The Effect of the Copper Oxide Content and Support Structure in (0.5-15%)CuO/ZrO2 Catalysts on Their Activity in the CO Oxidation Reaction with Oxygen in an Excess of Hydrogen

摘要

The dependence of the activity of CuO/ZrO2 catalysts in the CO oxidation reaction with oxygen in the presence of an excess of hydrogen and adsorption of CO over them on the CuO content (0.5 to 15%) and the structure of the support ZrO2, monoclinic (De), tetragonal (D cent), or mixed (De + D cent) has been studied. It has been found that the activity of CuO/ZrO2 is associated with the adsorption capacity of the samples for CO at 20A degrees C. Thus, 5%CuO/ZrO2(D cent + De) and 5% CuO/ZrO2(D cent) samples, which exhibit the maximum activity (the CO conversion over them is 80-85% at 160A degrees C), also possess a high chemisorption capacity towards CO (similar to 2.2 x 10(20) molecules/g). At the same time, CuO/ZrO2(De) samples with the CuO contents of 1 and 5% do not chemisorb CO and are inactive in the reaction at 160A degrees C. The CO conversion over them does not exceed 32-36% at 250A degrees C. On the basis of the data obtained by X-ray phase analysis, temperature-programmed reduction with De(2), temperature-programmed CO desorption, and electron paramagnetic resonance, a conclusion has been made that at low temperatures CO oxidation proceeds over Cu (n) O (m) clusters that are located on ZrO2(D cent) 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 CuO phase do not exhibit catalytic activity. The reasons for the low activity of the CuO/ZrO2(De) samples with the CuO contents of 1 and 5% in the CO oxidation and adsorption processes are discussed. The mechanism of the low-temperature CO oxidation with oxygen in an excess of hydrogen over a 5% CuO/ZrO2(D cent + De) catalyst is considered.