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On the synergy effect in MoO3-Fe2(MoO4)3 catalysts for methanol oxidation to formaldehyde

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Author

  • Emma Söderhjelm
  • M. P. House
  • Neil Cruise
  • Johan Holmberg
  • M. Bowker
  • Jan-Olov Bovin
  • Arne Andersson

Summary, in English

Methanol oxidation to formaldehyde was studied over a series of Fe-Mo-O catalysts with various Mo/Fe atomic ratio and the end compositions Fe2O3 and MoO3. The activity data shows that the specific activity passes through a maximum with increase of the Mo content and is the highest for Fe2(MoO4)3. The selectivity to formaldehyde, on the other hand, increases with the Mo content in the catalyst. A synergy effect is observed in that a catalyst with the Mo/Fe ratio 2.2 is almost as active as Fe2(MoO4)3 and as selective as MoO3. Imaging of a MoO3/Fe2(MoO4)3 catalyst by SEM and TEM shows that the two phases form separate crystals, and HRTEM reveals the presence of an amorphous overlayer on the Fe2(MoO4)3 crystals. EDS line-scan analysis in STEM mode demonstrates that the Mo/Fe ratio in the amorphous layer is ~2.1 in the fresh catalyst and ~1.7 in the aged catalyst. The enrichment of Mo at the catalyst surface is confirmed by XPS data. Raman spectra give evidence for the Mo in the amorphous material being in octahedral coordination, which is in contrast to the crystalline Fe2(MoO4)3 bulk structure where Mo has tetrahedral coordination. XRD analysis gives no support for the formation of a defective molydate bulk structure. The results presented give strong support for the Mo rich amorphous structure being observed on the Fe2(MoO4)3 crystal surfaces being the active phase for methanol oxidation to formaldehyde.

Publishing year

2008

Language

English

Pages

145-155

Publication/Series

Topics in Catalysis

Volume

50

Issue

1-4

Document type

Journal article

Publisher

Springer

Topic

  • Chemical Engineering
  • Chemical Sciences

Keywords

  • formaldehyde
  • methanol oxidation
  • Fe-Mo-O catalysts
  • electron microscopy
  • iron molybdate
  • XRD
  • TEM
  • HRTEM
  • SEM
  • XPS
  • Raman spectroscopy
  • STEM-EDS

Status

Published

ISBN/ISSN/Other

  • ISSN: 1572-9028