Electronic Structure of Atomically Dispersed Supported Iridium Catalyst Controls Iridium Aggregation

Abstract

Supported iridium complexes, Ir(C2H4)2/support, were characterized by X-ray absorption spectroscopy during a temperature ramp to 120 °C in flowing H2. Iridium in complexes bonded to weak and moderate electron-donor supports, SiO2and ?-Al2O3, underwent aggregation, forming nanoparticles and clusters, respectively. When the support was a strong electron-donor (MgO), iridium remained site-isolated. Density functional theory calculations confirm the dependence of iridium-support bond strength on the support's electron-donor character. Coating the SiO2-supported complexes with 1- n-ethyl-3-methyl-imidazolium acetate enhanced electron density on the iridium, hindering its aggregation. These results demonstrate opportunities for stabilizing atomically dispersed supported noble metals under reducing conditions by choice of support/ionic liquid sheath combinations.