Adsorptive separation based on porous materials is particularly promising for selective N-2 capture from natural gas. In this work, we proposed to achieve preferred N-2 adsorption by incorporating transition-metal cations into porous materials. Specifically, various porous-aromatic frameworks (PAFs) (PAF-302, PAF-303, and PAF-304) with transition-metal alkoxide ligands were constructed by incorporating transition-metal cations (Sc to Zn) on ligands. Quantum mechanics (QM) calculations indicated that the interactions of transition-metal-modified linkers with N-2 are higher than those with CH4, owing to the lack of pi* orbitals in CH4. Grand canonical Monte Carlo (GCMC) simulations show that Sc-, Ti-, V-, Cr-, Fe-, and Cu-functionalized PAFs exhibit high N-2/CH4 selectivity coefficients and high N-2 delivery amounts, especially in Sc- and Cu-functionalized PAFs. Therefore, incorporating transition metals into porous materials provides an efficient approach for highly efficient selective N-2 capture from natural gas.