CO2 cycloaddition of styrene oxide over MOF catalysts

Metal organic framework (MOF) structures of UIO-66, UIO-66-NH2, Mg-MOF-74, MIL-101, CuBTC, ZIF-8, IRMOF-3, and MOF-5 having different acid/base properties were prepared and tested for their catalytic activity in the CO2 cycloaddition to styrene epoxide using a high-pressure batch reactor. The high crystallinity and excellent textural properties of the prepared MOF materials were confirmed by XRD and the N2 adsorption–desorption isotherms at 77 K. Their catalytic cycloaddition activities were found to be well correlated with the Lewis acid/base distributions of the materials examined by NH3- and CO2-TPD, respectively, such that the concurrent presence of Lewis acid and base sites were desirable for high catalytic activity. For a given catalyst weight, UIO-66-NH2 showed the best catalytic performance among the MOF samples tested with close to 100% selectivity to carbonate in chlorobenzene under relatively mild reaction conditions (2.0 MPa, 373 K). UIO-66-NH2 could be reused 3 times without losing catalytic activity in a truly heterogeneous mode without structural deterioration, and it also exhibited excellent cycloaddition activities for different epoxide substrates as well.