The effect of gas environment (H2, O2) on the structural properties of small iridium metal particles supported on gamma-Al2O3 as determined by EXAFS

EXAFS measurements have been carried out on an 0.8 wt% Ir/¿-Al2O3 catalyst after the following treatments : 1) reduction at 773 K, 2) evacuation at 623 K, 3) O2 adsorption at 77 K, 4) subsequent heating to 100 K. The tentative results show that chemisorbed hydrogen influences the structure of the metal particles and their interaction with the support. Oxygen adsorption at 77 K (most probably physisorption) seems to produce the same kind of metal-oxygen bonds as detected for the metal-support interface, when the metal crystallites are under vacuum. Subsequent heating to 100 K resulted in the onset of oxygen chemisorption