Substitution of Pd with Cu and Ag in InPd₃ intermetallics enhances net alkene selectivity in competitive acetylene hydrogenation

Intermetallic catalysts enable tuning semi-hydrogenation catalytic selectivity by modifying the geometric and/or electronic states of active sites. Herein, a series of Cu- and Ag-substituted TiAl₃-type InPd₃ intermetallics were synthesized to examine the impact of Pd substitution on acetylene semi-hydrogenation. The selective chemical substitution of Pd with coinage metals (Cu and/or Ag) in InPd₃ does not disrupt the configuration of surface Pd active sites (Pd stripes). Rather, Cu and Ag substitutions modify the electronic structure of these Pd sites. Competitive acetylene-propylene hydrogenation was employed to probe the effect of electronic modification on alkene selectivity. Density functional theory calculations corroborate experimental observations that Ag substitution exhibits higher net alkene selectivity than Cu substitution, owing to greater electronic modification of Pd actives sites. This work demonstrates the ability to decouple electronic effects from geometric effects in intermetallics used as selective hydrogenation catalysts.