Mn_xO_y,TiO₂ Modification On Structure And Catalytic Properties Of CuO/γ-Al₂O₃ Catalysts

Part I:X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), laser raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and in-situ infrared spectroscopy (in-situ FT-IR) were used to characterize the different effect of precursors and calcination atmosphere on the CuO-MnxOy/γ-Al2O3 catalysts for physical and chemical properties, and the activities of samples in NO+CO model reaction were also tested. The following conclusions:(1) XRD results show that:acetate co-impregnated samples were all detected the diffraction peaks of copper species, and the formation of crystalline copper species may be due to the reduction of acetate; nitrate co-impregnated samples were not detected the existence of crystal copper species, indicating that the copper species were well-dispersed on the surface ofγ-Al2O3. According to the H2-TPR results, a large amount of-Cu-O-Mn-species were formed in nitrate co-impregnated samples.(2) Combination of XRD, LRS, and XPS results, the valence of copper and manganese in four different samples were analyzed:for acetate co-impregnated samples the valence of manganese mainly existed in Mn3+ form, among them, copper species existed in the form of Cu2+ for samples calcined in air, while Cu2+, Cu+, and Cu0 coexisted in samples calcined in nitrogen; for nitrate co-impregnated samples manganese species mainly existed in Mn4+ form for samples calcined in nitrogen, while Mn4+, Mn3+ coexisted in samples calcined in air, and copper species existed in the form of Cu2+.(3) The results of NO+CO model reaction indicated that:for the fresh samples of acetate co-impregnated there would be a jump of activity between 250 to 300℃, it may be due to the CO spillover effect during the reaction; after CO pretreatment four different samples'reaction activities were all significantly increased, but the activities of nitrate co-impregnated samples were more excellent than acetate co-impregnated samples, mainly due to the existence of more -Cu-O-Mn-species in nitrate co-impregnated samples, making the pretreated samples to generate more -Cu-□-Mn-species, namely, the formation of SSOV, which is conducive to the activity of NO+CO reaction increased.PartⅡ:The influence of titania on the properties of CuO/γ-Al2O3 was investigated using X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), laser raman spectroscopy (LRS), CO oxidation reaction, and NO+CO reaction. It is indicated that:(1) When pre-loading amount of TiO2 was higher than its dispersion capacity on the surface ofγ-Al2O3, crystalline TiO2 can still not be found from XRD patterns, but can be found from Raman patterns. It could be suggested that the dispersion capacity of TiO2 on y-alumina is around 0.52mmol/100m2γ-Al2O3.(2) With increasing TiO2 content, reduction temperature of CuO decreased, indicating that the addition of TiO2 can promote the reduction of CuO, probably due to the addition of TiO2 blocking the interaction between CuO and the carrier.(3) The presence of crystalline TiO2 can increase the activity of CO oxidation reaction, but little impact on NO+CO reaction.