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Adsorption and reaction of methanol on Fe3O4(001)

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  • Matthew D. Marcinkowski, Pacific Northwest National Laboratory
  • ,
  • Kræn C. Adamsen
  • ,
  • Nassar Doudin, Pacific Northwest National Laboratory
  • ,
  • Marcus A. Sharp, Pacific Northwest National Laboratory, Washington State University Pullman
  • ,
  • R. Scott Smith, Pacific Northwest National Laboratory
  • ,
  • Yang Wang, Pacific Northwest National Laboratory
  • ,
  • Stefan Wendt
  • Jeppe V. Lauritsen
  • Gareth S. Parkinson, Technische Universitat Wien
  • ,
  • Bruce D. Kay, Pacific Northwest National Laboratory
  • ,
  • Zdenek Dohnálek, Pacific Northwest National Laboratory, Washington State University Pullman

The interaction of methanol with iron oxide surfaces is of interest due to its potential in hydrogen storage and from a fundamental perspective as a chemical probe of reactivity. We present here a study examining the adsorption and reaction of methanol on magnetite Fe3O4(001) at cryogenic temperatures using a combination of temperature programmed desorption, x-ray photoelectron spectroscopy, and scanning tunneling microscopy. The methanol desorption profile from Fe3O4(001) is complex, exhibiting peaks at 140 K, 173 K, 230 K, and 268 K, corresponding to the desorption of intact methanol, as well as peaks at 341 K and 495 K due to the reaction of methoxy intermediates. The saturation of a monolayer of methanol corresponds to ∼5 molecules/unit cell (u.c.), which is slightly higher than the number of surface octahedral iron atoms of 4/u.c. We probe the kinetics and thermodynamics of the desorption of molecular methanol using inversion analysis. The deconvolution of the complex desorption profile into individual peaks allows for calculations of both the desorption energy and the prefactor of each feature. The initial 0.7 methanol/u.c. reacts to form methoxy and hydroxy intermediates at 180 K, which remain on the surface above room temperature after intact methanol has desorbed. The methoxy species react via one of two channels, a recombination reaction with surface hydroxyls to form additional methanol at ∼350 K and a disproportionation reaction to form methanol and formaldehyde at ∼500 K. Only 20% of the methoxy species undergo the disproportionation reaction, with most of them reacting via the 350 K pathway.

Original languageEnglish
Article number064703
JournalJournal of Chemical Physics
Number of pages10
Publication statusPublished - Feb 2020

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