Selectivity Regulation in Au-Catalyzed Nitroaromatic Hydrogenation by Anchoring Single-Site Metal Oxide Promoters

Precise control of selectivity in hydrogenation reactions is a long-standing challenge. Surface decoration of nanocatalysts with transition-metal oxide nanoparticles (NPs) is an effective strategy to tailor the catalytic selectivity but generally at the expense of activity due to the blocking of active sites. Here, we report that constructing single-site metal oxide modifiers (NiO, CoO_x, or FeO_x) on supported Au NPs by atomic layer deposition (ALD) can regulate their catalytic selectivity for nitroaromatic hydrogenation. The coverage of single-site metal oxide can be precisely tuned by altering the number of ALD cycles. The Au/TiO₂ decorated with five cycles of NiO (Ni: 0.32 wt %) in the style of a single site can efficiently change the product selectivity from azo to azoxy compounds without significantly blocking the surface active sites. The density functional theory calculations indicate that the azoxybenzene bonded to the single-site NiO-decorated Au(111) with a larger adsorption energy, which inhibits the overhydrogenation of azoxybenzene and results in high azoxybenzene selectivity. Our work has demonstrated a general and efficient way to regulate the reaction selectivity of metal nanocatalysts by anchoring single-site metal oxide promoters.