Comparative atomic-scale analysis of promotional effects by late 3d-transition metals in MoS2 hydrotreating catalysts

Jakob Kibsgaard, Anders Tuxen, Kim G. Knudsen, Michael Brorson, Henrik Topsoe, Erik Laegsgaard, Jeppe V. Lauritsen, Flemming Besenbacher

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The promotion of the activity of MoS2-based hydrotreating catalysts by various first-row transition metals exhibits a typical variation referred to as a volcano plot. Co and Ni are seen to substantially promote the catalytic activity of MoS2, whereas the neighboring first-row metals promote reactivity to a much lesser extent, or not at all. In order to provide a better atomistic understanding of the catalytic synergies, we perform here a comparative scanning tunneling microscopy (STM) analysis of the atomic-scale structure and morphology of MoS2 nanoclusters doped with the first-row transition metals: Fe, Co, Ni, and Cu. We reveal that addition of all four dopant metals results in the formation of mixed-metal "Co-Mo-S"-type structures shaped as single-layer hexagonally truncated triangular MoS2-like nanoclusters. The modification of the preferred nanocluster equilibrium morphology is explained as a direct consequence of a favored substitution of dopant metal atoms into the S-edges of MoS2. The degree of truncation and the edge dispersion are, however, found to depend greatly on the type of dopant atom since the relative length of the dopant-stabilized edges decreases with the number of valence shell electrons of the dopant transition metal. A comparison of the observed atomic structure and morphology with the hydrotreating activity measured for industrial-style prepared Me-Mo-S catalysts (Me = Fe, Co, Ni, and Cu) supported on carbon reveals that two parameters are relevant to describe the promotional behavior: (i) a geometric parameter, which relates to the relative number of promoted and unpromoted sites in the Me-Mo-S nanoclusters, and (ii) a more conventional parameter relating to bonding and adsorption strength, i.e., describing the intrinsic activity of the particular Me-doped S-edge.
Original languageEnglish
JournalJournal of Catalysis
Volume272
Issue number2
Pages (from-to)195-203
Number of pages9
ISSN0021-9517
DOIs
Publication statusPublished - 2010
Externally publishedYes

Keywords

  • Catalysis
  • Activity measurements
  • Co-mo-s
  • Hydrodesulfurization
  • Hydrotreating
  • Mos2
  • Nanoclusters
  • Nanoparticles
  • Promoters
  • Scanning tunneling microscopy

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