 synthesized by microwave heating

High-quality Co-MOF-74 crystals were successfully synthesized in 1 h by microwave heating (Co-MOF-74(M)). The XRD pattern and textural properties of Co-MOF-74(M) including the BET surface area (1314 m2 g−1) were virtually identical to those of a sample synthesized in 24 h by the solvothermal method (Co-MOF-74(S), 1327 m2 g−1). Average particle size of the former (ca. 50 μm long and 8 μm wide) was, however, significantly smaller than that of the latter (ca. 300 μm long and 70 μm wide). The H2O adsorption capacities of the crystals at 25 °C were 466 and 605 mg g−1 for Co-MOF-74(M) and Co-MOF-74(S), respectively. The adsorption isotherms of Co-MOF-74(M) for CO2 and N2 showed a high CO2 adsorption capacity (288 mg g−1) and excellent selectivity over N2 (>25:1) at 25 °C. Eight consecutive adsorption–desorption cycles established that there was no deterioration in the adsorption capacity, which showed reversible adsorbent regeneration at 100 °C under He flow for a total duration of 1100 min. Co-MOF-74(M) also demonstrated excellent catalytic performance in cycloaddition of CO2 to styrene oxide under relatively mild reaction conditions (2.0 MPa, 100 °C) with close to 100% selectivity to carbonate confirmed by GC–MS, 1H NMR, and FT-IR. Styrene oxide conversion increased with CO2 pressure and reaction temperature. No appreciable effect of catalyst particle size was detected, and Co-MOF-74(M) could be reused 3 times without loss of catalytic activity and with no structural deterioration.