Why Single-Atom Alloys (SAAs) Outperform Their Individual Metal Components in Catalysis

gaps, using the selective hydrogenation of unsaturated aldehydes with Pt-Cu alloys as a prototypical system. We have determined that, in the very dilute limit, the Pt atoms are located not on the exposed NP surface but rather at the interface between the metal NP and the oxide support, where they are inaccessible to the reactants. Furthermore, their effect on catalytic performance was found to be indirect, via the remote modification of the electronic properties of the surface Cu atoms where the reactions take place. Specifically, the activation barrier for molecular hydrogen dissociation at the Cu sites is decreased, thereby facilitating the production of the atomic hydrogen required for the hydrogenation of the organic adsorbates. Moreover, the added Pt modifies both the adsorption mode and the energetics of the reactants and products on Cu sites and the rate constants of the hydrogenation steps; like pure Cu once it is provided with atomic hydrogen, the Cu-Pt SAAs enhance the production of the desired products (unsaturated alcohols from unsaturated aldehydes), likely by favoring a unique reactant adsorption geometry through the oxygen atom. Our findings contradict the proposed independence of the two metals that constitutes the essence of the current working model for SAA and provide a new explanation of how SAAs function that may lead to better formulations of new bimetallic catalysts.