SITING AND REDOX BEHAVIOR OF CU IONS IN CUH-ZSM-5 ZEOLITES - CU+ PHOTOLUMINESCENCE STUDY

Sitting and redox properties of Cu ions in CuH-ZSM-5 zeolites differin g in Cu content and Si/Al framework ratio were investigated employing the Cu+ luminescence spectra. It was shown that two main Cu sites exis t in the ZSM-5 structure; one, reflected in the blue (480 nm) band, in close proximity to the two framework Al atoms and the second, yieldin g the yellow-green (540 nm) band, adjacent to one Al framework atom. T he former sites are preferentially occupied at low Cu content. The red ucibility of these sites is controlled by the content of the framework Al; with a lower framework charge, the reducibility (in both hydrogen and CO atmospheres) increases. The hydrogen reduction of Cu2+ passes from Cu+ to Cu-0, while reduction in CO yields practically only Cu+. I n addition, the two Cu sites differ in reducibility. The Cu sites with the blue luminescence are reduced faster regardless of whether hydrog en is used; however, the degree of their reduction up to Cu-0 is sligh tly lower compared to the Cu sites characterized by the yellow-green l uminescence.