Catalytic CO Oxidation over Well-Defined Cobalt Oxide Nanoparticles: Size-Reactivity Correlation

Co nanoparticles of well-defined size were synthesized by temperature-controlled injection of Co₂(CO)₈ into dichlorobenzene. After intercalation into mesoporous MCF-17 and temperature-programmed oxidation, Co₃O₄/MCF-17 model catalysts were obtained with cobalt oxide particle sizes varying between 3.5 and 12.2 nm. We demonstrate here the occurrence of a distinct particle size effect for the CO oxidation. Maximum reaction rates of about 0.77 nm^–2 s^–1 at 150 °C were observed for Co₃O₄ particles with a size in the range of 5 to 8 nm. The reaction rates decreased for either smaller or larger sizes. X-ray photoelectron spectroscopy allowed establishing a clear correlation between the Co³⁺ trivalent oxidation state and the CO oxidation rate.