The Nature of the Activity of СoО/ZrO₂ Catalysts in CO Oxidation with Oxygen in Excess Hydrogen

Abstract

The (5–15)%CoO/ZrO₂(T + M) catalysts were studied by XRD and TPR-H₂. In the oxidized samples, 80–90% of cobalt oxide is present in the form of finely dispersed Co₃O₄, which interacts with the support (${\text{Co}}_{x}^{{3 + }}{\text{Co}}_{y}^{{2 + }}{\text{O}}_{z}^{{2 - }}$ clusters), and the rest of it (10–20%) are the Co₃O₄ phase and dispersed CoO. In the CO oxidation to CO₂, the most active samples were CoO/ZrO₂(T + M) containing 10 and 15% cobalt at T₅₀ = 120°C. Nearly 100% conversion of CO to CO₂ was observed on 10%CoO/ZrO₂(T + M) at 160–200°C. The conversion decreases at 220–260°C as a result of competition for oxygen in the oxidations of CO and H₂, and at 280–360°C, as a result of increased consumption of CO in the methanation reaction. The CO oxidation in the range 50–200°C occurs on the clusters localized on the ZrO₂(T) particles. The Co₃O₄ phase in pure oxide and in the 5%CoO/(SiO₂, ZrO₂(M)) catalysts has low activity under these conditions. The temperature dependence of CO conversion was discussed based on the data on the properties of adsorption complexes formed with participation of oxygen clusters and the gas phase.