The fixation of carbon dioxide with epoxides catalyzed by cation-exchanged metal-organic framework

Abstract

Metal-organic frameworks (MOFs) possess high porosity and specific surface area and have been extensively applied in the capture and separation of CO2 from flue gas or natural gas. UTSA-16 is the second highest porous MOF for CO2 capture, which is attributed to its microporous structure with anatase type and the fact that the K+ species located in the channel can interact with CO2 molecule. Herein, a sequence of alkali metal cation-exchanged UTSA-16 (hereinafter denoted as M-UTSA-16, M = Li, Na, K, Rb, Cs) were prepared and evaluated for CO2 capture. The CO2 adsorption isotherms of M-UTSA-16 obtained at 273K and 298K showed that the adsorption capacity for CO2 decreased in the sequence of K+>Na+>Li+>Rb+>Cs+. The series of M-UTSA-16 were used as the catalyst for the transformation of CO2 and epoxide to cyclic carbonate in the absence of co-catalyst. Li-UTSA-16 exhibited the highest efficiency of catalytic activity compared with other M-UTSA-16. The result was inconsistent with the sequence of CO2 adsorption capacity. The further systematic investigation showed that the decreasing order of catalytic activities of M-UTSA-16 was in agreement with the sequence of increasing radius of the exchanged cations as well as the heat of adsorption for CO2 at lower pressure region.