Stability of Iron-Molybdate Catalysts for Selective Oxidation of Methanol to Formaldehyde: Influence of Preparation Method

Kristian Viegaard Raun, Lars Fahl Lundegaard, Pablo Beato, Charlotte Clausen Appel, Kenneth Nielsen, Max Thorhauge, Max Schumann, Anker Degn Jensen, Jan-Dierk Grunwaldt, Martin Høj*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Iron molybdate/molybdenum oxide catalysts with varying content of Mo (Mo/Fe = 1.6 and 2.0) were synthesized by a mild hydrothermal method and structurally characterized by XRD, XPS, Raman spectroscopy, SEM–EDX, BET and ICP-OES. The stability of the prepared catalysts in selective oxidation of methanol to formaldehyde was investigated by catalytic activity measurements for up to 100 h on stream in a laboratory fixed-bed reactor (5% MeOH, 10% O2 in N2, temp. = 380–407 °C). Excess MoO3 present in the catalyst volatilized under reaction conditions, which lead to an initial loss of activity. Interestingly, the structure of the excess MoO3 significantly affected the stability of the catalyst. By using low temperature hydrothermal synthesis, catalysts with the thermodynamically metastable hexagonal h-MoO3 phase was synthesized, which yielded relatively large crystals (2–10 µm), with correspondingly low surface area to volume ratio. The rate of volatilization of MoO3 from these crystals was comparatively low, which stabilized the catalysts. It was furthermore shown that heat-treatment of a spent catalyst, subject to significant depletion of MoO3, reactivated the catalyst, likely due to migration of Mo from the bulk of the iron molybdate crystals to the surface region.
Original languageEnglish
JournalCatalysis Letters
Volume150
Pages (from-to)1434–1444
ISSN1011-372X
DOIs
Publication statusPublished - 2020

Keywords

  • Formox
  • Formaldehyde
  • Iron molybdate
  • Hexagonal MoO3
  • Catalyst deactivation

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