Propene surface species and their role in NO reduction over Cu-ZSM-5 in the excess of oxygen

The nature and reactivity of surface complexes under the conditions of NO r eduction by propene over Cu-ZSM-5 in the excess of oxygen are studied in si tu by IR spectroscopy. The pi- and pi-allyl complexes are formed during the interaction of C3H6 or C3H6 + O-2 With the zeolite surface at low temperat ures, whereas coke is formed at higher temperatures. Complexes with organic nitro compounds are observed in the presence of NO at relatively low tempe ratures, and nitrito complexes are found under the reaction conditions (300 degrees C). NO reduction by propene over Cu-ZSM-5 in the excess of O-2 occ urs via two routes. One involves the formation of coke on the surface follo wed by the interaction of coke with NO to yield the reaction products. In t his process, coke by itself serves is a reducing agent. In this reaction, c opper ions increase the rate of the coke formation and change the ratio bet ween the amounts of "soft" and "hard" coke. The other route involves the re action between propene and the Cu2+-O-N=O complex formed on copper ions fol lowed by the formation of reaction products. This process is analogous to t hat observed earlier for NOx, reduction by propane in these systems.