Phase Engineering of Atomically Dispersed Fe-Doped Amorphous RuO_x Nanosheets via Amorphous-Amorphous Transition for Oxygen Activation

Amorphous nanomaterials with identical compositions can possess distinct atomic structures, which significantly influence their performance, underscoring the importance of phase engineering in amorphous nanomaterials. However, the high Gibbs free energy and complex structures associated with their disordered atomic arrangements pose a significant challenge to the phase engineering of amorphous nanomaterials. Herein, we achieved phase engineering of atomically dispersed Fe-doped amorphous RuO_x nanosheets (A-Fe₁/RuO_x NSs) through amorphous-amorphous transition strategies. Specifically, as confirmed by X-ray absorption fine structure measurements, the Fe coordination environment in A-Fe₁/RuO_x NSs was regulated from FeO₄ tetrahedral to FeO₆ octahedral, driven by amorphous-amorphous transition, resulting in two distinct Ru-Fe pair configurations of A-Fe₁/RuO_x NSs: one with a connected tetrahedral FeO₄-octahedral RuO₆ configuration and the other one with a connected octahedral FeO₆-octahedral RuO₆ configuration. Density functional theory calculations demonstrated that the structure differences of the Ru-Fe pair efficiently regulated the adsorption mode of the O₂ molecules from top adsorption to bridge adsorption on an amorphous surface. Consequently, the A-Fe₁/RuO_x NSs with a connected tetrahedral FeO₄-octahedral RuO₆ configuration exhibited an enhanced formation of superoxide radicals during oxidative dehydrogenation reactions, resulting in remarkable catalytic activity in the synthesis of indole, indole derivatives, and quinoline.