Amorphous‐to‐Crystalline Transformation for Tunable Synthesis of Single Atom, Cluster, and Nanoparticle Catalysts: Dispersion of Metal Elements (Cu, Co, Ni, Y, Cs) on Holey 2D Ultra‐Thin Al2O3 Nanosheets

Herein, a versatile amorphous-to-crystalline transformation (ACT) strategy is described, to furnish various metals (Cu, Co, Ni, Cs, and Y) based atomically dispersed catalysts (ADCs) on thin holey 2D Al2O3. This approach, which involves adjusting reactant stoichiometry, enables the continuous modulation of particle size of ADCs at an atomical level, giving the ultrafine products as single atom, cluster, or nanoparticle catalysts. This synthesis method allows a straightforward analysis and comparison of the reactivity of the ADCs catalysts based on the dispersion of the active metal. In the case of Cu, the cluster catalyst 0.2-Cu/Al2O3 outperforms the single atom catalyst 0.1-Cu/Al2O3 and the nanoparticle catalyst 0.3-Cu/Al2O3 in the oxidation of refractory organic molecules, thanks to its superior electron transport and surface adsorption properties. These findings are well supported by the Density functional theory (DFT) calculations. Additionally, this method facilitates the preparation of atomic clusters with a very small size of 0.5-1 nm, composed of just a few atoms, as exemplified by Ni-based ADCs. The developed synthesis enriches the library of ADCs and demonstrates the potential of amorphous-to-crystalline transformation in creating advanced ultrasmall functional materials.