Breaking Scaling Relations for Selective N -Phenylhydroxylamine Synthesis on Platinum Catalysts via Oxophilic Metal Alloying-Induced Asymmetric Adsorption of −NO 2

In the cascade hydrogenation reaction of nitroarenes to hydroxylamines, followed by the conversion of hydroxylamines to anilines, overcoming the hydroxylamine selectivity–activity trade-off imposed by the linear scaling relations remains challenging. Here, alloying Pt with an oxophilic metal (OM) (e.g., Fe, Co, and Ni) can disrupt such linear scaling relations, enabling high hydroxylamine yields without the additives typically required by conventional catalysts. Using Pt3Co/AC as a primary model, experimental and density functional theory (DFT) calculations demonstrate that the high performance in nitroarene reduction to hydroxylamine is ascribed to the asymmetric adsorption of the −NO2 group, i.e., one N–O bond binds at Pt sites and the other at Co, which spatially decouples cleavage of the initial N–O bond from subsequent desorption/hydrogenation of N–O-containing intermediates, thereby disrupting the linear scaling relation between nitrobenzene and N-phenylhydroxylamine (N-PHA). On Pt sites, cleavage of the first N–O bond in −NO2 (rate-determining step) proceeds with a reduced barrier. In contrast, hydrogenation of N-PHA on Co is kinetically less favorable than its desorption. Collectively, these effects yield high N-PHA selectivity without loss of activity. A similar trend was observed for PtFe/AC and PtNi/AC, both of which exhibit better performance than their Pt/AC counterpart.