Migration of cations and shell functionalization for Cu-Ce-La/SSZ-13@ZSM-5: The contribution to activity and hydrothermal stability in the selective catalytic reduction reaction

Abstract

A core–shell structure Cu–Ce–La/SSZ-13@ZSM-5 catalyst with a Cu–Ce–La/SSZ-13 core and a ZSM-5 shell was first synthesized by a self-assembly method and used for ammonia-selective catalytic reduction (NH3-SCR). In comparison with Cu–Ce–La/SSZ-13, Cu–Ce–La/SSZ-13@ZSM-5 with appropriate shell thickness presents better SCR activity and hydrothermal stability. We discovered an ion migration effect during the shell phase assembly process and further proposed that the ion migration effect was induced by the dissolution of the core phase during the growth of the shell. Part of the metal ions were migrated and redistributed during the assembly of the ZSM-5 shell, resulting in the transformation of [Cu(OH)]+–Z to Cu2+–2Z species and the functionalization of the shell phase. The functionalized shell is beneficial for the adsorption and activation of NH3. The results of an H2O resistance test and thermogravimetric analysis confirm that the coating of the hydrophobic shell can effectively improve the hydrothermal stability and H2O resistance of core–shell Cu–Ce–La/SSZ-13@ZSM-5.