Ti2+ Site-Promoted N≡N Bond Activation in LaTiO3–x Nanosheets for Nitrogen Photofixation

Using solar energy to fix N2 and produce NH3 is 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 N2 dissociation. Here, the perovskite-type LaTiO3–x with 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 N2 π* antibonding orbitals to achieve N2 activation and dissociation. Therefore, compared with pristine La2Ti2O7 and La2Ti2O7–x samples without ammonia production activity, LaTiO3–x samples showed a remarkable performance for photocatalytic N2 fixation. The NH3 generation rate reached up to 107 μmol gcat–1 h–1 after the 1st hour, and the average NH3 generation rate after 4 h was approximately 51.5 μmol gcat–1 h–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 N2 activation, which would provide a unique perspective for designing efficient N2 fixation catalysts.