Reactions of neopentane, methylcyclohexane, and 3,3-dimethylpentane on tungsten carbides: the effect of surface oxygen on reaction pathways

Journal Article · Mon Jul 01 04:00:00 EDT 1991 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(91)90094-K· OSTI ID:5529831

Ribeiro, F H; Betta, R A.D.; Boudart, M; Baumgartner, J; Iglesia, E ^[1]

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1. Stanford Univ., CA (USA) Exxon Research and Engineering Co., Annondale, NJ (USA)

High surface area tungsten carbides with WC and {beta}-W{sub 2}C structure were prepared by direct carburization of WO{sub 3} in CH{sub 4}-H{sub 2} mixtures. Their surfaces appear devoid of excess polymeric carbon and adsorb between 0.2 and 0.4 monolayers of CO and H. These materials are very active in neopentane hydrogenolysis. Chemisorbed oxygen inhibits hydrogenolysis reactions and leads to the appearance of isopentane among the reaction products. Neopentane isomerization to isopentane occurs only on Pt, Ir, and Au surfaces. Thus, oxygen-exposed tungsten carbides catalyze reactions characteristic of noble metal catalysts. 3,3-Dimethylpentane isomerizes much faster than neopentane on oxygen-exposed carbides; the isomer distribution suggests that isomerization proceeds via a methyl shift mechanism rather than through the C{sub 5}-ring hydrogenolysis pathways characteristic of highly dispersed Pt. The apparent involvement of 3,3-dimethyl-1-pentene reactive intermediates is consistent with carbenium-type methyl shift pathways. Secondary carbon atoms, capable of forming stable carbenium ions, are present in 3,3-dimethylpentane but not in neopentane; they account for the high 3,3-dimethylpentane isomerization rate and selectivity on oxygen-exposed tungsten carbide-powders. Both dehydrogenation and isomerization reactions of methylcyclohexane occur on these carbide powders. These results suggest the presence of a bifunctional surface that catalyzes dehydrogenation and carbenium ion reactions typically occurring on reforming catalysts. 47 refs.

• DOE Contract Number: FG03-87ER13762
• OSTI ID: 5529831
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 130:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400* -- Petroleum-- Processing
ALKANES
CARBIDES
CARBON COMPOUNDS
CARBURIZATION
CATALYSTS
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
CYCLOALKANES
CYCLOHEXANE
DEHYDROGENATION
ELEMENTS
GOLD
HARDENING
HYDROCARBONS
IRIDIUM
ISOMERIZATION
KINETICS
METALS
NONMETALS
ORGANIC COMPOUNDS
OXYGEN
PENTANE
PLATINUM
PLATINUM METALS
REACTION INTERMEDIATES
REACTION KINETICS
REFORMER PROCESSES
REFRACTORY METAL COMPOUNDS
SEPARATION PROCESSES
SORPTION
SORPTIVE PROPERTIES
SURFACE AREA
SURFACE HARDENING
SURFACE PROPERTIES
SURFACE TREATMENTS
SYNTHESIS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TUNGSTEN CARBIDES
TUNGSTEN COMPOUNDS