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.　©　2024　Elsevier　B.V.