We report an investigation of Rh-containing nanostructures dispersed on γ-alumina.This system is representative of many common heterogeneous catalysts that consist of transition metals dispersed on a high surface area support.Previous atomic-resolution Z-contrast STEM observations have shown the Rh particles to exist as thin "rafts" on the (100) surface of γ-alumina.This finding is intriguing given that the preferred surface exposure of γ-alumina is (110).Here we present first-principles density functional studies suggesting that these Rh-containing structures consist of the high-pressure rhodium sesquioxide (Ⅱ) phase growing on the surface.