Supported iridium cluster catalysts for propene hydrogenation: Identification by X-ray absorption spectra measured during catalysis

Supported metal carbonyl clusters, [Ir-4(CO)(12)]/gamma-Al2O3, [Ir-6(CO)(15 )](2-)/gamma Al2O3, and [HIr4(CO)(11)](-)/MgO, were treated in He to prepar e supported metal clusters modeled as Ir-4/gamma-Al2O3, Ir-6/gamma-Al2O3, a nd Ir-4/MgO. The samples were characterized by infrared and extended X-ray absorption fine structure (EXAFS) spectroscopy, with the EXAFS data obtaine d for samples at liquid nitrogen temperature under vacuum and at 298 K in a flow-through cell in the presence of a) N-2, b) H-2, c) propene, and d) H- 2+propene mixtures; the mixtures underwent catalytic hydrogenation during t he measurements. The results indicate that the cluster frames were essentia lly unchanged under the various conditions. The Ir-4 and Ir-6 clusters are identified as the catalytically active species.