Dynamic Fluxionality of Nickel Clusters Bypasses Linear Scaling Relations in Methane Dry Reforming

While oxide-supported Ni-cluster catalysts are highly active and stable for dry reforming of methane, the size-dependent role of metal-support interactions remains elusive. Here, we deploy a comprehensive framework-integrating density functional theory (DFT), Ab initio molecular dynamics (AIMD), and microkinetic modeling-to elucidate the structure-dynamic-reactivity relationship of six Ni clusters (Ni1 to Ni16) under realistic reaction conditions. DFT reveals that increasing cluster size enhances supportto-metal electron transfer and induces electronic segregation, ultimately driving the formation of robust bifunctional interfacial sites. Furthermore, AIMD simulations indicate that while larger clusters maintain structural rigidity, medium-sized clusters exhibit dynamic fluxionality, reconstructing into highly active, transient single-atom-like configurations at elevated temperatures. Using carbon (EC) and hydrogen (EH) adsorption energies as descriptors, the microkinetic models yield distinct volcano plots for CO and H2 formation revealing a fundamental decoupling in their electronic requirements. Coverage analysis highlights a pronounced size effect: mechanistic shift: small clusters are thermodynamically quenched by oxygen poisoning, whereas large clusters are kinetically bottlenecked by inefficient H-H coupling. Ultimately, the Ni8 configuration achieves an optimal balance between these competing constraints, demonstrating that leveraging dynamic fluxionality and cluster nuclearity offers a powerful strategy to bypass static scaling relations in complex reforming reactions.