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 Cu n O m 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. CuO m 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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