High-Pressure CO Phases on Co(0001) and Their Possible Role in the Fischer-Tropsch Synthesis

Bernhard Böller, Patrick Zeller, Sebastian Günther, Joost Wintterlin

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12 Scopus citations

Abstract

The cobalt catalyst used in the Fischer-Tropsch synthesis, under the conditions of the reaction, is covered by a dense adsorption layer in which CO is the main constituent. To obtain insight into the structure of this layer and possible surface phases, CO structures on a Co(0001) model have been investigated by high-pressure scanning tunneling microscopy (STM). The experiments were performed in situ, at CO pressures between 10-9 and 800 mbar and at a temperature of 300 K. Under these conditions, an adsorption-desorption equilibrium was established, reflecting the situation of the reaction. A series of CO surface phases were observed; from 10-9 to 10-7 mbar, a (√3 × √3)R30° structure; between 10-6 and 10-3 mbar, a disordered phase representing a nonstoichiometric, fluctuating (√7 × √7)R19.1° structure; and between 10-2 and 100 mbar, a (2√3 × 2√3)R30° structure. Between 100 and 800 mbar, three moiré structures were observed that were analyzed by a recently developed method. All phases were formed by intact CO molecules. A phase diagram was obtained that allowed us to extrapolate the stability regions of the CO phases to industrial Fischer-Tropsch conditions. We conclude that the reaction operates in the region of the disordered phase at a coverage between 0.43 and 0.50 monolayers of CO.

Original languageEnglish
Pages (from-to)12156-12166
Number of pages11
JournalACS Catalysis
Volume10
Issue number20
DOIs
StatePublished - 16 Oct 2020
Externally publishedYes

Keywords

  • CO Surface Phases
  • CO adsorption
  • Co(0001)
  • Fischer-Tropsch Synthesis
  • High-Pressure STM
  • Scanning Tunneling Microscopy
  • cobalt

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