Study On Catalytic Oxidation Of CO Over Mn-based Oxides

Manganese oxide is among the most popular functional materials due to its low-cost, abundance and environmentally benign properties, and showed the flexible applicability in various fields, like magnetic materials, energy device, catalysis, and battery materials. In this thesis, Mn oxide modified was used as catalysts for CO oxidation. It is of great importance in environmental fields to enhance CO oxidation efficiency by developing efficient catalysts that converting CO into CO₂ at relatively low temperatures since the most production of CO in the total exhaust gas from automobiles is liable during the cool start period. In this work, the modifying method including doping and compositing were adopted to tune the catalytic activity of Mn oxide. The thesis is composed of three parts.（1） The pristine Mn₃O₄ and a series of transition metal doped Mn₃O₄ were synthesized by a facile hydrothermal method. The influence of the doping mental and doping level were investigated. The catalysts were characterized by XRD, SEM, BET, XPS, and H₂-TPR. The catalytic activities of Mn₃O₄ nanocrystals for the CO oxidation were improved after doped with transition metal ions (Co²⁺, Ni²⁺, Cu²⁺and Zn²⁺) due to the enhancement on the mobility of the surface active lattice by the synergy effect between Mn and doped ions. Especially, Cu and Ni doped Mn₃O₄ nanocrystals showed the best activity at 5% doping level. Further investigation of the influence of the doping level was conducted. The results showed that 10% Cu-doped Mn₃O₄ exhibited the best performance with total oxidation of CO achievable at 140℃. The catalytic activities of Mn₃O₄ for CO oxidation decayed with the increasing Ni content.（2） A series of Mn-based mixed oxides, including CuMnOx, CoMn₂O₄ and ZnMn₂O₄, and CO₃O₄ were prepared using absolute ethanol as solvent and urea as precipitants. The catalysts were characterized by TG, XRD, SEM, BET and H₂-TPR. The catalytic activity of CuMnO_x was the best among the as-obtained catalysts. The influence of calcination temperature was investigated and the CuMnO_x calcined at 350℃ showed an optimum performance with total oxidation of CO achievable at 100 ℃. The existence of charge transfer between Cu and Mn cations via Cu-O-Mn bridges was primarily favor for CO oxidation. Meanwhile, the large surface area and the rich active site from amorphous Cu species on the surface are also help for the enhancement of catalytic activity.（3） CuMnO_x with different Au loading were prepared via a deposition-precipitation method and characterized by XRD, SEM, BET, XPS and H₂-TPR. With the increasing of Au loadings, the activity of catalysts was significantly improved.5% Au/CuMnO_x achieved 100% conversion of CO to CO₂ at 44 ℃.