CO2 capture and conversion using Mg-MOF-74 prepared by a sonochemical method

Mg-MOF-74 crystals were successfully prepared in 1 h by a sonochemical method (Mg-MOF-74(S)) after triethylamine (TEA) was added as a deprotonating agent. Mg-MOF-74(S) (1640 m(2) g(-1) BET surface area) displayed similar textural properties to those of a high-quality MOF sample synthesized in 24 h by the solvothermal method (Mg-MOF-74(C), 1525 m(2) g(-1)). However, mesopores were formed, probably due to the competitive binding of TEA to Mg2+ ions, and the average particle size of the former (ca. 0.6 mu m) was significantly smaller than that of the latter (ca. 14 mu m). The H2O adsorption capacity was 593 mL g(-1) at 298 K for Mg-MOF-74(S), displaying higher hydrophilicity than Zeolite 13X. The adsorption isotherms of Mg-MOF-74(S) for CO2 showed high adsorption capacity (350 mg g(-1) at 298 K) and high isosteric heats of adsorption for CO2 (42 to 22 kJ mol(-1)). The breakthrough experiment confirmed excellent selectivity to CO2 over N-2 at ambient conditions (saturation capacity of ca. 179 mg g(-1)). Ten consecutive adsorption-desorption cycles at 298 K established no deterioration of the adsorption capacity, which showed reversible adsorbent regeneration at 323 K under helium flow for a total duration of 1400 min. Mg-MOF-74(S) also demonstrated excellent catalytic performance in cycloaddition of CO2 to styrene oxide under relatively mild reaction conditions (2.0 MPa, 373 K) with close to 100% selectivity to carbonate, which was confirmed by GC-MS, H-1-NMR, and FT-IR. Mg-MOF-74(S) could be reused 3 times without losing catalytic activity and with no structural deterioration.