Alkyl chain propagation by methylene insertion on Cu(100)
- Columbia Univ., New York, NY (United States)
One of the mechanisms proposed for formation of carbon-carbon bonds in the Fischer-Tropsch synthesis, the so-called carbon/methylene mechanism, involves the propagation of alkyl chains on the catalyst surface by methylene insertion. The studies reported here provide evidence for this reaction on single crystal copper surfaces under ultra-high vacuum conditions. Alkyl iodides are used as molecular precursors to generate adsorbed methylene and alkyl groups on a Cu(100) surface. High-resolution electron energy loss spectroscopy and work function change measurements show that C-I bond dissociation occurs below 200 K in iodoalkanes to form alkyl groups on the surface. Indirect evidence supports the formation of adsorbed methylene groups via CH[sub 2]I[sub 2] dissociation. Temperature-programmed reaction studies of the CH[sub 2] + CD[sub 3] reaction show that sequential CH[sub 2] insertion followed by [beta]-hydride elimination produces ethylene-d[sub 2] and propylene-d[sub 3]. Similarly, reaction of CH[sub 2] with C[sub 2]D[sub 5] produces propylene-d[sub 4]. All of these reactions are extremely facile, occurring at 230-250 K with activation energies of 12-20 kcal/mol. Similar studies on Cu(110) show that the methylene insertion reaction is structure sensitive, being approximately two orders of magnitude faster on Cu(100) than on Cu(110). The source of this difference appears to be slow diffusion of methylene across the corrugated Cu(110) surface. 42 refs., 15 figs., 1 tab.
- OSTI ID:
- 7185319
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 147:1; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
100200 -- Synthetic Fuels-- Production-- (1990-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ALKENES
CATALYSIS
CATALYTIC EFFECTS
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COPPER
DEUTERIUM COMPOUNDS
ELEMENTS
ENERGY
FISCHER-TROPSCH SYNTHESIS
HETEROGENEOUS CATALYSIS
HYDROCARBONS
HYDROGEN COMPOUNDS
METALS
MILLER INDICES
ORGANIC COMPOUNDS
SYNTHESIS
TRANSITION ELEMENTS