Facile Synthesis of Cu-Exchanged Zeolite Catalysts with Only Cu2+-2Z Species: Enhancing Hydrothermal Stability and Sulfur Resistance for NH3–SCR

Abstract

For Cu-exchanged zeolite catalysts, Cu²⁺ ions existing as Cu²⁺-2Z and [Cu(OH)]⁺-Z (where Z represents a framework negative charge) are considered the active sites for the selective catalytic reduction of NO_x with NH₃ (NH₃–SCR). Cu²⁺-2Z is more hydrothermally stable and sulfur poisoning-resistant than [Cu(OH)]⁺-Z. In this work, Cu-CHA and Cu-LTA catalysts containing only Cu²⁺-2Z species were successfully synthesized by a novel impregnation (NIM) method, exhibiting remarkably enhanced hydrothermal stability and sulfur resistance compared with any reported Cu-exchanged zeolite catalysts. It was also found that the [Cu(OH)]⁺-Z sites can convert to Cu²⁺-2Z by treating at high temperature (850 °C) due to the self-reduction of Cu²⁺ to highly mobile Cu⁺. The use of the NIM method not only significantly simplifies the preparation of the catalysts but also can precisely control the Cu loading, which is very important for the control of Cu species. Many other zeolite catalysts can be prepared by this method.