Auger spectroscopic study of the poisoning of a commercial palladium-alumina hydrogenation catalyst

Abstract

A commercial palladium-alumina catalyst used for the selective hydrogenation of diolefins in an olefin-aromatic-paraffin stream had lost most of its hydrogenation activity. It was examined by Auger electron spectroscopy after other typical physical measurements on the spent catalyst had failed to clearly establish the cause or causes of catalyst deactivation. Surface areas and levels of S and Cl in the fresh and the spent catalysts were not significantly different. However, iron to the extent of 1.7% by weight was found on the spent catalyst. This level of iron on a ~200 m 2/g surface area support is not necessarily a poison. However, Auger surface analysis has now revealed that iron was coating a majority of the palladium catalyst surface thereby masking (and poisoning) the active Pd surface atoms as well as the atoms of the promoters like Cr and Mo. The iron deposited on the catalyst came from a bad batch of feedstock. The surface analysis by Auger electron spectroscopy also revealed substantial amounts of surface Ca and large gradients of Pd, Cr, and Mo, from the outside to the inside of the pellets. The spent catalyst also had much higher amounts of iron on the outside than the interior surface of the catalyst pellets.