The site-specificity of the CO probe molecule interaction with the Cu+/MFI system is investigated by a combination of experimental and theoretical techniques. Three Cu+ site types differing in CO adsorption energies (E-ads) were identified. Based on a very good agreement of experimental and calculated E-ads, the detail information about the structure and localization of Cu+ sites in MFI, including information about the localization of framework Al atom can be obtained. The IR spectra of CO adsorbed on the same Cu+/MFI samples clearly shows that the CO stretching frequencies are not site-specific in Cu+/MFI system. This conclusion is supported by calculated CO frequencies that do not depend on the Cu+ site type. (c) 2004 Elsevier B.V. All rights reserved.