Activity and characterization of Pd thin films, microfabricated dots, and cluster based model catalysts

The use of various model catalysts' configurations is illustrated to study the relation between catalytic activity and surface structure. The hydrogen ation of 1,3-butadiene is used as a test reaction to correlate kinetic para meters with catalysts' properties. The first model catalysts studied were P d thin films. STM and XPS were used to characterize the catalyst and correl ate the effect of sulfur poisoning with catalytic activity. It was found th at the kinetic parameters depended on both the sulfur content and surface m orphology. It is speculated that morphological changes caused by sulfur rec onstruction change the distribution of active sites. The second model catal yst was a microfabricated catalyst consisting of a regular array of catalyt ic dots. Dots with different compositions were prepared to study the effect of Pd-Au alloys on activity. It was found that addition of gold decreased the activation energy and reduced the number of active sites by diluting th e surface. The third type of model catalysts studied are catalysts derived from molecular clusters of clusters which have a well defined structure and composition. Upon pyrolysis, these materials decompose and form self-suppo rted porous bimetallic catalysts. It was found that the activity and select ivity of these materials varied with the structure of the precursor as well as with the temperature used to decompose them. These type of model cataly sts provide a novel route to design new catalysts.