Gold-Iridium Catalyst Particles Remain Stable On Titania Support

Metal nanoparticles supported on solids are widely used as catalysts to drive petroleum refining, automobile emissions cleanup, and other processes. But prolonged exposure to high temperature causes these particles to wander across the support and coalesce, or sinter, with other catalyst particles. That process buries the particles’ active sites, causing the catalyst to become ineffective. Gold nanoparticles are especially prone to this form of deactivation and therefore the metal is not typically used, despite its exceptional activity at low temperature. Thanks to a study led by Volkan Ortalan and Jeffrey Greeley of Purdue University, researchers may want to reconsider gold’s catalytic potential. The team found that alloying gold with a small amount of iridium via sequential deposition of the metals on TiO₂ produced gold-iridium nanoparticles that strongly resist sintering even at 500 °C (Nano Lett. 2015, DOI: 10.1021/acs.nanolett.5b03585). An analysis involving electron tomography and quantum calculations revealed that iridium preferentially collects at the interface between the particles and TiO₂. That arrangement increases the particles’ adhesion to TiO₂ and reduces the thermodynamic driving force to sinter relative to pure gold nanoparticles.