Evidence of high-pressure rhodium sesquioxide in the rhodium/γ-alumina catalytic system

We report an investigation of Rh-containing nanostructures dispersed on gamma-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 gamma-alumina. This finding is intriguing given that the preferred surface exposure of gamma-alumina is (110). Here we present first-principles density functional studies and simulated Z-STEM imaging suggesting that these Rh-containing structures consist of the high-pressure rhodium sesquioxide (II) phase growing on the surface.