Alkane adsorption dynamics on platinum single crystal surfaces

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7273936

McMaster, M C

The initial dissociation probability of methane and ethane was measured as a function of translational energy, polar angle, azimuthal angle, vibrational energy in excited states and surface temperature. Results for direct dissociation on both surfaces suggest an alkane activation mechanism involving direct cleavage of a C-H bond via the quantum mechanical tunneling of an H atom through the barrier to dissociation. Surface phonons and vibrational motion excited in these experiments do not significantly promote direct alkane dissociation under the experimental conditions used in these studies. Direct alkane dissociation on both platinum single crystal surfaces appears to be promoted by translational motion directed normal to (111) microstructure. The molecular adsorption probability of propane was measured as a function of translational energy, polar angle, azimuthal angle and surface temperature of 95 K. The adsorption probability on both surfaces decreases with increasing translational energy indicative of a non-activated adsorption process. The adsorption probability increases as the surface coverage increases due to better translational energy dissipation on the covered surface. The parallel momentum component participates in the adsorption process on the clean and propane-covered surfaces and becomes more important as the coverage increases due to increased corrugation in the propane adlayer. Finally, at coverages near monolayer saturation spontaneous desorption is observed in the direct adsorption probability experiments which were attributed to the occurrence of a phase transition in the propane adlayer that decreases the propane binding energy.

• Research Organization: Stanford Univ., CA (United States)
• OSTI ID: 7273936
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400200* -- Inorganic
Organic
& Physical Chemistry
ADSORPTION
ALKANES
CHEMICAL REACTION KINETICS
CRYSTALS
DISSOCIATION
ELEMENTS
HYDROCARBONS
KINETICS
METALS
MONOCRYSTALS
ORGANIC COMPOUNDS
PLATINUM
PLATINUM METALS
REACTION KINETICS
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES
TRANSITION ELEMENTS