Cu-MCM-22 zeolite: A combined X-ray powder diffraction and computational study of the local structure of extra-framework copper ions

Local structure and site distribution of extra-framework copper ions in Cu-exchanged MCM-22 zeolite have been determined by synchrotron radiation X-ray powder diffraction analysis combined with ab-initio molecular orbital (DFT) calculations. Three Cu sites (S_I, Su_II and S _III) in 6-membered rings and one site (S_VI) in a 5-membered ring close to the inter lamellar region, were located inside the MCM-22 supercage, whereas no Cu ions were found within the sinusoidal channels. The existence of two families of Cu sites (in 5- and 6-membered rings respectively) with different steric hindrance and adsorptive capacity, as indicated by previous FTIR study of adsorbed NO [A. Frache, et al., Langmuir, 18 (2002) 6875], was fully confirmed in this study.