Single atom doping induced charge-specific distribution of Cu1-TiO2 for selective aniline oxidation via a new mechanism

Utilizing single atom sites doping into metal oxides to modulate their intrinsic active sites, achieving precise selectivity control in complex organic reactions, is a highly desirable yet challenging endeavor. Meanwhile, identifying the active site also represents a significant obstacle, primarily due to the intricate electronic environment of single atom site doped metal oxide. Herein, a single atom Cu doped TiO₂ catalyst (Cu₁-TiO₂) is prepared via a simple “colloid-acid treatment” strategy, which switches aniline oxidation selectivity of TiO₂ from azoxybenzene to nitrosobenzene, without using additives or changing solvent, while other metal or nonmetal doped TiO₂ did not possess. Comprehensive mechanistic investigations and DFT calculations unveil that Ti-O active site is responsible for triggering the aniline to form a new PhNOH intermediate, two PhNOH condense to azoxybenzene over TiO₂ catalyst. As for Cu₁-TiO₂, the charge-specific distribution between the isolated Cu and TiO₂ generates unique Cu₁-O-Ti hybridization structure with nine catalytic active sites, eight of them make PhNOH take place spontaneous dissociation to produce nitrosobenzene. This work not only unveils a new mechanistic pathway featuring the PhNOH intermediate in aniline oxidation for the first time but also presents a novel approach for constructing single-atom doped metal oxides and exploring their intricate active sites.