Sulfur adsorption and sulfidation of transition metal carbides as hydrotreating catalysts

Ping Liu, José A. Rodriguez, James Muckerman

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

The formation of MoSxCy compounds has been observed on/in the surface of molybdenum-sulfide catalysts during the hydrodesulfurization (HDS) process, and it is a major factor for determining the activity of molybdenum-carbide catalysts. Density functional theory (DFT) was employed to investigate the adsorption of sulfur and sulfidation of transition metal carbides from groups 4-6 in the periodic table, including extended surfaces [MC(0 0 1) (M = Ti, V, Mo, Ta)], nanocrystals [M14C 13 (M = Ti, V, Mo)] and metcar [M8C12 (M = Ti, V, Mo)] nanoparticles. It was found that with increasing carbon/metal ratio, the reactivity of the metal carbides towards sulfur decreased in the sequence: Mo2C > M14C13, M8C12 > MC(0 0 1). In terms of sulfidation, M8C12 and MC(0 0 1) display a stronger resistance than M14C13. The presence of corner or edge sites in the M14C13 nanocrystal favors the formation of MoSxCy compounds. Following Sabatier's principle, our results suggest that flat MC(0 0 1) surfaces are too inert to catalyze HDS reactions, while M14C13 is too active to resist the sulfidation that leads to degradation of the carbides. For reactions involving sulfur and sulfur-containing molecules, nanoparticles adopting the special geometry of metcars should display a better catalytic activity than the corresponding bulk materials and carbide nanoparticles that have a cubic-based structure like nanocrystals. Indeed, DFT calculations indicate that Ti 8C12 and Mo8C12 are good catalysts for the HDS of thiophene.

Original languageEnglish
Pages (from-to)116-124
Number of pages9
JournalJournal of Molecular Catalysis A: Chemical
Volume239
Issue number1-2
DOIs
Publication statusPublished - Sep 14 2005

Fingerprint

sulfidation
Sulfur
carbides
Hydrodesulfurization
Transition metals
Carbides
sulfur
transition metals
Nanocrystals
Adsorption
catalysts
nanocrystals
Catalysts
adsorption
Nanoparticles
nanoparticles
Density functional theory
Metals
molybdenum carbides
Molybdenum

Keywords

  • Density functional theory
  • Metal carbide
  • Metcar
  • Nanocrystal
  • Sulfidation
  • Sulfur adsorption

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Materials Science (miscellaneous)

Cite this

Sulfur adsorption and sulfidation of transition metal carbides as hydrotreating catalysts. / Liu, Ping; Rodriguez, José A.; Muckerman, James.

In: Journal of Molecular Catalysis A: Chemical, Vol. 239, No. 1-2, 14.09.2005, p. 116-124.

Research output: Contribution to journalArticle

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AB - The formation of MoSxCy compounds has been observed on/in the surface of molybdenum-sulfide catalysts during the hydrodesulfurization (HDS) process, and it is a major factor for determining the activity of molybdenum-carbide catalysts. Density functional theory (DFT) was employed to investigate the adsorption of sulfur and sulfidation of transition metal carbides from groups 4-6 in the periodic table, including extended surfaces [MC(0 0 1) (M = Ti, V, Mo, Ta)], nanocrystals [M14C 13 (M = Ti, V, Mo)] and metcar [M8C12 (M = Ti, V, Mo)] nanoparticles. It was found that with increasing carbon/metal ratio, the reactivity of the metal carbides towards sulfur decreased in the sequence: Mo2C > M14C13, M8C12 > MC(0 0 1). In terms of sulfidation, M8C12 and MC(0 0 1) display a stronger resistance than M14C13. The presence of corner or edge sites in the M14C13 nanocrystal favors the formation of MoSxCy compounds. Following Sabatier's principle, our results suggest that flat MC(0 0 1) surfaces are too inert to catalyze HDS reactions, while M14C13 is too active to resist the sulfidation that leads to degradation of the carbides. For reactions involving sulfur and sulfur-containing molecules, nanoparticles adopting the special geometry of metcars should display a better catalytic activity than the corresponding bulk materials and carbide nanoparticles that have a cubic-based structure like nanocrystals. Indeed, DFT calculations indicate that Ti 8C12 and Mo8C12 are good catalysts for the HDS of thiophene.

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