The Preparation Of Different Metal Cation Doped MnO_x And Its Catalytic Activity In Co Oxidation

Low-temperature catalytic oxidation of CO is a reaction which has important applications in many fields. Currently, the main industrial catalyst used for CO oxidation is the noble metal catalyst which has higher catalytic activity and higher stability. From a viewpoint of saving precious metals and reducing costs, it is of importance to develop non-precious metal catalysts with high catalytic activities for CO oxidation at low temperature. The dissertation focuses on the preparation of various metal ions doped MnOx catalysts and its CO oxidation activity, and is composed of four parts.In the first part, a series of KMn/Al2O3catalysts were synthesized by the impregnation method and characterized by X-ray diffraction (XRD), N2adsorption, X-ray photoelectron spectroscopy (XPS) and other spectroscopic techniques. Effects of catalyst composition, molar ratios of potassium and manganese and calcination temperature on catalytic activity of KMn/Al2O3catalysts for CO oxidation were also investigated. It was found that the calcination temperature could exert a significant influence on catalytic activity in CO oxidation via the catalyst specific surface area, the presence of manganese oxide as well as its dispersion. The catalyst calcined at500℃, which the supported manganese mainly existed as β-MnO2with high dispersion and easily reduced, showed high catalytic activity. Adding a small amount of K to the manganese catalyst could improve the dispersion of manganese oxide, the ratio of surface lattice oxygen and its reactivity, thus significantly improved the catalyst activity. However, adding excessive K would lead to a conversion from β-MnO2to α-MnO2, thus a decrease in CO conversion could be seen. The highest catalytic activity could be achieved when a potassium-manganese ratio of1:10was used.In the second part, a series CuMnOx catalysts prepared by different methods were investigated for CO oxidation reaction. The catalysts were characterized by X-ray diffraction (XRD), N2adsorption, X-ray photoelectron spectroscopy (XPS) and other methods. It was found that adding a small amount of copper to MnOx could significantly improve the catalyst activity in the CO oxidation, while a large amount of copper would result in a decrease in the CO conversion. The supported copper is highly dispersed on MnOx when Cu-containing was less than6%, while aggregated copper with large particles could be seen when the copper content was greater than12%. Highly dispersed copper as well as the synergy with MnOx play an important role on the higher catalytic activity. Compared with the catalyst by other method, Cu/OMS-2 catalysts prepared by the impregnation method containing more lattice oxygen, more easily reduced small copper oxide particles, the larger specific surface area and pore volume, thus showed a higher catalytic activity.In the third part, a series of Cc-doped MnOx catalysts were synthesized by different methods. The influences of the catalyst preparation method and the molar ratio of cerium and manganese on catalytic performance for the CO oxidation were investigated. The X-ray diffraction (XRD), N2physical adsorption, X-ray photoelectron spectroscopy (XPS) and other methods were used to characterize the catalysts. It was found that adding a small amount of cerium to MnOx could enhance the oxygen storage capacity and improve the reactivity of lattice oxygen and decrease the reduction temperature, thus significantly improved CO oxidation activity. And adding a lot of cerium would form aggregated cerium oxide with large particles, resulting in a decrease in catalytic activity. The higher catalytic activity could be obtained when amorphous MnOx was used as the support to prepare Ce/MnOx catalyst due to its high activity lattice oxygen as well as high dispersion of Mn and Ce.In the fourth part, a series of CeMnOx/SBA-15catalysts prepared by the impregnation method were investigated for CO oxidation, and characterized by X-ray diffraction (XRD), N2adsorption, H2temperature programmed reduction (H2-TPR) and other methods. The characterizations showed that the Mn species existed as MnO2with a Mn-loading less than10%are encapsulated within the channels of SBA-15, while a high amount of manganese would form aggregated MnO2with large particles located outside the channels of SBA-15. Small MnO2particles encapsulated in the pores of SBA-15was suggested as the high active component for CO oxidation. The calcination temperature can affect the decomposition of the manganese precursor, the presence of MnOx and its restore nature, thus exert a significant influence on catalytic activity. The catalyst calcined at400℃, in which the Mn existed mainly as small MnO2particles and easily being reduced, showed higher catalytic activity. Add a small amount of cerium to supported MnOx can significantly improved the dispersion of MnOx, the reactivity of lattice oxygen as well as the reduction of the manganese oxide, thus a higher CO oxidation activity can be obtained.