Improvement of low-temperature hydrothermal stability of Cu/SAPO-34 catalysts by Cu2+ species

• Hydrothermal treatment at 70 °C caused the collapse of Cu/SAPO-34 structure.
• The collapse mechanism was the breakage of Si–O–Al bonds.
• Hydrothermal stability of Cu/SAPO-34 enhanced by introducing Cu2+ species.
• Hydrothermal treatment also caused the decrease of SCR activity.
• Isolated Cu2+ was both SCR active site and structure protective agent.

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 °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 Brønsted 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.

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