Operando Raman spectroscopy and kinetic study of low-temperature CO oxidation on an α-Mn2O3 nanocatalyst

alpha-Mn2O3 nanocrystals with uniform morphology prepared by calcining a self-assembled Mn3O4 precursor have proved active (ca. 0.14 molecule nm(-2) s(-1) at 153 degrees C) toward CO oxidation at low temperatures. The reaction orders with respect to CO and O-2 were measured in the temperature range 100-190 degrees C. Operando and in situ Raman spectroscopy are used to determine the near-surface structure of alpha-Mn2O3 nanocrystals during the adsorption and oxidation of CO for the first time. A surface phase transformation from alpha-Mn2O3 to MnjOk (1 < j < 2, 1 < k < 3, and 1 < k/j < 1.5) intermediate species was observed in gaseous CO with the change in temperature. In addition, with the combination of the temperature-programmed desorption of O-2, temperature-programmed surface reaction of CO oxidation, operando Raman spectra, and kinetics parameters, we conclude that the oxidation of CO may proceed through the Langmuir-Hinshelwood mechanism (<200 degrees C) to the Mars van Krevelen mechanism (>350 degrees C) with increasing reaction temperature. In particular, the adsorbed oxygen is deduced to be responsible for CO oxidation at lower temperatures. (C) 2013 Elsevier Inc. All rights reserved.