Interaction of Hydrogen with Metal Sulfide Catalysts - Direct Observation of Spillover

Abstract

A combination of controlled-atmosphere electron microscopy and in-situ electron diffraction techniques have been used to study the manner by which certain metal sulfides interact with 0.2 Torr hydrogen. In these experiments single crystal graphite was used as a probe material since its reactivity in both molecular and atomic hydrogen is well characterized. When the metal sulfide was in direct contact or physically separated from the graphite probe, pitting of the basal plane regions was observed even at room temperature. This unusual behavior is believed to result from the action of atomic hydrogen which is produced via reversible dissociation of molecular hydrogen on the metal sulfide particles. These species are extremely reactive towards the π-electrons present on the graphite basal planes and this action leads to the creation of pits. At the low pressures used in this work, it is clear that the atomic species can migrate not only by surface diffusion processes (spillover) but also by transport through the gas phase.