Determination of the mechanism for ethylidyne formation from chemisorbed ethylene on transition-metal surfaces
- Univ. of California, Riverside (USA)
The effect of deuterium substitution has been studied in relation with the conversion of chemisorbed ethylene to ethylidyne on Pt(111). Thermal desorption (TDS) experiments with a 3:1 C{sub 2}D{sub 4}:C{sub 2}H{sub 4} mixture yielded traces for H{sub 2}, HD, and D{sub 2} that resemble those obtained with pure C{sub 2}H{sub 4} or C{sub 2}D{sub 4}, indicating that the reaction is intramolecular. Additional TDS using CHD=CD{sub 2} resulted in an enhanced H{sub 2} desorption at the expense of D{sub 2} for the first desorption peak, which is associated with the ethylidyne formation. Our recent kinetic data indicate that the reaction rate for ethylidyne formation displays first-order dependence on ethylene coverage and a normal isotope effect upon deuterium substitution. The TDS results with CHD=CD{sub 2} then prove that the hydrogen atom involved in the slow step for ethylene conversion is the same that desorbs from the surface first, so a mechanism that invokes ethylidene (S=CH-CH{sub 3}, S = surface) as an intermediate can be discounted. We propose the formation of vinyl (S-CH=CH{sub 2}) fragments instead.
- OSTI ID:
- 6971262
- Journal Information:
- Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:12; ISSN 0002-7863; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360104 -- Metals & Alloys-- Physical Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000 -- Chemistry
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKENES
CHEMICAL REACTIONS
CHEMISORPTION
DATA
DATA ANALYSIS
DEUTERIUM
ELEMENTS
ETHYLENE
EXPERIMENTAL DATA
HYDROCARBONS
HYDROGEN ISOTOPES
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MEASURING INSTRUMENTS
MEASURING METHODS
METALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PLATINUM
PLATINUM METALS
SEPARATION PROCESSES
SORPTION
STABLE ISOTOPES
SURFACE PROPERTIES
TRANSITION ELEMENTS