Abstract
Catalysts of CoOx and Au/CoOx (x is a stoichiometry between 1.00 and 1.33) were prepared to study their catalytic activity towards the CO oxidation. The oxidation state of cobalt ions in these catalysts was evaluated with TPR (the temperature programmed reduction) technique. TPR reduction of CoOx samples was found to proceed through two resolvable steps, i.e., CoOx into CoO at 570 K and CoO to metallic Co at 640 K. The relative area observed for these two peaks in TPR traces was used to determine the stoichiometry x in freshly prepared catalysts. Their catalytic activities were tested in a fixed bed flow reactor. Measured activity generally increased with the stoichiometry x in catalysts of CoOx and Au/CoOx. The variation in activity was interpreted with an oxidation of CO by two kinds of oxygen species, i.e., oxygen molecularly adsorbed on CoOx surface and active oxygen ions in the lattice of Co3O4 spinel structures. An impregnation of Au particles on the surface of CoOx significantly enhances its catalytic activity. The promotion comes from an effective adsorption of CO on the interface between the particles and the surface.