Raman spectroscopy of iron molybdate catalyst systems:: Part I. Preparation of unsupported catalysts

Abstract

Raman spectroscopy was used to characterize unsupported iron/molybdenum oxide catalysts of the type used for the partial oxidation of methanol to formaldehyde. Bulk catalysts were prepared by coprecipitation from solutions of ferric nitrate and ammonium molybdate. The Raman spectra of the catalysts contained bands characteristic of Fe 2(MoO 4) 3 and MoO 3. For unsupported catalysts with Mo/Fe ratios greater than 1.5, the relative intensities of the MoO 3 and Fe 2(MoO 4) 3 peaks in the Raman spectra were approximately proportional to the corresponding atomic ratio. These catalysts are comprised of Fe 2(MoO 4) 3 and MoO 3 which are formed in the calcination step of the preparation protocol. Raman spectra indicate that a solid phase reaction begins as the precipitates are heated at 105 °C. At 125 °C Raman bands characteristic of Fe 2(MoO 4)a were observed. At 250 °C bands corresponding to MoO 3 appeared. In situ and ex situ spectroscopic studies were used to obtain further information about the influence of variations in the preparation protocol on the properties of the final catalysts.