Chemical modification of surfaces: the effect of potassium on the chemisorption of molecules on transition metal crystal surfaces
The physical and chemical properties of pure potassium monolayers and its effect on the adsorption of oxygen, carbon monoxide and benzene on the (111) faces of platinum and rhodium single crystals are described. Potassium adsorption on both surfaces is quite similar. Potassium forms hexagonally close packed structures that are incommensurate with the substrate. The heat of desorption of potassium on these surfaces decreases with increasing potassium coverage. The surface free electron density increases and the work function decreases substantially wtih alkali adsorption, indicating charge transfer occurs from potassium to the substrate. Oxygen adsorption increases the potassium binding energy, and forms a surface complex at high potassium coverages. Oxygen adsorption is dissociative on both clean and potassium dosed Rh(111). The metal-oxygen stretching vibration increases in the presence of potassium, indicating stronger adsorption. Carbon monoxide adsorption on both metal surfaces is strongly affected. With increasing potassium coverage, the heat of desorption increases while the C-O stretching frequencies decrease. Also, substantial population shifts from the atop to the bridged site occur. Dissociation of CO is induced on Rh(111) by the presence of potassium. Benzene is found to be ..pi.. bonded oriented with the ring plane parallel to the surface with C/sub 3v/(sigma/sub d/) symmetry on both the clean and potassium dosed Rh(111) surfaces. Potassium reduces the heat of desorption of molecular benzene and induces a lower temperature pathway to decomposition. The major influence of potassium is to increase the surface electron density, which, for molecular adsorbates with low lying vacant orbitals of the correct symmetry, can lead to substantial changes in their bonding with the surface.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5306226
- Report Number(s):
- LBL-17223; ON: DE84008345
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BENZENE
CHEMISORPTION
CARBON MONOXIDE
OXYGEN
PLATINUM
SORPTIVE PROPERTIES
POTASSIUM
RHODIUM
DESORPTION
ALKALI METALS
AROMATICS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
HYDROCARBONS
METALS
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
SEPARATION PROCESSES
SORPTION
SURFACE PROPERTIES
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties