Distribution and Valence State of Ru Species on CeO2 Supports: Support Shape Effect and Its Influence on CO Oxidation

In this work, ruthenium (Ru) catalysts supported on CeO2 nanorods (NR), nanocubes (NC), and nanoctahedra (NO) were comparatively investigated to correlate the shape and exposed surface planes ({100}, {110}, and {111}) of nanoscale CeO2 supports with their low-temperature CO oxidation activity. Within the 5Ru/CeO2-r catalysts with three morphologies after reduction treatment, the Ru supported on CeO2 NR exhibited enhanced low-temperature (<100 °C) hydrogen consumption and superior room-temperature CO oxidation activity (∼9% CO conversion). Both X-ray photoelectron spectroscopy and X-ray absorption spectroscopy measurements revealed that Run+ homogeneously predominates the 5Ru/CeO2NR-r, which is very different from partial metallic Ru0 supported on CeO2 NC and NO, indicating the strong metal–support interaction formation between Ru and CeO2 NR by Ru ions diffusing into CeO2 surface lattice or forming Ru–O–Ce bonds at the interface. The enriched surface defects on the exposed {111} planes of CeO2 NR support are believed to be the key to the formation of cationic Ru species, which is of vital importance for the superior room-temperature CO oxidation activity of the 5Ru/CeO2NR-r catalyst. The higher surface oxygen vacancy concentration on 5Ru/CeO2NR-r than those on the CeO2 NC and NO is also crucial for adsorption/dissociation of oxygen in achieving low-temperature CO oxidation activity.