The effect of hydrogen coadsorption on the thermal chemistry of methyl iodide on Ni(100) surfaces

Journal Article · Wed Dec 01 00:00:00 EST 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1339· OSTI ID:5258523

Tjandra, S; Zaera, F ^[1]

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1. Univ. of California, Riverside, CA (United States)

A detailed investigation of the surface chemistry of methyl iodide with preadsorbed hydrogen on Ni(100) is reported here. TPD data indicate that, in general, the presence of hydrogen on the surface induces a yield increase in methane formation and a reduction of the extent of which methyl species decompose as compared with the case where the methyl iodide is adsorbed by itself on a clean surface. Furthermore, two very different methane desorption regimes are observed at 150 and 220 K. By using both isotopically labelled methyl iodide and deuterium (D[sub 2] + CH[sub 3]I and H[sub 2] + CD[sub 3]I) it was determined that while the high-temperature methane is formed via the reductive elimination of surface methyl species produced by decomposition of methyl iodide with coadsorbed hydrogen atoms, the lower temperature methane TPD peak may be the result of a direct attack of the surface hydrogen on adsorbed methyl iodide molecules in a concerted fashion instead. The TPD data also indicate that neither methylene nor methylidyne intermediates form during the decomposition of methyl iodide on nickel below 200 K, and experiments with CH[sub 2]I[sub 2] clearly show that methylene species can be easily hydrogenated to methane in the presence of D[sub 2] coadsorption at quite low temperatures. Finally, no H-D exchange between methyl species and coadsorbed hydrogen (H[sub 2]) was observed. 44 refs., 20 figs.

• OSTI ID: 5258523
• Journal Information: Journal of Catalysis; (United States), Vol. 144:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
METHYL IODIDE
HYDROGENATION
NICKEL
CATALYTIC EFFECTS
CHEMICAL REACTION YIELD
DESORPTION
HYDROGEN
MILLER INDICES
REACTION INTERMEDIATES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
CHEMICAL REACTIONS
ELEMENTS
HALOGENATED ALIPHATIC HYDROCARBONS
IODINATED ALIPHATIC HYDROCARBONS
METALS
NONMETALS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
SORPTION
TEMPERATURE RANGE
TRANSITION ELEMENTS
YIELDS
400201* - Chemical & Physicochemical Properties