The design of photocatalysts for the removal of NOx at normal temperatures—Copper (I) and silver (I) ion catalysts anchored within zeolite cavities

The Cu⁺/ZSM-5 and Ag⁺/ZSM-5 catalysts were prepared by a combination of ion-exchange and thermovacuum treatments. In situ photoluminescence, ESR, XAFS, UV-VIS and FT-IR measurements of the catalysts revealed that within the cavity of the ZSM-5 zeolite, the Cu⁺ ion or Ag⁺ ion exists in an isolated state. UV irradiation of the catalysts in the presence of NO at normal temperature led to the formation of N₂ and O₂ for Cu⁺/ZSM-5 and N₂, N₂O and NO₂ for Ag⁺/ZSM-5, indicating that the isolated Cu⁺ ion or Ag⁺ ion acts as a photocatalyst for the direct decomposition of NO. However, the Cu⁺/ZSM-5 catalyst loses its photocatalytic reactivity under the coexistence of O₂, while the Ag⁺/ZSM-5 catalyst maintains its reactivity under the coexistence of O₂ and H₂O.