CoOx-decorated CeO2 heterostructures: effects of morphology on their catalytic properties in diesel soot combustion

Abstract

The effect of the morphology, which exposes different crystal planes, on the physicochemical properties and catalytic activity in diesel carbon soot oxidation was studied using CoO_x-decorated CeO₂ (CoCeO₂) heterostructured catalysts, such as nanorods (NRs), nanocubes (NCs), and nanoparticles (NPs). The CoO_x/CeO₂ nanorods (CoCeO₂-NR) showed superior carbon soot combustion activity at lower temperatures to CoCeO₂-NCs and CoCeO₂-NPs under both tight and loose contact modes with soot combustion temperatures (T₅₀) of 321 and 494 °C, respectively. A comprehensive analysis by means of X-ray diffraction, Raman spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, in situ X-ray absorption fine structure, temperature-programmed reduction, oxygen storage/release measurements, and density functional theory calculations revealed that the improved activity of CoCeO₂-NRs is mainly ascribed to the high oxygen release rate and strong redox capability of the supported Co species, with complete reversibility. This originates from the high reactivity of oxygen atoms on (110) surfaces, compared to (100) and (111) surfaces over CeO₂. Additionally, CoCeO₂-NRs displayed durability and recyclability without any significant loss of catalytic activity or structural change. These insights will aid in the rational design of practical catalysts for the purification of diesel exhaust and other important transformations.