Cu-I-Y and Cu-II-Y zeolites: A XANES, EXAFS and visible-NIR study

We report a XANES, EXAFS and visible-NIR study on the local copper environment in Cu-I-Y prepared by an original gas-phase reaction of H-Y with CuCl and in Cu-II-Y prepared by conventional ion exchange with an aqueous cupric salt. XANES and visible-NIR techniques prove that the copper species in the so-prepared samples have the desired oxidation state. EXAFS reveals the presence of Cu-Cu bonds in Cu-II-Y thus indicating the presence of Cu dimers, As far as Cu-I-Y is concerned, only Cu-O first shell bonds were observed. This is remarkable since it proves that even in a nearly totally exchanged zeolite with Si/Al = 3 our preparation method allows the creation of only isolated Cu-I species. An oxygen coordination number ranging from 2.8 to 3.0 suggests that copper cations are mainly located in sites I', II and II', The reduction of Cu-I-Y with CO, leads to the formation of small copper metal clusters well identified by EXAFS and visible-NIR spectroscopies.