Effects of elemental substitution on catalytic properties of Tsai-type 1/1 quasicrystal approximants for acetylene hydrogenation

Quasicrystals (QCs) and their approximant crystals (ACs) have many nonequivalent sites that can be controlled by elemental substitution and composition variation of the alloy system. This structural control at the crystallographic site level enables the design of material functions. QCs and ACs are expected to be applied as catalysts, with their catalytic properties depending on the local surface structure. Previously, we reported the excellent catalytic properties of Al-Pd-Sc Tsai-type 1/1 AC. In this study, we systematically investigated the effects of elemental substitution in various ternary Tsai-type 1/1 ACs—(Al,Ga,In)-(Pd,Pt)-(Sc,Tb,Dy,Ho)—on their catalytic behavior in acetylene hydrogenation. Substituting Ga or In with Al most effectively enhanced catalytic activity, whereas substitution among rare-earth elements had only a minor influence. Among all examined compositions, Al–Pd–Sc exhibited the highest activity, and all ACs showed high ethylene selectivity (>90%). Hard X-ray photoelectron spectroscopy and density functional theory (DFT) calculations were employed to elucidate the origin of these effects. The Pd 3d binding energy in Al–Pd–Sc shifted to higher values upon replacing Ga with Al, indicating that the electronic state of Pd can be tuned through elemental substitution and compositional control. DFT analysis further revealed that three types of nonequivalent sites contribute significantly to the reaction. These findings demonstrate that both the electronic structure and geometric configuration of active sites in Tsai-type ACs can be modulated through elemental substitution, highlighting the potential of ACs as structurally designable catalysts.