Scanning tunneling microscopy and scanning tunneling spectroscopy studies of powdery palladium/graphite model catalysts
Powdery Pd/graphite model catalysts were studied with transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS), with the later two techniques in air. In contrast to TEM images, STM/STS data are representative of the very surface and are therefore more relevant for an interpretation of the catalytic properties of these kind of catalysts. Besides spherical clusters and layered structure, also platelike and diffuse structures could be distinguished in the STM images. An assignment of the different objects to one of the main elements-graphite and palladium-was possible with STS. The I(V) curves on graphite are always much narrower on the V axis than those on palladium, and their slope dI/dV is, thus, larger. Utilizing this distinction, chemical maps were determined by taking I(V) data over a grid of surface points and assigning each point the value of the integral under its dI/dV curve. The comparison of such a chemical map with the topographic STM picture of the same area shows that only the spherical cluster structures consist of palladium, in accordance with the TEM pictures. The layered and platelike structures are identified as graphite, and the diffuse structures probably belong to impurities. In any case, the latter consist neither of graphite nor of palladium. A statistical analysis of the cluster morphology reveals that at low Pd loads the clusters are of spherical shape whereas the average width-to-height ratio increases at higher concentrations. The clusters at higher Pd concentrations exhibit a more elliptical shape.
- Research Organization:
- Inst. fur Physikalische und Theoretische Chemie der Univ. Bonn (DE)
- OSTI ID:
- 20000517
- Report Number(s):
- CONF-9808111-; LANGD5
- Journal Information:
- Langmuir, Vol. 15, Issue 18; Conference: Third international symposium on effects of surface heterogeneity in adsorption and catalysis on solids, Torun (PL), 08/09/1998--08/16/1998; Other Information: PBD: 31 Aug 1999; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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