Understanding Na functions on distribution of Cu species within Cu-SSZ-13 for the selective reduction of NOx with NH3

Abstract

Cu-SSZ-13 catalysts have been extensively investigated for NH3-SCR over numerous years. However, whether sodium (Na) promoted or inhibited the NH3-SCR performance of Cu-SSZ-13 catalysts was still controversial and needed to be further elucidated. In this work, two Cu-SSZ-13 catalysts, one containing Na and the other without Na, were prepared through a stepwise ion-exchange technique. The objective was to explore the promoting influence of Na on both catalytic activity and hydrothermal stability of Cu-SSZ-13. Analysis via H2-TPR and NH3-DRIFTS revealed a notable increase in the formation of [Cu(OH)]+-Z species due to the presence of Na. DFT calculations stimulated the ion-exchange process, and confirmed the migration of Cu species from 6MR to 8MR sites in the presence of Na. This study provides direct experimental evidence regarding the influence of Na on Cu distribution, thereby deepening the understanding of the interaction between Cu sites and co-cations.