Co-adsorption NO and organic molecules on Cu + sites in zeolites: Quantum chemical DFT calculations P. Kozyra * , J. Datka Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Krako ´ w, Poland Received 10 November 2005; received in revised form 20 April 2006; accepted 21 June 2006 Available online 1 July 2006 Abstract The co-adsorption of organic molecules: acetone, formaldehyde, ethene and acetylene together with NO on the same Cu + site in zeo- lite CuZSM-5 was investigated by DFT calculations. The aim of this study was to follow the effect of NO on activation of multiple bonds in organic molecules and the effect of organic molecules on the activation of N@O bond. The extent of activation of C@O, C@C, C„C as well as of N@O bonds was characterized by the result of calculation as the elongation of the multiple bonds, decrease of bond order as the decrease of stretching frequency, while population analysis gave information on the mechanism of activation. It has been found that the presence of NO co-adsorbed on the same Cu + site as organic molecule resulted in more effective activation of C@O bond in acetone and formaldehyde, but resulted in a less effective activation of C@C and C„C bond in ethane and acetylene. On the other hand, the presence of organic molecule resulted in more effective activation of N@O bond (more important bond weakening) in NO molecule. The most significant N@O bond weakening took place if NO was co-adsorbed with acetone or formaldehyde. Both acetone and form- aldehyde transmit the most negative charge to the Cu + -zeolite system if adsorbed ‘‘solo’’ in Cu-zeolite. This negative charge may be next transmitted to antibonding NO orbitals resulting in so important N@O bond weakening. Ó 2006 Elsevier B.V. All rights reserved. Keywords: DFT calculations; CuZSM-5; Co-adsorption; NO activation 1. Introduction Cu containing zeolites are active catalysts both in NO decomposition (e.g., [1–6]) and reduction [7] as well as in numerous reactions of organic molecules (e.g., [8–17]). Many of these reactions are reactions of molecules contain- ing p electrons. IR studies and DFT quantum chemical cal- culations evidenced that both NO and organic molecules containing p electrons (alkenes, acetylene, benzene acetone and formaldehyde) have been activated by p back donation of d electrons of Cu + to antibonding p * orbitals of mole- cules. DFT calculations evidenced also [18–21] that zeolite framework neutralized partially the positive charge of Cu + (to +0.3) and increased the HOMO energy, therefore Cu + ion became an electron donor. The activation of double bond in alkenes and of triple bond in acetylene resulted in a red shift of C@C and C„C bands of 78–115 cm À1 , and by 160 cm À1 , respectively [22,23]. Smaller frequency shift (Dm C@O = 39–57 cm À1 ) was observed for carbonyl group in acetone and formaldehyde [24], but the smallest effect was for benzene (Dm CAC = 13 cm À1 ) [25], the LUMO orbital of which had only a little antibonding character. Besides of p back donation (donation of electrons toward molecule), p donation (donation from p bonding orbitals toward ion) also takes place. The electrical net charge on molecule depends on the balance between p back donation and p donation. According to the results of DFT calculations alkene and benzene molecules got negative charge when interacting with Cu + in zeolite, indicating that p back donation prevailed over p donation Acetylene remained neutral indicating that p back donation and p donation equilibrated. Both acetone and formaldehyde got positive charge indicating, that the donation of elec- trons from molecules to Cu + prevailed over p back dona- tion. In the cases of acetone and formaldehyde the 0166-1280/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2006.06.031 * Corresponding author. Tel.: +48126336377; fax: +48126340515. E-mail address: kozyra@chemia.uj.edu.pl (P. Kozyra). www.elsevier.com/locate/theochem Journal of Molecular Structure: THEOCHEM 778 (2006) 35–40