DFT calculations of unpromoted and promoted MoS{sub 2}-based hydrodesulfurization catalysts

Journal Article · Fri Oct 01 04:00:00 EDT 1999 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2598· OSTI ID:20000962

Byskov, L S; Noerskov, J K; Clausen, B S; Topsoee, H

Self-consistent density functional theory (DFT) is used to study the structure and active sites in unpromoted and promoted MoS{sub 2}-based hydrodesulfurization (HDS) catalysts. A model consisting of single-layer MoS{sub 2} chains with and without promoter atoms located at the edges is used to represent the structures in the catalysts, and full relaxation is allowed to find the lowest energy configurations. The results show that the most favored edge structures deviate significantly from those considered in the literature and those expected from simple terminations of the bulk MoS{sub 2} structures. The calculations also show that the promoter atoms prefer to be located at the so-called sulfur-terminated ({bar 1}010) MoS{sub 2} edges. Although such structures have not been considered previously, it is found that they are in agreement with available structural information from Extended X-Ray Absorption Fine Structure (EXAFS) experiments. Since the creation of sulfur vacancies is believed to be the first step for many hydrotreating reactions, the energy required to remove sulfur from the different structures has also been calculated. Comparison with catalytic activity results for MoS{sub 2}, Co-Mo-S, Ni-Mo-S, and Fe-Mo-S structures shows that the highest HDS activity is obtained for the structures with the lowest metal sulfur binding energy, in general agreement with the bond energy model (BEM). A more detailed analysis of the sulfur bonding in promoted MoS{sub 2} structures based on a simple LCAO-type model explains the origin of the different promotional behaviors. Finally, the adsorption of hydrogen on the different structures is discussed. The authors find hydrogen adsorption at edge sulfur atoms to be strong, and suggest that the S-edge is partly covered by SH groups during catalysis.

• Research Organization: Technical Univ. of Denmark, Lyngby (DK)
• OSTI ID: 20000962
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
02 PETROLEUM
BINDING ENERGY
CATALYSTS
CATALYTIC EFFECTS
DESULFURIZATION
HYDROGEN
MOLECULAR MODELS
MOLYBDENUM SULFIDES
PROMOTERS
SORPTIVE PROPERTIES