The　hydrothermal　stability　of　the　CuSSZ-13　samples　with　various　Si/Al　ratios　was　examined.　The　NO　conversions　in　the　NH3-SCR　and　NH3　oxidation　were　measured.　Physicochemical　properties　of　the　samples　were　characterized　by　means　of　a　number　of　analytical　techniques.　It　is　shown　that　the　NH3-SCR　activity　and　hydrothermal　stability　of　the　CuSSZ-13　samples　decreased　with　the　rise　in　Si/Al　ratio.　Such　decreases　were　attributed　to　the　drop　in　the　amount　of　the　isolated　Cu2+　in　the　D6R　and　CHA　cage　of　the　CuSSZ-13　samples.　Part　of　the　isolated　Cu2+　ions　were　transformed　to　CuO　after　hydrothermal　aging　treatment,　especially　in　the　high-Si/Al-ratio　samples.　A　large　amount　of　the　aggregated　CuO　destroyed　the　skeleton　structure　of　SSZ-13,　leading　to　the　deactivation　of　the　samples.　(C)　2017　Elsevier　B.V.　All　rights　reserved.