III International Conference

PP-I-83DENSITY FUNCTIONAL THEORY MOLECULAR CLUSTER STUDY OF COPPERINTERACTION WITH NITRIC OXIDE DIMER IN Cu-ZSM-5 CATALYSTSZakharov I. 1, 2 , Ismagilov Z. 1 , Ruzankin S. 1 , Anufrienko V. 1 , Yashnik S. 1 , Zakharova O. 11 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Severodonetsk Technological Institute of Volodymyr Dal East Ukrainian NationalUniversity, Severodonetsk 93400, UkraineE-mail: zvonu@rambler.ruThe various quantum chemical models of catalytic active site in Cu-ZSM-5 zeolites areanalyzed. The density function theory (DFT) is used to calculate the electronic structure ofmolecular cluster (HO) 3 Al-O-Cu-O-Cu modeling the catalytic active site in Cu-ZSM-5zeolites and study the interaction and decomposition of NO. It is assumed that the ratedeterminingstage of the low-temperature selective catalytic reduction of NO is the formationof the π-radical (N 2 O 2 ) - on electron donor sites of Cu-ZSM-5 catalysts.After discovery of direct NO decomposition and selective catalytic reduction (SCR) ofNO by hydrocarbons over Cu-ZSM-5 zeolites, the interest in catalytic active sites of Cu-ZSM-5 and in activated forms of adsorbed NO grew considerably. Stabilization of isolatedCu 2+ and Cu + ions, as well as oxide CuO- and Cu 2 O-like clusters, [Cu-O-Cu] 2+ and bis-[Cu-μ-(O) 2 -Cu] 2+ dimers, and (-Cu-O-Cu-O-) chain structures in Cu-ZSM-5 has been observed byspectroscopic methods. These copper states each have been suggested to act as catalytic activesites in NO decomposition and SCR by hydrocarbons.We have observed isolated Cu 2+ ions in zeolite cation-exchange positions, copper oxidechain structures in the zeolite channels, and square-plain oxide clusters by electron spinresonance (ESR) and diffuse reflectance spectroscopy [1,2]. The most interesting among theabove states of copper ions are chain structures Cu 2+ —O 2- — Cu 2+ —O 2- — because of theeasiness of copper reduction and reoxidation in them as well the ability to stabilize bondedstates of copper ions with mixed valence Cu 2+···Cu + .Together with high electron affinity of the molecular dimer ONNO (E a = -1.3 ÷ -1.7 eV),this may result in the formation of surface anion π-radical (ONNO) - in such systems that issimilar to the organo-zirconium surface complex with (N 2 O 2 ) - observed by ESR [3].On the other hand, the formation of a strong bond between nitrogen atoms in such radical(N-N = 1.4Å) clearly indicates that decomposition of the intermediate form — (N 2 O 2 ) - to aN 2 O molecule and — (O) - is the preferred decomposition pathway. Indeed, the ONNO dimeradsorbed on the metal surface Ag(111) shows a surprising low-temperature reactivityproducing directly N 2 O adsorbed molecules with a low activation energy of 2.0 kcal/mol:155