Ti<sup>2+</sup> Site-Promoted N≡N Bond Activation in LaTiO<sub>3–<i>x</i></sub> Nanosheets for Nitrogen Photofixation
Mengyang Xia, Ben Chong, Xiangjiao Gong, Hang Xiao, He Li, Honghui Ou, Bin Zhang, Guidong Yang
Abstract
Using solar energy to fix N 2 and produce NH 3 is a promising route. For nitrogen photofixation, the transition-metal active site in the low oxidation state is conducive to the adsorption of N 2, but it is often difficult to further dissociate N 2, 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 LaTiO 3– x with an ultralow oxidation state Ti 2+ site is achieved via in situ modulation of phase transition and defect engineering. The obtained Ti 2+ sites could inject more d-orbital electrons into the N 2 π* antibonding orbitals to achieve N 2 activation and dissociation. Therefore, compared with pristine La 2 Ti 2 O 7 and La 2 Ti 2 O 7– x samples without ammonia production activity, LaTiO 3– x samples showed a remarkable performance for photocatalytic N 2 fixation. The NH 3 generation rate reached up to 107 μmol g cat –1 h –1 after the 1st hour, and the average NH 3 generation rate after 4 h was approximately 51.5 μmol g cat –1 h –1 . Furthermore, in situ characterization and density functional theory (DFT) calculations revealed the role of Ti sites with different oxidation states (Ti 4+, Ti 3+, Ti 2+ ) in N 2 activation, which would provide a unique perspective for designing efficient N 2 fixation catalysts.