Photoelectron spectroscopy of polycrystalline platinum catalysts

Abstract

Pt black catalysts have been characterized by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The spectra measured after standard purification (O₂ and H₂ at 600 K) compared well with those of a purified reference Pt foil. All samples exhibited pronounced Fermi-edge intensities in UPS although only 60–70% Pt was detected on their surfaces by XPS, the remainder being C and O. Line analysis of the C 1s XPS, region showed the presence of partly oxidized graphite and hydrocarbon polymer, likely in three-dimensional islands. OH/H₂O species attached to the metallic Pt sites were detected by UPS bands, in agreement with O 1s XPS line analysis. Similar spectral features are recorded at 600 K. Carbon could not be removed entirely by O₂ up to 850 K; hydrogen did not remove surface oxygen even up to 750 K. UPS features of C on Pt used in hydrocarbon reactions were similar to those reported for amorphous hydrogenated carbon overlayers. Consequences of the present findings for the catalytic properties of Pt in n-hexane reactions and the quantification of H₂–O₂ titration are discussed briefly.