Correlations between the surface structure of platinum single crystals and hydrocarbon skeletal rearrangement mechanisms: approach to the nature of the active sites
The isomerization and hydrocracking reactions of 2-methylpentane and n-hexane and the hydrogenolysis of methylcyclopentane were investigated on a clean Pt (311) single crystal at 350/sup 0/C under atmospheric pressure in an isolation cell housed within an ultrahigh vacuum chamber. The surface composition was monitored before and after the catalytic reactions by Auger electron spectroscopy. The results were compared with those obtained in the same experimental conditions on Pt (111), Pt (557), and Pt (119) surfaces, a polycrystalline foil, and two Pt/Al/sub 2/O/sub 3/ catalysts of both low and high dispersion. Experiments with labeled hexanes were also undertaken to determine the nature of the mechanisms involved in the isomerization reactions. The catalytic results show that each crystallographic face has its own peculiarities especially for (i) catalytic activity, (ii) selectivity as regards isomers produced, and (iii) selectivity as regards mechanisms. Conversely, the distribution of cracked products presents no significant structure sensitivity on massive metal surfaces although the highly dispersed alumina-supported platinum catalysts behave differently. Results with /sup 13/C-labeled hydrocarbons suggest that the atoms in the so-called B/sub 5/ site configuration are responsible for the bond-shift plus cracking reactions and that the atoms located at the corners and edges are involved in the cyclic mechanism.
- Research Organization:
- Universite Louis Pasteur, Strasbourg, France
- OSTI ID:
- 5451572
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 105:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400* -- Petroleum-- Processing
ALKANES
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ATMOSPHERIC PRESSURE
AUGER ELECTRON SPECTROSCOPY
CARBON 13
CARBON ISOTOPES
CATALYSIS
CATALYST SUPPORTS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CRACKING
CRYSTAL FACES
CYCLOALKANES
DECOMPOSITION
ELECTRON SPECTROSCOPY
ELEMENTS
EVEN-ODD NUCLEI
HEXANE
HYDROCARBONS
HYDROCRACKING
ISOMERIZATION
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGHT NUCLEI
METALS
NUCLEI
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM
PLATINUM METALS
PYROLYSIS
REACTION KINETICS
REFORMER PROCESSES
SPECTROSCOPY
STABLE ISOTOPES
SURFACE PROPERTIES
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENTS