Ti²⁺Site-Promoted NN Bond Activation in LaTiO_{3- x}Nanosheets for Nitrogen Photofixation

Using solar energy to fix N₂and produce NH₃is a promising route. For nitrogen photofixation, the transition-metal active site in the low oxidation state is conducive to the adsorption of N₂, but it is often difficult to further dissociate N₂, restricting the reaction. Therefore, it is necessary to precisely modulate the electron energy level of the active site to couple with the molecular orbitals of N₂, thus reducing the energy barrier of N₂dissociation. Here, the perovskite-type LaTiO_3-xwith an ultralow oxidation state Ti²⁺site is achieved via in situ modulation of phase transition and defect engineering. The obtained Ti²⁺sites could inject more d-orbital electrons into the N₂π∗ antibonding orbitals to achieve N₂activation and dissociation. Therefore, compared with pristine La₂Ti₂O₇and La₂Ti₂O_7-xsamples without ammonia production activity, LaTiO_3-xsamples showed a remarkable performance for photocatalytic N₂fixation. The NH₃generation rate reached up to 107 μmol g_cat^-1h^-1after the 1st hour, and the average NH₃generation rate after 4 h was approximately 51.5 μmol g_cat^-1h^-1. Furthermore, in situ characterization and density functional theory (DFT) calculations revealed the role of Ti sites with different oxidation states (Ti⁴⁺, Ti³⁺, Ti²⁺) in N₂activation, which would provide a unique perspective for designing efficient N₂fixation catalysts.