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 Co 2 (CO) 8 into dichlorobenzene. After intercalation into mesoporous MCF-17 and temperature-programmed oxidation, Co 3 O 4 /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 Co 3 O 4 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 Co 3+ trivalent oxidation state and the CO oxidation rate.