We investigated the interface structure between the Pt nanoparticles and the alumina Support in a Pt/Al2O3 model catalyst reduced in flowing hydrogen gas at different temperatures by cross-sectional atomic-resolution transmission electron microscopy nanodiffraction techniques. An interfacial PtgAl21 alloy with a tetragonal Structure was formed at the Pt-alumina interface during the high-temperature reduction at 1073 K. This alloy phase was not formed when the Pt/Al2O3 model catalyst was reduced at 773 K. The platinum-assisted reduction of the alumina support and the subsequent strong metal-support interaction at the interface may be responsible for the formation of the interfacial alloy phase. (c) 2005 Elsevier Inc. All rights reserved.