STUDY OF THE SURFACE SPECIES FORMED FROM THE INTERACTION OF NO AND CO WITH COPPER IONS IN ZSM-5 AND Y-ZEOLITES

The interaction of NO with copper in Cu-ZSM-5 and Cu-Y catalysts has been studied by IR techniques and TPSR. The adsorption of CO was followed by DRIFTS. Adsorption of CO on Cu-ZSM-5 and Cu-Y at room temperature gives bands corresponding to chemisorption on Cu+ in both cases, with those formed on Cu-ZSM-5 being the more stable in the temperature range up to 473 K. Upon adsorption of NO on Cu-ZSM-5 at room temperature bands corresponding to chemisorption on both Cu+, including those for the dinitrosyl species, and Cu2+ appear. On Cu-Y only bands belonging to species bound to Cu2+ are detected. This suggests that the Cu+ sites in Cu-Y are rapidly oxidized to Cu2+ by contact with NO, whereas Cu-ZSM-5 stabilizes Cu+ ions. Above 373 K, no NO species were detected on the Cu-Y sample, however with Cu-ZSM-5, bands for the mononitrosyls on both Cu+ and Cu2+ appear at higher temperatures (< 473 K). On the other hand, TPSR experiments corroborate that NO interacts stronger with copper in Cu-ZSM-5 than with that in Cu-Y. The implications of these findings on the mechanism of the NO decomposition are indicated.