Composition-Dependent Near-Surface Structure of High-Entropy Alloy Catalysts for the Semihydrogenation of Alkynes

Abstract

High-entropy alloys (HEAs) have drawn intensive interest in catalysis owing to their uniquely structured metal sites. However, the composition-dependent near-surface structure of HEAs, which is critical for regulating surface electronic structure and property, still remains unclear. Herein we reported a feasible wet-chemical strategy to synthesize quinary Pd x FeCoNiCu (Pd x -HEA) nanocrystals, which enabled the flexible control of Pd content (x = 2–27%) and the resultant tunable phase structure and size. The lattice expansion near surface increased with increasing heavy Pd atoms in Pd x -HEAs, which were quantitatively unveiled by aberration-corrected transmission electron microscopy. The semihydrogenation performance of alkynes to alkenes had a “volcano” plot in the dependence of Pd content in Pd x -HEAs. Among them, the Pd21-HEA catalyst exhibited the best performance for a series of alkynes, which was ascribed to the uniquely surrounding electronic environment around Pd induced by the strongest interaction (i.e., maximum electron transfer) between Co/Ni and Cu/Pd. This work demonstrated the importance of HEA composition-dependent lattice strain and the resultant surrounding electronic environment of Pd sites on the highly selective semihydrogenation.

Unveiling Atomic-Scaled Local Chemical Order of High-Entropy Intermetallic Catalyst for Alkyl-Substitution-Dependent Alkyne Semihydrogenation

“…Beyond that, how substituents on alkynes affect the catalytic hydrogenation is not well understood . It is therefore essential to understand and design the surface/subsurface − of catalysts, which undoubtedly plays a central role in regulating catalytic performance. Researchers have long been thinking about using intermetallic catalysts with ordered structures to regulate activity and selectivity simultaneously, which have attracted considerable attention in catalysis and controlled synthesis of nanomaterials due to their unique geometric and electronic structures. − There is also enormous potential in adjusting multiple active sites via the cocktail effect by designing high-entropy intermetallic (HEI) composed of multiple elements. − …”