(583fn) Mechanistic Study of CO Oxidation Over Pure Alpha-Mn2O3 Catalyst- The Combination of Operando Raman and Kinetics

The understanding of spatiotemporal heterogeneities of heterogeneous catalysts has attracted great attention in catalysis research. Different from conventional methods, the emerging Operando techniques, as cutting-edge and powerful tools, can be used for characterizing metal oxide catalysts under realistic reaction conditions with simultaneous real-time online analysis of reaction products. In this study, CO oxidation over a pure a-Mn₂O₃ catalyst was thoroughly studied using the combination of operando Raman spectroscopy and kinetics. The a-Mn₂O₃ nanocrystals with uniform morphology prepared by calcining a self-assembled Mn₃O₄ precursor has proved active (ca. 0.14 molecule×nm^-2×s^-1 at 153 °C) toward CO oxidation at low-temperatures. The reaction orders with respect to CO and O₂ were measured in the temperature range 100-190 °C. Operando and in situ Raman spectroscopy are used in order to determine the near-surface structure of a-Mn₂O₃ nanocrystals during the adsorption and oxidation of CO for the first time. A surface phase-transformation from a-Mn₂O₃ to Mn_jO_k (1<j<2, 1<k<3 and 1<k/j<1.5) intermediate species was observed in gaseous CO with the change of the temperature. In addition, with the combination of the temperature-programmed desorption of O₂ (TPD-O₂), temperature-programmed surface reaction (TRSR) of CO oxidation, Operando Raman spectra and kinetics parameters, we conclude that the oxidation of CO may proceed through the Langmuir-Hinshelwood mechanism (< 200°C) to Mars-van-Krevelen mechanism (>350 °C) with the increasing of reaction temperature. In particular, the adsorbed oxygen is deduced to be responsible for CO oxidation at lower temperatures.