Theoretical investigation of dinitrosyl complexes in Cu-zeolites as intermediates in deNOx process

Abstract

The structure and stability of nitrosyl complexes formed in Cu-FER zeolite were investigated using a periodic DFT model. The reliability of both DFT methods and cluster models when describing the Cu⁺ interaction with NO molecules was examined. The relative stabilities of mononitrosyl complexes on various Cu⁺ sites in Cu-FER are governed by the deformation energy of the particular site. Three types of dinitrosyl complexes with different coordination on the Cu⁺ cation were identified: (i) four-fold tetrahedral, (ii) four-fold square-planar and (iii) three-fold trigonal-planar complexes. The most stable dinitrosyl complex, formed when the two NO molecules interact with Cu⁺via the N atom, has a tetrahedral coordination on Cu⁺. The cyclic adsorption complex, having a square-planar arrangement of ligands on Cu⁺ and interaction viaO atoms, is only about 10 kJ mol⁻¹ less stable than the N-down dinitrosyl complex. This cyclic dinitrosyl complex is suggested to be the key intermediate in the deNO_x process taking place in Cu-zeolites.