Preparation effects on the activity of Cu-ZSM-5 catalysts for NO decomposition

Effects of Cu-ZSM-5 catalyst preparation on the activity of over-exchanged copper for NO decomposition are reported. The Cu-ZSM-5 catalysts were prepared by incorporating Cu²⁺ cations into ZSM-5 zeolites from an aqueous cupric acetate solution adjusted to different pH values by adding either acetic anhydride or aqueous ammonia in the solution. The Cu²⁺ exchange levels increased with increasing pH level. STEM/EDX analysis identified CuO particles (5–6 nm) on the zeolite surface for the materials exchanged at pH>6. Conversion and kinetics measurements of NO decomposition to N₂ over these catalysts showed that the over-exchanged copper was not active. Short-time wash with aqueous ammonia removed this copper. The catalyst activity correlated very well with the amount of copper remaining in the ZSM-5 channels.