Catalytic performance of La@Mg₁₂O₁₂ as a single atom catalyst toward nitrogen reduction reaction for ammonia...

The catalytic nitrogen reduction reaction (NRR) offers an ecofriendly pathway for ammonia production under ambient conditions, yet the high bond dissociation energy of the N ≡ N triple bond necessitates highly efficient catalysts. Single atom catalysis (SAC) has emerged as cost effective and efficient technique for facilitating NRR to ammonia (NH₃). Herein, density functional theory (DFT) calculations are implemented to investigate lanthanum doped magnesium oxide (La@Mg₁₂O₁₂) nanocage as SAC for efficient conversion of N₂ to NH₃. The calculated interaction energy (E_int. = -2.40 eV) and formation energy (-2.60 eV) reflect the thermodynamic stability of La@Mg₁₂O₁₂ complex. Non-covalent interaction (NCI), quantum theory of atoms in molecules (QTAIM) and Ab initio molecular dynamics (AIMD) simulations, further verified the strong and effective interaction between La and the Mg₁₂O₁₂ nanocage. The optimal NRR pathway happens via an end-on adsorption configuration of N₂ with Mg₁₂O₁₂ (E_int. = -0.64 eV), which is more stable than side on with interaction energies of -0.43 eV, respectively. The seventh Proton Coupled Electron transfer (PCET) step (NH₂∗ conversion to NH₃∗) is identified as the potential determining step, with an overpotential of 1.02 eV and a Gibb's free energy change of 1.59 eV. These values demonstrate that La@Mg₁₂O₁₂ is an efficient SAC for NRR and exhibits higher selectivity toward NRR than competing hydrogen evolution reaction (HER), for which the Volmer step has a Gibb's free energy of -0.68 eV. The Tafel step is the potential-determining step of HER process with overpotential of 0.92 eV. Overall, this work introduces La@Mg₁₂O₁₂ as a promising f-block SAC platform for efficient and environmentally friendly ammonia synthesis and for the rational designing of next generation NRR electrocatalysts.