The destructive effect of H2O on SAPO-34 framework and Cu2+ species protection mechanism at low temperature were studied in this research. A series of Cu/SAPO-34 samples with varying Cu loadings (0-6.78 wt%) were hydrothermally treated at 70 degrees C with 80% humidity. Textural characterization results showed that this treatment led to the collapse of SAPO-34 framework at zero or low Cu loadings, which was caused by the breakage of Si-O-Al bonds proved by ex-situ DRIFTS and NMR results. The copper content increase enhanced SAPO-34 stabilization. Selective catalytic reduction (SCR) reaction rates were severely reduced after the treatment, while this decrease was gradually suppressed with increasing Cu loading up to 6.78 wt%. NH3-TPD and EPR results revealed that both the number of Bronsted acid sites and Cu2+ species decreased after the treatment, which likely contributed to the reduced SCR reaction rates. Our study indicated that the isolated Cu2+ ions were both SCR active site and structure protective agent. (C) 2014 Elsevier Inc. All rights reserved.