Abstract: The influence of calcination and pretreatment conditions on the structure of Co₃O₄ and its activity for CO oxidation were studied. TG analysis indicated that the precursor of Co₃O₄ prepared by a precipitation method was present in the form of cobalt hydroxide carbonate, calcination of which within the temperature range of 150–400 ^oC in air resulted in the formation of cubic phase Co₃O₄. N₂ adsorption-desorption, powder X-ray diffraction, transmission electron microscopy, and activity test results showed that the prepared Co₃O₄ samples were comprised of nanoparticles, with the specific surface area and size distribution closely related to the calcination temperature. Over these samples, a size dependence of the catalytic activity for CO oxidation was clearly observed. As identified by positron annihilation lifetime spectrum, low temperature oxygen temperature-programmed desorption, and durability testing for CO oxidation, pretreatment of Co₃O₄ in N₂ within the temperature range 150–250 ^oC favors the formation of surface oxygen vacancy clusters, the occurrence of which would be beneficial for the adsorption and activation of O₂, and also for the catalytic oxidation of CO. Meanwhile, the reconstruction of oxygen vacancies on the surface of Co₃O₄, induced by the pretreatment process, was also discussed.

Key words: Tricobalt tetraoxide, Calcination, Pretreatment, Oxygen vacancy, Carbon monoxide oxidation