(160b) Overlayer Catalysts: Convincing Ourselves That the Observed Change Is Real

The binding strength of the catalyst on the products or reactants defines the success of a catalyst. The catalyst needs to bind the reactant and product strong enough to facilitate the desired reaction but not so strongly as to result in an undesired reaction or to poison the surface. Catalyst/species binding is controlled through the strain (distance) and ligand (electronic) properties of the metal. The periodic table provides a variety of element choices for catalytic application.

From an engineering perspective, the properties of certain metals for specific reactions are good, but improved performance is desired. A catalysts can facilitate a reaction of interest but a product or reactant might bind stronger than desired and block active sites. Overlayer bimetallic catalysts offer an opportunity to meet this binding strength challenge using a systematic approach. Overlayer (core@shell) can change the electronics of the overlayer and increase or decrease the binding strength depending on the choice of core metal. We have synthesized a series of bimetallic overlayer core@shell catalysts to investigate the ability of overlayer catalysts to improve reactivity when product and reactant binding issues are known to limit activity.

As we have worked on synthesizing, characterizing, and examining the reactivity of the bimetallic overlayer catalysts, we have also been repeatedly asking ourselves: how do we know this is real? What experiments can we perform that will demonstrate that the overlayer effect is real and not just something happening by chance? Repeatedly the answer has been to simply synthesize, characterize, and examine the reactivity of co-impregnated bimetallic catalysts. On multiple occasions, this simple approach has been very useful in providing experimental evidence that the bimetallic overlayer catalyst effect was real and not simply a random effect.