N-Coordinated Ir single atoms anchored on carbon octahedrons for catalytic oxidation of formaldehyde under ambient conditions

Abstract

Molecular oxygen activation over single atoms catalysts (SACs) has been a thorny issue in catalytic oxidation of toxic formaldehyde (HCHO) under ambient conditions. Metal oxide supported SACs are far from satisfactory due to the insufficient oxygen activation and high temperature (>20 °C) for complete oxidation of HCHO. Herein, N-doped carbon was selected as a non-oxide support to stabilize iridium single atoms (Ir₁–N–C), which could deliver high HCHO removal and conversion efficiency (>95%) with high/low concentrations at 20 °C. The specific rate can reach 401.8 mmol g_Ir⁻¹ h⁻¹, superior to that of Ir-based catalysts reported to date. The local structure of Ir–N₄ sites was confirmed by spherical aberration correction electron microscopy and X-ray absorption fine structure. Based on the theory calculations and electron spin resonance results, the strong electronegativity of N atoms in Ir–N₄ active sites enhanced the polarization of Ir atoms, thus forming strong electronic coupling between the Ir 5d orbitals and O₂ 2p orbitals, promoting the dissociation of O₂. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed the main reaction pathways. Dioxymethylene (DOM) and formate species were detected as the intermediates. This work enlightens the great potential of Ir SACs supported on non-oxides in air purification including HCHO.