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Iron molybdates (mixed oxides of iron and molybdenum) are used to effect the partial oxidation of methanol to formaldehyde. In the present work, Raman spectroscopy was used to characterize supported mixed iron/molybdenum oxide catalysts. These supported catalysts were prepared by impregnation of silica and alumina with solutions of ferric nitrate and ammonium molybdate. The Raman spectroscopic studies were employed to obtain information about the influence of variations in the preparation protocol on the properties of the final catalysts. The spectra were indicative of surface enrichment of one species [(MoO3 or Fe2(MoO4)3)] and also provided evidence for catalyst-support interactions.

Raman spectra of both supported and unsupported Fe/Mo/O catalysts of the type used for the partial oxidation of methanol to formaldehyde were obtained while this reaction was proceeding over the catalyst surface. No changes in band locations or relative peak intensities associated with these mixed metal oxides were detected in the presence of reactant and product species. Moreover, no spectral features which could be attributed to adsorbed species could be detected under reaction conditions. Band intensities in the Raman spectra were related to the extent to which the catalysts were reduced; fully oxidized catalysts were stronger Raman scatterers than partially reduced catalysts. Although differences in color were noted between fresh and used catalysts, the Raman and Mossbauer spectra of these catalysts were identical. Calcination of used catalysts in an oxygen environment at 500 °C was sufficient to restore partially reduced catalysts to their original fully oxidized states.