Thermostable Molecular Sieves, Silicoaluminophosphate (SAPO)-34, for the Removal of NO_X with C₃H₆ in the Coexistence of O₂, H₂O, and SO₂

Selective reduction of NO with C₃H₆ under an oxidizing atmosphere was studied over various Cu ion-exchanged molecular sieves. All examined Cu ion-exchanged catalysts are active for NO reduction with C₃H₆ in a large excess of O₂; however, the temperature at the maximum NO conversion depends on the kind of molecular sieves. In particular, it was found that Cu-SAPO-34 is sometimes more active than Cu-ZSM-5. Thermal stability of SAPO-34 was extremely high, and consequently, decrease in the activity to NO selective reduction on Cu-SAPO-34 was negligible over 60 h at 673 K in an atmosphere containing 15 vol % H₂O. After thermal treatment at 1073 K in a humidified atmosphere, decrease in the activity to NO reduction was also small. Although the activity of Cu-SAPO-34 to NO reduction was decreased slightly with the coexistence of SO₂, it is expected that the activity of Cu-SAPO-34 is sustained over a long period.