Hydrocarbon reactions on supported iridium catalysts

Journal Article · Mon Oct 15 00:00:00 EDT 1979 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/S0021-9517(79)80002-0· OSTI ID:5803092

Foger, K; Anderson, J R

The reactions of ethane, n-butane, isobutane, neopentane, neohexane, 2,3-dimethylbutane, and methylcyclopentane have been studied over a range of dispersed iridium catalysts in which the iridium was supported on ..gamma..-alumina or Aerosil silica, and d/sub Ir/ lay in the range less than or equal to 1 to 20 nm. The catalysts were characterized by electron microscopy, hydrogen adsorption, and temperature-programmed desorption of hydrogen. Hydrocarbon hydrogenolysis was the sole reaction pathway, except in the reaction of neopentane over catalysts with d/sub Ir/ of 7 and 20 nm, where some isomerization to isopentane was observed, and in the case of isobutane, where there was some inferential evidence for isomerization to n-butane prior to hydrogenolysis. The hydrocarbons fell into one of two classes depending upon the activation energy and the type of hydrogenolysis reaction occurring. Reaction in a C/sub 2/-unit mode (ethane the archetypal hydrocarbon) occurred with an activation energy in the region of 175 kJ Mol/sup -1/, and was the reaction mode for C/sub I/ - C/sub I/, C/sub I/ - C/sub II/, and C/sub II/ - C/sub II/ bond types. Reaction in an iso-unit mode (neopentane the archetypal hydrocarbon) occurred with an activation energy in the region of 235 kJ mol/sup -1/, and was the reaction mode for C/sub I/ - C/sub IV/, C/sub I/ - C/sub III/, and C/sub II/ - C/sub III/ bond types. (C/sub I/ indicates a primarycarbon, etc.) The activation energy and the frequency factor (expressed as rate per surface iridium atom) for reaction in the C/sub 2/-unit or the iso-unit mode was independent of d/sub Ir/. Provided the hydrogen pressure was kept sufficiently high, all reaction rates were proportional to P/sup 1//sub Hc/ P/sup -3//sub H/sub 2/. The reaction mechanism is discussed and is compared with the behavior of the corresponding reactions over platinum catalysts. 6 figures, 7 tables.

• Research Organization: Univ. of Melbourne, Parkville, Australia
• OSTI ID: 5803092
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 59:3; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

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ACTIVATION ENERGY
ADSORPTION
ALKANES
BUTANE
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CRYOGENIC FLUIDS
ELECTRON MICROSCOPY
ELEMENTS
ENERGY
ETHANE
FLUIDS
FREQUENCY DEPENDENCE
HYDROCARBONS
HYDROGEN
IRIDIUM
ISOMERIZATION
KINETICS
MECHANICAL STRUCTURES
METALS
MICROSCOPY
NONMETALS
ORGANIC COMPOUNDS
PLATINUM METALS
REACTION KINETICS
REFRACTORY METALS
SORPTION
SUPPORTS
TRANSITION ELEMENTS