Decoding structure-selectivity interplay in Pd-Ag nanocatalysts for butadiene semi-hydrogenation

Precise control over product selectivity in heterogeneous catalysis remains a key challenge due to the complex interplay of structural and electronic factors. Here, we demonstrate delicate tuning of product distribution in 1,3-butadiene semi-hydrogenation by engineering the size and composition of Pd-Ag nanostructures. By systematically decoupling size and electronic effects, we identify critical selectivity descriptors and establish structure-selectivity correlations across both monometallic and bimetallic series. The thresholds of ensemble size and Pd valence state for the formation of distinct products are experimentally determined. Integrating kinetic analysis, chemisorption studies, and density functional theory calculations, we show that increased ensemble size and Ag incorporation weaken 1-butene binding and elevate hydrogenation barriers, enabling selective formation of 1-butene (up to 66%) over thermodynamically favored 2-butenes. These insights reveal the fundamental roles of geometric and electronic modulation in governing selectivity and offer a generalizable framework for the rational design of multifunctional bimetallic catalysts.