Effect of Particle Size and Alloying with Gallium and Zinc in Copper Nanoparticles from Ab Initio Molecular Dynamics

Abstract

Supported nanoparticles (NPs) are an intense field of research in industry and academia due to their unique catalytic properties. Yet, establishing relationships between structure and activity is challenging due to multiple possible compositions, interfaces, and alloy formation. This is especially pronounced for bimetallic NPs used in the CO₂-hydrogenation-to-methanol, where the structure responds dynamically to the chemical potential of the reactants and products, resulting in distinct surface structures depending on the exact reaction conditions. These phenomena have been highlighted by combining ab initio Molecular Dynamics (AIMD) and Metadynamics (MTD) with in situ X-ray absorption spectroscopy, chemisorption, and CO-IR. Here, we aim to understand how particle size and simulation temperature influence the structure and dynamics of small Cu NPs using the diffusion coefficients and the radial distribution function/atomic pair density function as descriptors using AIMD simulations. We found that decreasing the particle size or increasing the simulation temperature results in increased atom mobility, highlighted by the increased metal diffusion and resulting in reduced particle crystallinity. We also find that alloying Cu with Ga significantly increases the diffusion of both elements in the particle compared to the monometallic ones. In contrast, such diffusion lies in between the individual elements composing the CuZn particles.