State of iridium supported on SO4/ZrO2

The Ir/ZrO2 and Ir/SO4/ZrO2 systems were studied by diffuse-reflectance IR spectroscopy using CO as a probe molecule. After reduction of 0.5% Ir/ZrO2 in flowing hydrogen at 200°C, the state of iridium is essentially Ir0, as in the iridium systems supported on amphoteric oxide supports. For Ir/SO4/ZrO2, the stabilization of ionic forms of the metal, the formation of species with a partial positive charge, and an increase in the frequencies of CO adsorbed on Ir0 particles, as compared with systems without sulfur, are found. At a concentration as low as 0.1 wt.%, iridium exists substantially as Ir3+ ions or small Ir⋆+ particles. An increase in the concentration of iridium to 0.5 wt.% leads to the formation of the bulk Irn0 phase, whose fraction increases as the iridium content increases. This phase predominates in the samples with 2.5 wt.% iridium.