Co oxidation with oxygen in the presence of hydrogen on CoO/CeO2 and CuO/CoO/CeO2 catalysts

Abstract

The catalytic activity of the CoO/CeO2 and CuO/CoO/CeO2 systems in selective CO oxidation in the presence of hydrogen at 20–450°C ([CuO] = 1.0–2.5%, [CoO] = 1.0–7.0%) is reported. The maximum CO conversion (X) decreases in the following order: CuO/CoO/CeO2 (X = 98–99%, T = 140–170°C) > CoO/CeO2 (X = 67–84%, T = 230–240°C) > CeO2 (X = 34%, T = 350°C). TPD, TPR, and EPR experiments have demonstrated that the high activity of CuO/CoO/CeO2 is due to the strong interaction of the supported copper and cobalt oxides with cerium dioxide, which yields Cu-Co-Ce-O clusters on the surface. The carbonyl group in the complexes Coδ+-CO and Cu+-CO is oxidized by oxygen of the Cu-Co-Ce-O clusters at 140–160°C and by oxygen of the Co-Ce-O clusters at 240°C. The decrease in the activity of the catalysts at high temperatures is due to the fact that hydrogen reduces the clusters on which CO oxidation takes place, yielding Co0 and Cu0 particles, which are inactive in CO oxidation. The hydrogenation of CO into methane at high temperatures is due to the appearance of Co0 particles in the catalysts.