The effect of support morphology on CoOX/CeO2 catalysts for the reduction of NO by CO

When using nanocrystalline oxides as catalytic supports, different nanoshapes have different numbers of oxygen vacancy defects, surface energies, and surface terminations; these properties may affect the dispersion, oxidation state, and therefore catalytic activity of a second supported metal oxide. Here, cobalt oxide domains were synthesized on cerium oxide nanorods, nanocubes, and commercial nanopowder via incipient wetness impregnation of cobalt (II) nitrate hexahydrate at several surface coverages. The resulting materials were examined for their reducibility under CO and H-2 and their reactivity in the catalytic reduction of NO by CO from 200 to 450 degrees C. Activity per total mass of catalyst is highest at intermediate loadings, while activity per Co atom is maximized at the lowest loadings, implicating highly dispersed Co-O-Ce sites as the active species. Across all Co loadings, catalysts with nanorod supports have higher activity than catalysts made with ceria nanoparticles or nanocubes. From X-ray absorption spectroscopy, it was found that the more-active nanorod supports are better able to maintain Co in a partially reduced state under reaction conditions after initial calcination. This stabilization appears to be further correlated with the high number of defects on the ceria nanorods observed via Raman spectroscopy, rather than with properties of the exposed crystal plane, as has been traditionally reported for these materials. These insights may lead to new generations of selective catalysts based on nanocrystal-supported oxides for emissions abatement and other important reactions. (C) 2018 Elsevier Inc. All rights reserved.