The nanocrystalline Co3O4 catalysts were prepared via wet-chemical precipitation and dry-solid-state reaction, respectively. To assess the suitability of such CO3O4 as an oxidation catalyst, CO oxidation was taken as model reaction. The best catalyst was obtained by dry grinding route calcined at 300 degrees C, showing the 50% conversion of CO at -92 degrees C, under a stream of normal feed gas containing moisture. Comparing the reaction rate per cobalt oxide mass unit at room temperature (ca. 1.53 mmol g(-1) s(-1)) with the Au-based catalyst in the current literature confirmed the exceptionally high activity of these new materials. The as-synthesized catalysts have been characterized by various techniques in a view of material characterization, as well as to investigate the mechanistic aspects of catalytic reactions. Examination of the surface nature of the materials by X-ray photoelectron spectra (XPS) and temperature-programmed desorption of oxygen (O-2-TPD) shows that O- and lattice oxygen (O2-) are the predominant species at the oxidized surface. In addition, a close parallel between the catalytic activity and the concentration of O- oxygen species indicates that a large amount of more mobile and reactive O- species is the main reason for its enhanced CO oxidation activity. (c) 2012 Elsevier B.V. All rights reserved.