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 CuI-Y prepared by an original gas-phase reaction of H-Y with CuCl and in CuII-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 CuII-Y thus indicating the presence of Cu dimers. As far as CuI-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 CuI 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 CuI-Y with CO, leads to the formation of small copper metal clusters well identified by EXAFS and visible-NIR spectroscopies.