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

Using solar energy to fix N-2 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 N-2, thus reducing the energy barrier of N-2 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 N-2 p* 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 N-2 fixation. The NH3 generation rate reached up to 107 mu mol g(cat)(-1) h(-1) after the 1st hour, and the average NH3 generation rate after 4 h was approximately 51.5 mu mol 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 N-2 activation, which would provide a unique perspective for designing efficient N-2 fixation catalysts.

Automated summary

This study successfully achieved LaTiO3-x samples with ultralow oxidation state Ti2+ sites through modulation of electron energy level of active sites. The obtained Ti2+ sites effectively activated N-2 and achieved NH3 generation, providing new insights for designing efficient N-2 fixation catalysts.