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Abstract  Cobalt oxide Co3O4 is prepared according to several methods i.e. oxalate decomposition (CoAO), surfactant-assisted precipitation (CoCTAB), sol–gel technique (CoSG) and polymer combustion (CoPVA). The solids are characterized by XRD, FTIR, TPR and TEM analysis. The method via oxalate decomposition (CoAO) appears as that giving the smallest particles nanostructured with an almost monomodal distribution, whereas the CoPVA needs to be calcined at the highest temperature in order to have pure Co3O4. As a consequence on CoPVA the largest particle size is found. The reducibility by H2 of cobalt oxide particles having the smallest (CoAO) and the largest particle size (CoPVA) is found to depend on the particle dimensions and, where the distribution is monomodal, the reduction steps Co3O4 → CoO → Co appear clearly distinct and the temperatures relative to the two reduction steps are well beyond those monitored on microprepared oxide, where only a gross and unique reduction peak is envisaged. [ABSTRACT FROM AUTHOR]