Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agents and calcination temperature on the catalytic activity for methane oxidation

Crystalline cobalt oxides were prepared by a precipitation method using three different precipitationagents, IJNH4)2CO3, Na2CO3 and COIJNH2)2. Cobalt oxide nanoparticles corresponding to a Co3O4 loadingof 30 wt% were also deposited over high-surface area nanocrystalline ceria by the same precipitationagents. The effect of calcination temperature, 350 or 650 °C, on the morphological and structural propertieswas evaluated. Characterization by BET, XRD, SEM, TEM, Raman spectroscopy, H2-TPR, XPS andNH3-TPD was performed and the catalytic properties were explored in the methane oxidation reaction.The nature of the precipitation agent strongly influenced the textural properties of Co3O4 and theCo3O4–CeO2 interface. The best control of the particle size was achieved by using COIJNH2)2 thatproduced small and regular crystallites of Co3O4 homogeneously deposited over the CeO2 surface. Such aCo3O4–CeO2 system precipitated by urea showed enhanced low-temperature reducibility and high surfaceCo3+ concentration, which were identified as the key factors for promoting methane oxidation atlow temperature. Moreover, the synergic effect of cobalt oxide and nanocrystalline ceria produced stablefull conversion of methane in the entire range of investigated temperature, up to 700–800 °C, at whichCo3O4 deactivation usually occurs.