Observation of the Reversible Phase-Transformation of -Mn2O3 Nanocrystals during the Catalytic Combustion of Methane by in Situ Raman Spectroscopy

摘要

Real-time in situ Raman spectroscopy is used to probe the near-surface structure of -Mn2O3 nanocrystals during methane combustion for the first time. A surface phase-transformation from -Mn2O3 to Mn3O4-like species, as evidenced by the formation of a single band at 648 cm~-1, was observed only at or above 400 C in the presence of pure He or in the mixture of O2 + CH4. This modification is probably due to the loss of lattice oxygen at high temperatures that leads to the surface reconstruction. Very interestingly, a reversible phase-transformation was observed with decreasing the temperature to 25 C. The phase-change at the near-surface is suggested to be associated with the activating C-H bond of methane.