The electronic nature of sites over Fe-ferrierite zeolite stabilizing active alpha-oxygen is analyzed by the periodic DFT + U approach. It is shown that two antiferromagnetically coupled Fe2+ cations with bridging OH-bonds form a stable bi-nuclear site of the [Fe2+< 2OH > Fe2+] doped FER complex. Frontier orbitals of this complex populated by two electrons with minority spins are localized in the bandgap. As a result, [Fe2+< 2OH > Fe2+] unit acquires the properties of a binuclear Lewis acid dipolarophile for 1,3-dipole N2O. First reaction step of N2O decomposition follows the Huisgen's concept of the 1,3-dipolar cycloaddition concept followed by the formation of reactive oxygen species Fe-O. (C) 2018 Elsevier B. V. All rights reserved.