Electronic Structure of Atomically Dispersed Supported\nIridium Catalyst Controls Iridium Aggregation

Abstract

Supported\niridium complexes, Ir­(C₂H₄)₂/support,\nwere characterized by X-ray absorption spectroscopy\nduring a temperature ramp to 120 °C in flowing H₂.\nIridium in complexes bonded to weak and moderate electron-donor supports,\nSiO₂ and γ-Al₂O₃, underwent\naggregation, forming nanoparticles and clusters, respectively. When\nthe support was a strong electron-donor (MgO), iridium remained site-isolated.\nDensity functional theory calculations confirm the dependence of iridium–support\nbond strength on the support’s electron-donor character. Coating\nthe SiO₂-supported complexes with 1-<i>n</i>-ethyl-3-methyl-imidazolium\nacetate enhanced electron density on the iridium, hindering its aggregation.\nThese results demonstrate opportunities for stabilizing atomically\ndispersed supported noble metals under reducing conditions by choice\nof support/ionic liquid sheath combinations.