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 Ru
n+ 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.