Scanning probe microscopy of the activation and sulfur deactivation of Pd model catalysts

Abstract

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are used to image the microstructure of surfaces before and after pretreatment and reaction to establish a correlation between activity/deactivation and morphology. Several surfaces of flat thin Pd films supported on graphite, and single crystals of silica and alumina, show that the morphology of these films is highly sensitive to the method of activating the Pd catalysts. It is shown that the activity and selectivity for the probe reaction, butadiene hydrogenation, of a Pd/graphite film catalyst changes with the film microstructure. It is also shown that catalysts prepared via different procedures leading to the same surface structures exhibited the same reactivity, and vice versa, i.e. different microstrcutures lead to different activity, thus demonstrating a correlation between activity and morphology. The structure can be changed by changing the hydrocarbon to hydrogen ratio which causes significant deactivation due to changes in morphology.