COPPER ION-EXCHANGED SAPO-34 AS A THERMOSTABLE CATALYST FOR SELECTIVEREDUCTION OF NO WITH C3H6

Selective reduction of NO with C3H6 in the presence of oxygen was stud ied over Cu ion-exchanged SAPO-n (n = 5, 11, 34), and Cu ion-exchanged Zeolites beta, USY, and ZSM-5. All the Cu ion-exchanged catalysts exh ibited high activity for NO reduction with C3H6 in a large excess of O -2; however, the temperature for maximum NO conversion depended on the kind of molecular sieve. Although the maximum conversion of NO was at tained at a slightly higher temperature in comparison with Cu-ZSM-5, C u-SAPO-34 exhibited the highest activity for NO reduction among the ca talysts studied under the conditions examined. Furthermore, high NO co nversion was attained over a wide temperature range, from 623 to 873 K . SAPO-34 has high thermal stability. High activity for NO selective r eduction on Cu-SAPO-34 was sustained for more than 60 h at 673 K in an atmosphere containing 15 vol% H2O. After thermal treatment at 1073 K in humidified atmosphere, the decrease in activity for NO reduction wa s also small. Redox behavior of Cu ions in SAPO-34 between monovalent and divalent states occurs during the selective reduction of NO, and t he reaction seems to proceed via formation of adsorbed nitrate species followed by the formation of organic nitro compounds. (C) 1997 Academ ic Press.