Interactions of hydrogen with ethylene and ethane on iridium

Thesis/Dissertation · Wed Jun 01 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/7104391· OSTI ID:7104391

Mahaffy, Paul Robert ^[1]

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1. Iowa State Univ., Ames, IA (United States)

In an effort to determine the details of reaction mechanisms, kinetic parameters are obtained for the following two catalytic reactions, C₂Hsub>4+ Hsub>2 → Csub>2Hsub>6 and Csub>2Hsub>6+ Hsub>2 → 2 CHsub>4. The first reaction is carried out, for the most part, under reaction conditions (e.g. 110-200 K) which prevent complications caused by a side reaction, the surface dehydrogenation of adsorbed ethylene. The second reaction is carried out at somewhat higher temperatures (80 to 200°C). Both reactions are studied in the pressure range 0.5 to 1000 μ Extensive isotope labeling experiments are also carried out, which together with the kinetic measurements support in a self-consistent way the following mechanisms of hydrogen addition. The adsorbed species Csub>2Hsub>5(a) and H(a) are found to be intermediates in both the hydrogenation and hydrogenolysis reactions. In the case of the hydrogenation reaction, the rate limiting step is found to be the irreversible addition of an adsorbed hydrogen atom to an adsorbed ethylene molecule to produce Csub>2Hsub>5(a) which is further hydrogenated to produce ethane. The hydrogenolysis occurs by dissociative adsorption of ethane to produce Csub>2Hsub>5(a) and H(a). In this case the final kinetically significant elementary step is the reaction of an adsorbed hydrogen atom with one of the methyl hydrogen atoms of Csub>2Hsub>5(a), which produces a hydrogen molecule and is accompanied by the breaking of the carbon-carbon bond. Other processes which are kinetically significant for the hydrogenolysis reaction include slow (the sticking coefficient approximately 10^-5) ethane adsorption, slow ethane desorption (by reaction of Csub>2Hsub>5(a) with H(a)), the reversible dehydrogenation of Csub>2Hsub>5(a) to produce Csub>2Hsub>4(a) and competition of hydrogen for the surface sites on which the hydrocarbon species are adsorbed.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: US Energy Research and Development Administration (ERDA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 7104391
• Report Number(s): IS-T--758
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACTIVATION ENERGY
ALKANES
ALKENES
CATALYSTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CRYOGENIC FLUIDS
DEHYDROGENATION
ELEMENTS
ENERGY
ETHANE
ETHYLENE
FLUIDS
HYDROCARBONS
HYDROGEN
KINETICS
NONMETALS
ORGANIC COMPOUNDS
REACTION KINETICS