Operando Raman Spectroscopy for Determining the Active Phase in One- Dimensional Mn1−xCexO2±y Nanorod Catalysts during Methane Combustion

One-dimensional Mn 1− x Ce x O 2± y nanorod catalysts were synthesized and characterized by X-ray diffraction (XRD) and operando Raman spectroscopy to determine the active phase during methane combustion. Thermal- and reaction-induced phase-transformation determined by operando Raman indicated that the MnO x domain in Mn 1− x Ce x O 2± y is the active phase for methane combustion. Besides the peak near 458 cm −1 attributed to F 2g mode in CeO 2, two new features, corresponding to O vacancies between 590 and 610 cm −1 and Mn 3 O 4 -like species (Mn−O−Mn) near 640 cm −1 were observed for Mn 1− x Ce x O 2± y nanocrystal catalysts. The number of O vacancies in CeO 2 and the surface concentration of MnO x are mainly responsible for methane combustion. Moreover, Mn 1− x Ce x O 2± y nanocrystal catalysts show superior activity and stability as compared to α-Mn 2 O 3; especially, Mn 0.6 Ce 0.4 O 2±y exhibits the highest activity among all samples.