Atomic-Scale Engineering of CuO_x-Au Interfaces over AuCu Single-Nanoparticles

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Understanding interfacial structures in bimetallic nanoparticles is crucial for designing efficient catalysts.
• The behavior of copper in gold-copper (AuCu) alloy nanoparticles under oxidative conditions is not fully understood.
• Silica shells can stabilize and modify nanoparticle properties for catalytic applications.

Purpose of the Study:

• To investigate the effect of temperature on the interfacial structure of silica-coated AuCu nanoparticles.
• To correlate the interfacial structure and crystal phase with catalytic activity for CO oxidation.
• To elucidate the role of copper segregation and oxidation in modifying nanoparticle catalysis.

Main Methods:

• Synthesis of silica-coated AuCu nanoparticles (7.1 nm, 1:1 Au/Cu molar ratio, 6 nm silica shell).
• Annealing under oxidative atmosphere at temperatures ranging from 473 K to 773 K.
• Characterization of structural and chemical changes using advanced techniques (e.g., TEM, XPS - implied).
• Evaluation of catalytic activity for CO oxidation at 433 K.

Main Results:

• Copper atoms segregated and oxidized to form CuOₓ layers (up to 0.8 nm) on the AuCu particle surface with increasing temperature.
• The AuCu particle transformed from face-centered tetragonal (fct) to face-centered cubic (fcc) phase, with reduced size.
• Catalytic activity for CO oxidation decreased dramatically as temperature increased, particularly after the crystal phase transition.

Conclusions:

• The interfacial structure evolved from a CuOₓ monolayer on fct-AuCu to a thicker CuOₓ layer on fcc-Au/Au particles.
• The fct-AuCu/CuOₓ monolayer interface exhibited higher CO oxidation activity due to synergistic effects.
• The fcc-Au/Au/CuOₓ core-shell structure showed weakened interaction and significantly lower catalytic performance.