NO DECOMPOSITION OVER BICOMPONENT CU-SM-ZSM-5 ZEOLITES

Bicomponent Cu-Sm-ZSM-5 zeolites with different Cu and Sm contents hav e been investigated, and compared with monocomponent Cu-ZSM-5 and Sm-Z SM-5. Sm-ZSM-5 is almost inactive in NO decomposition, producing only N2O. Zeolites containing around 0.20 wt% Sm and between 2.2 and 2.7 wt % Cu are substantially more active than the pure Cu-ZSM-5, the increas e in NO transformation per total Cu atoms reaching 100%. The catalysts were studied using XPS, O-2-TPD and FT-LR of adsorbed NO. In addition , the transient period between the first contact of the catalyst with NO and 3 h was monitored. The bicomponent Cu-Sm-ZSM-5 catalysts exhibi t a very strong O-2-TPD band around 370 degrees C compared to the mono component catalysts. FT-IR shows a strong increase of NO adsorption in the (NO)(2) form, and a corresponding decrease of the bands of isolat ed adsorbed NO. The presence of Sm does not significantly prevent the loss of Cu dispersion during a heat treatment in helium, nor the Cu++/ Cu+ ratio. Although it is impossible to conclude unequivocally, it see ms that samarium has two roles. It modifies the exchange of copper wit h the zeolite and, consequently, the dispersion and aggregation of cop per. (C) 1998 Elsevier Science B.V.