Raman spectroscopy of molybdenum oxides Part II. Resonance Raman spectroscopic characterization of the molybdenum oxides Mo4O11 and MoO2

Abstract

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.