Unlocking the potential of alkaline-earth metal active centers for nitrogen activation and ammonia synthesis: the role of s–d orbital synergy

N 2 can be activated via s–d orbital synergy of AE metal active centers, i.e. , AE metals's orbitals share electrons with their empty d orbitals, and then the partially occupied d orbitals exchange electrons with the σ and π* orbitals of N 2 .