Tailoring of Unsaturated Metal Sites in Metal–Organic Frameworks to Promote the Conversion of CO2 into High-Value-Added Products

Abstract

Well-defined metal–organic frameworks (MOFs) provide an attractive platform for catalysis. Understanding the intrinsic structure–activity relationship of MOFs helps guide the design of novel catalysts. In this work, a new three-dimensional (3D) Mn^II(salen)-based MOF (1) with strong adsorption capacity and high selectivity for CO₂ was synthesized. Through sequential demetallization and remetallization, the flexible tailoring of the metal centers was realized to obtain a series of remetallized MOFs (r1^M; M = Mn, Co, Cu, Ni, V). Among them, r1^Co was proved to be the most active catalyst for the cycloaddition of CO₂ and epoxides. Mechanistic studies reveal that r1^Co displays a high CO₂ affinity and Lewis acidity. In addition, kinetic studies suggest that r1^Co has a lower activation energy than the original MOF (1) and demetallized MOF (d1). Remarkably, r1^Co could be reused five times without affecting its catalytic activity.