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.