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 env ironment in Cu-I-Y prepared by an original gas-phase reaction of H-Y w ith CuCl and in Cu-II-Y prepared by conventional ion exchange with an aqueous cupric salt. XANES and visible-NIR techniques prove that the c opper species in the so-prepared samples have the desired oxidation st ate. EXAFS reveals the presence of Cu-Cu bonds in Cu-II-Y thus indicat ing 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 pre paration method allows the creation of only isolated Cu-I species. An oxygen coordination number ranging from 2.8 to 3.0 suggests that coppe r 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.