Atomic-scale study of the Rh/$\gamma $-alumina catalytic system

Prerequisite to the non-empirical design and refinement of improved heterogeneous catalysts is the identification of the atomic-scale structure and properties of the catalytically active sites. We report an investigation of the Rh/$\gamma $-alumina system, which 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 Rh-containing ``rafts'' on the (100) exposure. This finding is surprising given that the preferred exposure of $\gamma $-alumina is (110). First-principles density functional studies and image simulations suggest that these Rh-containing structures consist of the high-pressure rhodium sesquioxide (II) phase growing on the surface. The high pressure phase of rhodium sesquioxide and $\gamma $-alumina (100) exposure yield improved interface match over the regular rhodium sesquioxide phase and $\gamma $-alumina (110) exposure.