MOx (M = Mn, Fe, Ni or Cr) improved supported Co3O4 catalysts on ceria–zirconia nanoparticulate for CO preferential oxidation in H2-rich gases

This approach dealt with the modification of our developed Co3O4/Ce0.85Zr0.15O2 catalysts with transition metal oxides MOx (M = Mn, Fe, Ni or Cr) for CO preferential oxidation (CO PROX) in H2-rich gases. Results showed that just MnOx modification remarkably broadened the temperature window of 100% CO conversion, also better than those in the report about Co-Mn composite catalysts from another research group. And even in the presence of H2O and CO2, the 175–225 °C temperature range for almost 100% CO conversion can be achieved over the optimized catalyst. Moreover, the addition of MnOx significantly improved the catalytic activity and selectivity, which was dramatically better than those of the supported MnOx or Co3O4 catalysts on ceria–zirconia nanoparticulate, indicating the existence of the remarkable Co-Mn synergistic effect. The MnOx modified supported Co3O4 catalysts exhibited outstanding catalytic properties for CO PROX reaction, which was strongly dependent on the reducibility and dispersion of the active species affected by the Co/Mn atomic ratio and loading. The XRD and H2-TPR techniques were performed to reveal the effect of structure–activity relationship on the catalytic properties. The analytic results presented that Co3+ was the main active species for CO PROX reaction, and the existence of Mn4+ and Mn3+ was also favorable to the reaction. The XRD and H2-TPR characterization results affirmed the existence of strong interaction between Co and Mn, increasing the ratio of Co3+/Co2+ resulted from the electron transfer between Co2+ and Mn4+. Besides the improvement of Co3O4 dispersion and the enlargement of the Co3+/Co2+ ratio through Co-Mn interaction, the addition of MnOx could improve the stability of the ceria–zirconia support through the metal–support interaction. As a result, the CO selective oxidation reaction was efficiently improved. The 16 wt.%Co3O4-MnOx/Ce0.85Zr0.15O2 (Co/Mn = 8:1) could be a quite potential catalyst for eliminating trace CO from H2-rich gases.

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► MnOx remarkably enhances catalytic activity of supported Co3O4 catalysts for CO PROX.
► The appropriate Co/Mn ratio and loading are essential to the modified catalysts.
► The active species reducibility and dispersity strongly affect catalytic properties.
► Co-Mn interaction significantly improves the Co3O4 dispersion and the reducibility.
► Co3+ is main active species, and the presence of Mn4+/Mn3+ benefits for the reaction.