Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

Abhijeet Gaur, Max Schumann, Kristian Viegaard Raun, Matthias Stehle, Pablo Beato, Anker Degn Jensen, Jan‐Dierk Grunwaldt, Martin Høj*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

The structural changes of an iron molybdate/molybdenum oxide (Mo/Fe=2.0) catalyst for the selective oxidation of methanol to formaldehyde were studied using combined operando X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) as well as operando Raman spectroscopy. Under operating conditions, the Mo K‐edge XANES spectra showed a transition from a mixture of α‐MoO3 and Fe2(MoO4)3 towards only Fe2(MoO4)3. XRD and Raman spectroscopy also showed disappearance of the α‐MoO3 phase with time on stream. The results evidenced that the α‐MoO3 component evaporated completely, while the Fe2(MoO4)3 component remained stable. This was linked to a decrease in catalytic activity. Further studies unraveled that the rate of α‐MoO3 evaporation increased with increasing MeOH concentration, decreasing O2 concentration and increasing temperature. The simultaneous measurements of catalytic activity and spectroscopy allowed to derive a structure‐activity relationship showing that α‐MoO3 evaporation needs to be prevented to optimize MoO3‐based catalysts for selective oxidation of methanol.
Original languageEnglish
JournalChemCatChem
Volume11
Issue number19
Pages (from-to)4871-4883
Number of pages13
ISSN1867-3880
DOIs
Publication statusPublished - 2019

Keywords

  • Formaldehyde
  • Operando XAS/XRD
  • Normalized difference edge analysis
  • Raman spectroscopy
  • Selective oxidation

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