The Preparation, Characterization And The Mechanism Study Of CO Oxidation Over MnO_x-CeO₂Combustion Catalyst

Carbon monoxide （CO） is the most widely distributed pollutant in air with the highest content. CO in the atmosphere mainly sources from the incomplete combustion of fossil fuels, in which vehicle emissions accounted for about80%. At present, low temperature catalytic oxidation is the most popular solution for the treatment of CO pollution. Noble metal catalysts have been widely used due to their high performances and simple preparation methods. However, the high cost and easily poisoned properties of these noble metals have limited their applications and developments. Thus, non-noble metal oxide catalysts have been proposed as a good alternative. MnO_x and CeO₂have gained much research interests for their excellent redox and oxygen storage abilities.In this thesis, MnO_x-CeO₂mixed oxide catalysts with different Mn:Ce molar ratios were prepared with the redox co-precipitation method, and their activities towards CO oxidation were also investigated. Compared to pure Mn-based catalysts, the addition of CeO₂improved the thermal stability significantly; the introduction of water vapor into the atmosphere had no effects on the catalyst structure; the catalysts maintained rather high performances in low temperatures （<200℃）. As suggested by the results of temperature programmed techniques （TPD, TPR and TPSR）, operando Raman spectroscopy and in situ DRIFTs, there are three phases in the catalysts:CeO₂, amorphous MnO_x and Mn-Ce solid solution （the main active phase）. Combining with both the kinetic study and spectral information, the reaction mechanisms for CO oxidation over the MnO_x-CeO₂catalysts in different temperature ranges were revealed:for T﹤130℃, the reaction proceeds via the direct route （CO+Oâ†'CO₂） as well as the formate route （HCOO）; while for T＞130℃, the carbonate route (CO₃^2-) is dominant. Notably, Mars-van-Krevelen mechanism was followed in the whole temperature range. This study shows that MnO_x-CeO₂catalysts could serve as a promising alternative for the noble metal catalysts due to their excellent catalytic performances and thermal stabilities.