Studies On The Characterization And The Properties Of CuO-Mn_xO_y/γ-Al₂O₃ Catalyst For NO Catalytic Reduction

PartⅠ:The properties of CuO/γ-Al2O3, MnxOy/γ-Al2O3, CuO-MnxOy/γ-Al2O3 catalysts before and after CO pretreatment were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), CO-temperature programmed reduction (CO-TPR) and Laser Raman spectroscopy (LRS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), NO-temperature programmed desorption (TPD), Fourier transform infrared (FT-IR). The activities of the treated catalysts were measured in NO+CO model reaction. Based on the above studies, some conclusions could be drawn:1,The fresh CuO/γ-Al2O3, MnxOy/γ-Al2O3 and CuO-MnxOy/γ-Al2O3 catalysts exhibited poor catalytic activity for NO+CO model reaction. After CO pretreatment, the catalytic performance of CuO/γ-Al2O3 and MnxOy/γ-Al2O3 could not be improved obiviously, but the CO-pretreated CuO-MnxOy/γ-Al2O3 catalyst exhibited higher catalytic activity than did other catalysts.2,Combined with H2-TPR,Raman,UV-vis DRS results and our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well asγ-Al2O3 surface has been proposed. Cu and Mn ions occupied the octahedral vacant sites ofγ-Al2O3, and with the capping oxygen on the top of metal ions to keep the charge conservation. For the fresh CuO/γ-Al2O3 and MnxOy/γ-Al2O3 catalysts, the -Cu-O-Cu- and -Mn-O-Mn- species were formed on the surface ofγ-Al2O3, respectively, but for the fresh CuO-MnxOy/y-Al2O3 catalyst,-Cu-O-Mn-species existed on the surface of y-AlO3. After CO-pretreatment,-Cu-□-Cu- and -Mn-□-Mn-(□represents surface oxygen vacancy (SOV)) species would be formed in CO-pretreated CuO/y-Al2O3 and CO-pretreated MnxOy/y-Al2O3 catalysts, respectively, while -Cu-□-Mn- species existed in CO-pretreated CuO-MnxOy/y-Al2O3. Herein, a new concept, Surface Synergetic Oxygen Vacancy (SSOV) for describing the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO-pretreated CuO-MnxOy/y-Al2O3 catalyst. The current study suggested that the properties of the SSOVs in CO-pretreated CuO-MnxOy/γ-Al2O3 catalyst were significantly different from SOVs formed in CO-pretreated CuO/γ-Al2O3 and MnxOy/y-Al2O3 catalysts and the SSOVs might play an important role in NO reduction by CO.3,CO pretreatment at 325℃for 1 h results in the reduction of disperesed CuO to disperesed Cu2O and partial dispersed Cu2O to Cu0. Moreover, some dispersed MnxOy was reduced to the dispersed MnO in the MnxOy/y-Al2O3 and CuO-MnxOy/y-Al2O3 catalysts.4,NO-TPD results suggested wherther surface synergetic oxygen vacancy (SSOV) or surface oxygen vacancy (SOV) favored NO dissociation. NO+CO-in situ FTIR results suggested the temperature of NO dissociation was closely related to the catalytic performance, the lower temperature of NO dissociation would give rise to the higher catalytic activity. SSOV more favored NO dissociation than SOV.5,The competitive adsorption experiments on CO-CuO/γ-Al2O3, CO-MnxOy/y-Al2O3 and CO-CuO-MnxOy/y-Al2O3 samples suggested that NO mainly adsorbed on Mn2+ and CO on Cu+ sites.Part II:The effects of precursors and calcining atmosphere on the CuO-MnxOy/y-Al2O3 catalysts were investigated by means of XRD, XPS, Raman, H2-TPR. The activity tests of catalysts for NO+CO model reaction were performed. Meanwhile, the effects of CO pretreated co-impregnated samples were also studied in this part of research.1) According to the XRD results, crystal CuO, CU2O and Cu are all detected in the 06CuyMnAl-A-N2 samples, compared to only crystal CuO species in 06CuyMnAl-A-air samples. The existence of copper species in low valence state was probably related to the reducing properties of the acetate. However, both copper oxide and manganese oxide from nitrate precursors were all well-dispersed on the surface ofγ-Al2O3. In conclusion, copper oxides from nitrate precursors were more likely to disperse on the surface ofγ-Al2O3 than those from acetate precursors.2) For the samples calcined in air, NO+CO model reaction activities results about nitrate precursors samples and acetate precursors samples showed that, the states of copper species and interactions between copper species and manganese species were possibly two great factors in activity. The redox equilibrium Cu2++ Mn3+ (?) Cu++ Mn4+ probably existed in the catalytic process, which should be responsible for the presence of oxygen vacancy and advancement of catalytic activities.3) Copper and manganese mixed oxides possibly existed in both co-impregnated nitrate and acetate precursors samples, which infered the presence of-Cu-O-Mn-, and the samples were pretreated by CO, then SSOV would form. The activities of NO+CO model reaction in low temperature region are distinctively promoted after CO pretreatment, which substantiated the positive effect of SSOV to NO+CO reaction again.