Understanding Selective Hydrogenation of Phenylacetylene on PdAg Single Atom Alloy: DFT Insights on Molecule Size and Surface Ensemble Effects

Single atom alloys (SAA) have proven to be effective catalysts, offering customizable properties for diverse chemical processes. Various metal combinations are used in SAAs and Pd dispersed materials are frequently employed in catalyzing hydrogenation reactions. Herein, we explore the hydrogenation of phenylacetylene to styrene and ethylbenzene on PdAg SAA using density functional theory calculations. Our results show that while PdAg SAA does improve the activity of the host Ag towards hydrogenation, a dilute PdAg SAA surface with isolated Pd-atoms is not selective towards partial hydrogenation of phenylacetylene. Additionally, we investigate how the size of the reactant molecule, the size of the metal alloy ensemble, and a ligand effect impact the hydrogenation process. The SAA enhances the binding strengths of various organic adsorbates, although this effect diminishes as the adsorbate size increases. Our findings indicate the dilute PdAg exhibits selectivity towards hydrogenation of smaller molecules such acetylene due to its distinct adsorption geometry. The selective hydrogenation of phenylacetylene necessitates a surface Pd dimer ensemble. Our research highlights the importance of both reactant molecule size and surface configurations in SAA catalysts. This is particularly crucial when dealing with the adsorption of sizable organic molecules where the functional group can adopt different adsorption modes.