Surface structure and temperature dependence of n-hexane skeletal rearrangement reactions catalyzed over platinum single crystal surfaces: marked structure sensitivity of aromatization
The surface structure and temperature dependence of n-hexane skeletal rearrangement was investigated near atmospheric pressure and at 520-700 K over a series of five platinum single crystal surfaces with variable terrace, step, and kink structures. The atomic structure and surface composition of the active catalyst was determined before and after reactions using low energy electron diffraction and Auger electron spectroscopy. Aromatization of n-hexane to benzene displayed unique structure sensitivity in which the rates and specificity for this important reforming reaction were maximized on platinum surfaces with hexagonal (111) terrace structure. The rates of competing isomerization, C/sub 5/-cyclization, and hydrogenolysis reactions displayed little dependence on surface structure, although hydrogenolysis product distributions were influenced markedly by terrace structure. Platinum surfaces with (100) terraces favored internal C-C bond *scission, whereas surfaces with (111) terraces displayed high selectivity for terminal hydrogenolysis. Skeletal rearrangement was dominated by cyclic mechanisms involving both 1,5- and 1,6-ring closure. Marked variations in reaction selectivity with reaction conditions are related to a change of the most abundant surface intermediate that results from changes in the surface concentration of chemisorbed hydrogen. Catalyst deactivation resulted from the formation of disordered carbonaceous deposits on the platinum surfaces whose primary role was that of a nonselective poison. 19 figures, 5 tables.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5254686
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 85:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKANES
AROMATIZATION
ATMOSPHERIC PRESSURE
AUGER ELECTRON SPECTROSCOPY
CATALYSTS
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
CRYSTALS
DEHYDROCYCLIZATION
DIFFRACTION
ELECTRON DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
HEXANE
HIGH TEMPERATURE
HYDROCARBONS
HYDROGEN
ISOMERIZATION
METALS
MOLECULAR STRUCTURE
MONOCRYSTALS
NONMETALS
ORGANIC COMPOUNDS
PLATINUM
PLATINUM METALS
SCATTERING
SENSITIVITY
SEPARATION PROCESSES
SORPTION
SPECTROSCOPY
SURFACES
TRANSITION ELEMENTS