Iridium Single-Atom Catalyst Laboring a Quasi-Homogeneous Hydrogenation Transformation of CO2 to Formate

Abstract

Heterogeneous single atom catalysts (SACs) with atomically-dispersed active metal centres represent an intermediary between heterogeneous and homogeneous catalysis. However, the design of SACs for homogeneous processes remains challenging. In the present work, a porous organic polymer with aminopyridine functionalities was designed so as 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 reaction. Spectral characterization and density functional theory modelling demonstrate that the architecture 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.