The effect of synthesis methods on Cu species and active sites over Cu/SAPO-34 for NH3-SCR reaction

Abstract

The changed status of copper species and active Cu sites of NH₃-SCR over the Cu/SAPO-34 zeolites synthesized by three different methods has been investigated in this work. The combination of the EPR, H₂-TPR and SEM results demonstrate that different synthesis methods do not affect the types of Cu species, but affect the distribution. The dominant Cu species is CuO-clusters for the precipitation sample, and it is isolated Cu²⁺ for the ion-exchange sample. While, for the one-pot catalyst, both isolated Cu²⁺ and surface CuO species are present in comparable amount. Additionally, hydrothermal treatment can also change the distribution of Cu species, it prompts the migration of Cu species from the external surface CuO into the ion exchange locations and forms more isolated Cu²⁺. The kinetic results show all the Cu/SAPO-34 catalysts display the same apparent activation energy and TOF values, indicating that the three synthetic methods do not change the reaction pathway of NH₃-SCR and the active Cu sites (isolated Cu²⁺ in the vicinity of six-membered rings).