The Effect of the Copper Oxide Content and Support Structure in (0.5−15%)СuО/ZrO2 Catalysts on Their Activity in the CO Oxidation Reaction with Oxygen in an Excess of Hydrogen
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The dependence of the activity of СuO/ZrO2 catalysts in the CO oxidation reaction with oxygen in the presence of an excess of hydrogen and adsorption of СО over them on the CuO content (0.5 to 15%) and the structure of the support ZrO2, monoclinic (М), tetragonal (Т), or mixed (М + Т) has been studied. It has been found that the activity of CuO/ZrO2 is associated with the adsorption capacity of the samples for СО at 20°С. Thus, 5%CuO/ZrO2(Т + М) and 5% CuO/ZrO2(Т) samples, which exhibit the maximum activity (the СО conversion over them is 80–85% at 160°С), also possess a high chemisorption capacity towards CO (~2.2 × 1020 molecules/g). At the same time, CuO/ZrO2(М) samples with the CuO contents of 1 and 5% do not chemisorb СО and are inactive in the reaction at 160°С. The СО conversion over them does not exceed 32–36% at 250°С. On the basis of the data obtained by X-ray phase analysis, temperature-programmed reduction with Н2, temperature-programmed СО desorption, and electron paramagnetic resonance, a conclusion has been made that at low temperatures СО oxidation proceeds over CunOm clusters that are located on ZrO2(Т) crystallites. With the increase in the copper oxide content from 0.5 to 5%, the activity of the clusters increases, while the reaction temperature decreases. CuOm oxo complexes and particles of the СuO phase do not exhibit catalytic activity. The reasons for the low activity of the CuO/ZrO2(М) samples with the CuO contents of 1 and 5% in the СО oxidation and adsorption processes are discussed. The mechanism of the low-temperature СО oxidation with oxygen in an excess of hydrogen over a 5% CuO/ZrO2(Т + М) catalyst is considered.
KeywordsСО oxidation and adsorption CuO/ZrO2 catalysts monoclinic and tetragonal ZrO2 and their mixture
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