The electronic properties of palladium supported on SiO/sub 2/ and La/sub 2/O/sub 3/ were investigated by X-ray photoelectron spectroscopy. Spectra were collected after each stage of catalyst preparation: deposition of the palladium chloride precursor, oxidation in air at 623 K, and reduction in H/sub 2/ at 573 K. The Pd 3d/sub 5/2/ binding energies recorded following precursor deposition and oxidation were the same on both catalysts. However, after reduction the Pd 3d/sub 5/2/ binding energies of the Pd/La/sub 2/O/sub 3/ samples shifted below the corresponding values for metallic Pd, while the Pd 3d/sub 5/2/ binding energies of the Pd/SiO/sub 2/ samples did not. Furthermore, the binding energies for the Pd/La/sub 2/O/sub 3/ samples decreased with increasing metal loading, the largest Pd particles apparently exhibiting the greatest interaction. A maximum shift of -0.7 eV relative to the Pd foil value was observed for 8.8% Pd/La/sub 2/O/sub 3/. This binding energy shift is interpreted as arising from a change in the chemical state of Pd, i.e., that Pd supported on La/sub 2/O/sub 3/ is more electronegative than zero-valent Pd alone. A model is proposed which suggests that a thin covering of the La/sub 2/O/sub 3/ support lies on a portion of themore » Pd surface. The exact composition of the support depended strongly on the reduction temperature and the amount of Pd deposited. 49 references, 13 figures, 9 tables.« less
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