Iridium Single-Atom Catalyst Performing a Quasi-homogeneous Hydrogenation Transformation of CO2 to Formate

Heterogeneous single-atom catalysts (SACs) with atomically dispersed active metal centers represent an intermediary between heterogeneous and homogeneous catalysis. In this work, a porous organic polymer with aminopyridine functionalities was designed to fabricate a stable, atomically dispersed Ir catalyst. This Ir-based SAC exhibits excellent catalytic activity during the liquid-phase hydrogenation of CO2 to formate. The associated turnover number is as high as 25,135, representing the best performance yet for a heterogeneous conversion of CO2 to formate. Spectral characterization and density functional theory modeling demonstrate that the chemical structure of the Ir single-atom active site is analogous to that of a homogeneous mononuclear Ir pincer complex catalyst. As a result, a catalytic mechanism similar to that over a homogeneous Ir catalyst occurs during CO2 hydrogenation with this quasi-homogeneous Ir-based SAC. This work suggests a promising basis for the design of efficient SACs for the once-dominant homogeneous catalytic processes.