Methane conversion and Fischer-Tropsch catalysis over MoS sub 2 : Predictions and interpretations from molecular orbital theory

Journal Article · Fri Sep 01 04:00:00 EDT 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90141-3· OSTI ID:6960468

Anderson, A B; Yu, J ^[1]

---

1. Case Western Univ., Cleveland, OH (USA)

An atom superposition and electron delocalization molecular orbital study has been made of a variety of CH{sub n} and CO reactions over coordinatively unsaturated Mo{sup IV} edge cations in MoS{sub 2}. CH{sub 3}, formed by oxidative insertion of an edge Mo into a CH{sub 4} bond, is found to dehydrogenate easily by means of H transfer to an adjacent Mo. The process is activated by the formation of a strong double bond between CH{sub 2} and Mo. Coupling of 2 CH{sub 3}, CH{sub 3} + CH{sub 2}, and 2 CH{sub 2} are found to proceed with high barriers, a consequence of electron promotion to the Fermi level during C-C bond formation, yielding unstable C{sub 2} species. Coupling to strongly adsorbed ethylene proceeds with the lowest barrier, and if ethylene forms hydrogenation to ethane is possible, although ethane formation from 2 CH{sub 4} is thermodynamically forbidden so none of these CH{sub n} coupling schemes will be productive in the absence of stabilizing ancillary reactions. CO is found to bind relatively weakly to fivefold coordinated Mo and strongly to fourfold coordinated sites. In the presence of a second adjacent fourfold coordinated Mo, CO easily tilts to the di-{sigma} bridging orientation and dissociates with a low barrier. In the Fischer-Tropsch process hydrogenation to CH{sub 3}(a) and H{sub 2}O(g) is expected. CO is found to insert into the Mo-CH{sub 3} bond, as found by Klier and co-workers, with a low barrier, and subsequent hydrogenations to form C{sub 2}H{sub 6} + H{sub 2}O or CH{sub 3}CH{sub 2}OH are found to be favorable. It is proposed that the selectivity toward alcohol formation over alkali-doped MoS{sub 2} (the DOW process) may stem from the ability of the alkali cations to bond to O from the CO insertions process, thus blocking hydrogenation to H{sub 2}O, which would lead to alkane products.

• OSTI ID: 6960468
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 119:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010408* -- Coal
Lignite
& Peat-- C1 Processes-- (1987-)
ALKANES
ALKENES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DEHYDROGENATION
DISSOCIATION
ETHANE
ETHYLENE
FISCHER-TROPSCH SYNTHESIS
HYDROCARBONS
HYDROGEN COMPOUNDS
HYDROGEN TRANSFER
HYDROGENATION
KINETICS
METHANE
MOLECULAR ORBITAL METHOD
MOLYBDENUM COMPOUNDS
MOLYBDENUM SULFIDES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
REACTION INTERMEDIATES
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
WATER