CO₂ Cycloaddition under Ambient Conditions over Cu-Fe Bimetallic Metal-Organic Frameworks

Carbon dioxide cycloaddition into fine chemicals is prospective technology to solve energy crisis and environmental issues. However, high temperature and pressure are usually required in the conventional cycloaddition reactions of CO₂ with epoxides. Moreover, metal active sites play a vital role in the CO₂ cycloaddition, but it is still unclear. Herein, we select the isostructural MOF-919-Cu-Fe and MOF-919-Cu-Al as models to promote the performance and clarify the effects of metal type on the CO₂ cycloaddition. The MOF-919-Cu-Fe with exposed Fe and Cu Lewis acid sites reaches the CO₂ cycloaddition with over 99.9% conversion and over 99.9% selectivity at room temperature and a 1 bar CO₂ atmosphere, 3.0- and 52.6-fold higher than those of the MOF-919-Cu-Al with Al and Cu sites (33.8%) and the 1H-pyrazole-4-carboxylic acid, Fe, and Cu mixed system (1.9%), respectively. The proposed mechanism demonstrated that the exposed Fe³⁺ sites facilitate the ring opening of epoxide and CO₂ activation to boost the CO₂ cycloaddition reaction. This work provides a new insight to tune the catalytic sites of MOFs to achieve high performance for CO₂ fixation.