Supported Co3O4-CeO2 monoliths: effect of preparation method and Pd-Pt promotion on the CO/CH4 oxidation activity

Two structured composite oxides, CO3O4 (30wt%)-CeO2 (70wt%), have been prepared by washcoating commercial cordierite monoliths with a CeO2-gamma Al2O3 layer, on which the active phase Co3O4-CeO2 was added through two different methods: dip-coating from a suspension containing the preformed active oxide or impregnation with a solution of the cobalt and cerium precursors. Morphological characterizations of the monoliths have been performed by BET, and SEM-EDAX analyses. Electronic and reduction properties have been evaluated by XPS and H-2-TPR, respectively. The effect of the preparation method has been investigated in the catalytic oxidation of CO, whereas the promotion by a low content of Pd-Pt has been evaluated in combined CO-CH4 oxidation tests. Four successive CO oxidation cycles performed over the structured Co3O4-CeO2 indicate that the best performing sample is the monolith prepared by dip-coating, whereas that one obtained by impregnation method manifests a certain deactivation upon two consecutive cycles. Accordingly, XPS spectra are consistent with the presence of the active phase Co3O4 in the former, while Co2+ has been identified as the main species in the latter sample.