Substrate augmented catalytic activity towards NRR: A case study of Li doped Al clusters on defective graphene

Highlights: • Dinitrogen activation on Al_n-1Li (n = 3–13) nanoclusters with and without support is studied using DFT studies. • Aln-1Li (n = 3–13) nanoclusters showed maximum N-N elongated bond length of 1.4 Å corresponding to redshift of 1207 cm⁻¹ in case of Al₃Li cluster. • Subsequently, Al_n-1Li (n = 3–13) nanoclusters supported on C₃ defective graphene exhibit enhanced activity in terms of N₂ activation as compared to their bare counter parts. • This study validates why and how increased cluster size is corelated with increased activity and why specific clusters with a particular number of atoms are active when embedded on defective graphene using electronic parameters. • Present work demonstrates maximum N-N elongated bond length of 1.56 Å corresponding to redshift of 1690 cm⁻¹ in case of Al₇Li@graphene and Al₁₂Li@graphene complexes reported till date. Density Functional Theory (DFT) based methods are applied to examine the potential of lithium doped aluminium clusters consisting of 3–13 atoms for dinitrogen molecule activation in terms of NN bond length, redshift in NN bond stretching frequency, nitrogen interaction energy and frontier molecular orbitals analysis. The present work highlights the role of monovacant C₃ defective graphene as a support in fine tuning the catalytic activity of Li doped Al clusters for reduction of N₂. Fundamental insights to synergic binding of clusters with defective graphene is brought out and its role in enhancing activation of dinitrogen molecule is explained. Supported Al_n-1Li clusters with six or more atoms are noted to be more active towards N₂ molecule activation as compared to the clusters without support. Dinitrogen molecule undergoes a maximum bond elongation of 1.56 Å corresponding to redshift of 1690 cm⁻¹ on Al₇Li@graphene and Al₁₂Li@graphene. This is maximum value reported in context of activation for N₂ molecule till date.