REDOX CHEMISTRY IN EXCESSIVELY ION-EXCHANGED CU/NA-ZSM-5

TPR/TPD and FTIR arc used to characterize "excessively ion-exchanged" Cu/Na-ZSM-5. After calcination in O2 at 773 K at least two copper-oxygen species are present in addition to Cu2+ ions; these have been identified as CuO and [CU-O-Cu]2-. Reduction in H-2 transforms all these into Cu0 below 773 K. [Cu-O-Cu]2+ is autoreduced to Cu+ during outgassing. Reoxidation of Cu0 by zeolite protons to Cu+ is observed above 723 K in He or Ar; in the presence of CO this process is considerably enhanced and observed at much lower temperature, because CO is strongly adsorbed on Cu+. At 293 K CO adsorption causes reversible changes in the FTIR spectra.