STATIC CHARGE CORRECTION IN XPS ON CU-ZN-AL OXIDE CATALYST PRECURSORS WITH THE HELP OF DEPOSITED PD PARTICLES AS A REFERENCE MATERIAL

To obtain binding energy (BE) data from a photoelectron spectroscopy experiment (XPS) with poorly conductive samples, one needs a reliable inner BE reference. The problem of an inner static charge reference for Cu-Zn-Al oxide catalysts is studied on different samples including ZnO, defined hydroxycarbonates, precipitated precursors and calcined catalysts. With the help of an external reference material, i.e. deposited 20 +/- 10 nm Pd particles, the suitability of the C 1s, Zn 2p3/2 and Al 2s spectra to provide an inner static charge reference is tested. The Zn2+ 2p3/2 BE may serve as a reference when thoroughly calcined samples are exclusively investigated. Provided the Cu/Al surface concentration ratio is not to high, the Al 2s BE can be used in case of many calcined and precipitated samples when some care is taken. Considering C 1s BE related charge correction high systematic errors may occur due to the complexity of the C 1s spectra together with the known C 1s BE variation based on extra-atomic relaxation between the substrate and the contaminant hydrocarbon adsorbate.