An in situ temperature dependent IR, EPR and high resolution XANES study on the NO=Cu þ –ZSM-5 interaction C. Prestipino a,b , G. Berlier a , F.X. Llabr es i Xamena a,c , G. Spoto a,c , S. Bordiga a,b,c , A. Zecchina a,c , G. Turnes Palomino d , T. Yamamoto e , C. Lamberti a,b,c, * a Dipartimento di Chimica IFM, Universit  a di Torino, Via Giuria 7, 10125 Torino, Italy b INFM UdR Torino Universit  a, Torino, Italy c INSTM UdR Torino Universit  a, Torino, Italy d Departamento de Qu  ımica, Universidad de las Islas Baleares, 07071 Palma de Mallorca, Spain e Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan Received 2 April 2002; in final form 23 July 2002 Abstract We report an in situ IR, EPR, and high resolution XANES study on the Cu þ ðNOÞ and Cu þ ðNOÞ 2 complexes formed at80KinCu þ –ZSM-5. Bare Cu 2þ ions (<1%) exhibit an axial EPR spectrum, while bare Cu þ ions exhibit well resolved 1s ! 4p xy and 1s ! 4p z transitions (p xy =p z splitting of 3.1 eV), reflecting the same local symmetry. Cu þ ðNOÞ complex exhibits an anisotropic EPR signal, while XANES spectrum of dinitrosyl adducts presents three resolved components ascribed to the 1s ! 4p x , 1s ! 4p y , and 1s ! 4p z transitions (p x =p y and p y =p z splitting of 3.8 and 2.6 eV, respectively) testifying the rupture of the axial symmetry of Cu þ bare cations upon NO adsorption. Upon increasing the temperature to 300 K, NO oxidizes a fraction of 75–85% of the cuprous ions. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction Copper-exchanged molecular sieves have been widely investigated after the discovery that copper exchanged ZSM-5 is active in the direct decom- position of NO [1–11]. Due to their superior cat- alytic activity, most of the data reported up to now refer to more than 100% copper-exchanged sam- ples 1 prepared via a conventional ion exchange procedure with aqueous solutions of cupric ions. These samples contain mixtures of copper ions in different aggregation and oxidation states [1–13]. The heterogeneity of copper species in catalysts prepared following that way makes the elucidation of structural and catalytic properties of isolated and clustered species a difficult subject. Since the 9 September 2002 Chemical Physics Letters 363 (2002) 389–396 www.elsevier.com/locate/cplett * Corresponding author. Fax: +39-011-670-7855. E-mail address: carlo.lamberti@unito.it (C. Lamberti). 1 Following the convention introduced by Iwamoto, a 100% exchange is reached when a Cu 2þ ion is introduced for each two monovalent counterions i.e., for each two Al 3þ ions of the framework. 0009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0009-2614(02)01183-1