Raman spectroscopy of molybdenum oxides
Part II.† Resonance Raman spectroscopic characterization of the molybdenum oxides Mo4O11 and MoO2
A special sample was prepared by controlled oxidation of MoO2, which contained MoO2, Mo4O11 and MoO3, in order to extend the knowledge about the resonance Raman effect in reduced molybdenum oxides from those close to MoO3 to those close to MoO2. This knowledge is of paramount importance because technical partial oxidation catalysts often contain intermediate Mo oxides of the Magneli type, e.g. Mo4O11, or Mo5O14. The Raman spectra of orthorhombic Mo4O11 and MoO2 have been identified in a Raman microspectroscopic image of 100 single spectra recorded of a mixture of MoO3, MoO2 and Mo4O11. A resonance Raman effect was proven to be responsible for the detection of the molybdenum oxide phases Mo4O11 and MoO2 in dilution with BN when excited at a laser wavelength of 632.8 nm by comparison with Raman microspectroscopic images of the identical sample when excited at 532 nm. The resonance Raman detection of reduced molybdenum oxide phases is discussed in the above mentioned context of their active role in catalytic partial oxidation reactions.