The deactivation mechanism of Cu/SAPO-34 ammonia selective catalytic reduction catalysts (NH 3 -SCR) by SO 2 poisoning has been systematically investigated using a range of analytical techniques in order to study the influence on both the zeolitic framework and the active Cu 2+ ions. The different sulfate samples were obtain by SO 2 poisoning over Cu/SAPO-34 NH 3 -SCR catalysts as functions of the time and concentration in the feed. The obtained results reveal that the SO 2 poisoning could seriously decrease the NO conversion during the whole temperature range (100 o C-500 o C). support. The ex-situ DRIFTS and BET results expose that the SO 2 poisoning does a less pronounced affect on its framework structure. The TPR and EPR results domonstrate that SO 2 poisoning does a significant influence on the coordination environment and the content of the active isolated Cu 2+ species. The kinetic results demonstrate the SO 2 poisoning does not influence the apparent activation energy (Ea) of NH 3 -SCR reaction over Cu/SAPO-34 catalysts. The decline of the NH 3 -SCR activity is due to the reduction of the number of isolated Cu 2+ ions.World-wide news on poor air quality in Chinese cities was quite common since 2013. Some of the leading contributors are the pollutants emitted from increasing automotives. These environmental problems have resulted in a continuous decrease of the allowed NOx concentrations due to stringent emission regulations. Ammonia selective catalytic reduction (NH 3 -SCR) was considered as the technology with the highest potential to meet strict future diesel emissions standards in mobile applications.Well established NH 3 -SCR technique uses either V 2 O 5 /WO 3 -TiO 2 or Zeolite based catalysts. Zeolite-based catalysts promoted by transition metal such as Fe and Cu represent an excellent solution to overcome the stability problems of V 2 O 5 -based catalysts but may show disadvantages in stability after hydrothermal ageing and sulphur poisoning [1][2][3] . Recently, Bull and Kwak et al [4][5][6][7] reported the small-pore zeolite (~3.8 A) with the CHA structure show significant promise as the new leading candidate among zeolite formulations compared to the Cu/ZSM-5 and Cu/Beta. Bull and Andersen et al [8,9] firstly reported the NH 3 -SCR activity of Cu/SAPO-34 catalyst.In addition, Fickel and others found that Cu/SAPO-34 catalysts perform superior NH 3 -SCR activity and prominent hydrothermal stability at 750 o C to that of Cu/zeolites was related to their unique microporous structure [5,7] . Meanwhile,
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