Dynamic Metal-Support Interaction Dictates Cu Nanoparticle Sintering on Al₂O₃ Surfaces

Nanoparticle sintering remains a critical challenge in heterogeneous catalysis. In this work, we present a unified deep potential (DP) model based on the Perdew-Burke-Ernzerhof approximation of density functional theory for Cu nanoparticles on three Al₂O₃ surfaces (γ-Al₂O₃(100), γ-Al₂O₃(110), and α-Al₂O₃(0001)). Using DP-accelerated simulations, we reveal that the nanoparticle size-mobility relationship strongly depends on the supporting surface. The diffusion of nanoparticles on the two γ-Al₂O₃ surfaces is almost independent of the size of the nanoparticle, while the diffusion on α-Al₂O₃(0001) decreases rapidly with increasing size. Interestingly, nanoparticles with fewer than 55 atoms diffuse several times faster on α-Al₂O₃(0001) than on γ-Al₂O₃(100) at 800 K while expected to be more sluggish based on their larger binding energy at 0 K. The diffusion on α-Al₂O₃(0001) is facilitated by dynamic metal-support interaction (MSI), where Al atoms move out of the surface plane to optimize contact with the nanoparticle and relax back to the plane as the nanoparticle moves away. In contrast, the MSI on γ-Al₂O₃(100) and on γ-Al₂O₃(110) is dominated by more stable and directional Cu-O bonds, consistent with the limited diffusion observed on these surfaces. Our extended MD simulations provide insight into the sintering processes, showing that the dispersity of the nanoparticles strongly influences the coalescence driven by nanoparticle diffusion. We observed that the coalescence of Cu₁₃ nanoparticles on α-Al₂O₃(0001) can occur in a short time (10 ns) at 800 K even with an initial internanoparticle distance increased to 3 nm, while the coalescence on the two γ-Al₂O₃ surfaces are inhibited significantly by increasing the initial internanoparticle distance. These findings demonstrate that the dynamics of the supporting surface is crucial to understanding the sintering mechanism and offer guidance for designing sinter-resistant catalysts by engineering the support morphology.