Non-3d metal modulated zinc imidazolate frameworks for CO2 cycloaddition in simulated flue gas under ambient condition

Abstract

Cycloaddition of CO 2 and epoxide into cyclic carbonate is one of the most efficient ways for CO 2 conversion with 100% atom-utilization. Metal–organic frameworks are a kind of potential heterogeneous catalysts, however, high temperature, high pressure, and high-purity CO 2 are still required for the reaction. Here, we report two new Zn(II) imidazolate frameworks incoporating MoO 4 2– or WO 4 2– units, which can catalyse cycloaddition of CO 2 and epichlorohydrin at room temperature and atomospheric pressure, giving 95% yield after 24 h in pure CO 2 and 98% yield after 48 h in simulated flue gas (15% CO 2 + 85% N 2 ), respectively. For comparison, the analogic Zn(II) imidazolate framework MAF-6 without non-3d metal oxide units showed 71% and 33% yields under the same conditions, respectively. The insightful modulation mechanisms of the MoO 4 2– unit in optimizing the electronic structure of Zn(II) centre, facilitating the rate-determined ring opening process, and minimizing the reaction activation energy, were revealed by X-ray photoelectron spectroscopy, temperature programmed desorption and computational calculations. Two new zinc imidazolate frameworks integrated with non-3d metal MoO 4 2− and WO 4 2− units were prepared, which displayed significantly enhanced catalytic activities toward CO 2 cycloaddition reaction under ambient condition, even with simulated flue gas.