Influence of silver on the catalytic activity of Cu-ZSM-5 for NO SCR by propane. Effect of the presence of water and hydrothermal agings

The effect of silver on the activity and hydrothermal stability of Cu-ZSM-5 for NOx reduction with C3H8 under oxidizing and wet conditions has been in vestigated. The addition of silver as a cocation to Cu-ZSM-5 catalysts decr eases the reversible inhibition by water occurring under catalytic conditio ns when the temperature does not exceed 773 K. Furthermore, it suppresses t he irreversible deactivation observed when the reaction is performed up to 873 K. In effect, the Cu-Ag-ZSM-5 solids are more resistant to the dealumin ation induced by the acids formed by reactions between NO, O-2 and H2O than the Cu-ZSM-5 ones. The presence of silver provides also an higher hydrothe rmal stability under an (air + 10 vol% H2O) mixture if the temperature does not exceed 973 K. The catalytic activity and the deactivation behaviour ar e dependent on the concentration of silver and copper and more especially o n the preparation procedure.