Chemisorption properties of platinum and iridium supported on TiO 2Al 2O 3 mixed-oxide carriers: Evidence for strong metal-support interaction formation

Abstract

Fresh Pt and Ir on A1 2O 3 catalysts reduced at 773 K exhibit high H M ratios (1 to 2.5) indicative of highly dispersed metal phases. In contrast, TiO 2-supported Pt and Ir catalysts display low H M ratios (<0.04) following hydrogen reduction at 773 K. The suppressed hydrogen uptakes typically exhibited by TiO 2-based Group VIII metal catalysts result from a strong metal-support interaction (SMSI) and not from a poor metals dispersion. Following reduction at 773 K, the H M ratios displayed by Pt and Ir catalysts supported on TiO 2Al 2O 3 mixed-oxide carriers are intermediate in value between those observed on TiO 2 and Al 2O 3 supports. The extent of H 2 uptake suppression is dependent upon the relative TiO 2 and Group VIII metal concentrations on the Al 2O 3 surface. The magnitude of H 2 uptake suppression (and thus SMSI formation) increases at higher TiO 2/Group VIII metal ratios. Higher reduction temperatures and extended reduction times at a given elevated temperature also enhance SMSI formation. Taken together, these results imply that the generation of reduced Group VIII metal-TiO 2− x species on the Al 2O 3 surface may be responsible for the SMSI effect.