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The preliminary mechanism research of NH3-SCR and NH3 oxidation over Cu/SAPO-34 catalyst is explored. The XRD, SEM, in situ EPR, NH3-SCR, NH3 oxidation test, DRIFTs, and the kinetic tests were performed for the bulk characterization, catalytic activity measurement, and the mechanism estimation. The NH3-SCR result showed that Cu/SAPO-34 revealed excellent activity during 120–600 °C, while the NH3 oxidation appeared above 300 °C and caused the decline of NO conversion. The order of various reactants (NO, NH3, and O2 for NH3-SCR and NH3, O2, for NH3 oxidation) was estimated by the kinetic tests to explain their behaviors during the NH3-SCR process. The NH3-SCR presents strong dependence on adsorbed NH3 species on Cu/SAPO-34, but the NH3 oxidation does not. Furthermore, the EPR experiment proved that the isolated Cu2+ species are the active sites and the ammonia nitrites species are the intermediate for NH3-SCR over Cu/SAPO-34 catalysts. The different behavior of adsorbed NH3 species in NH3-SCR and NH3 oxidation was studied through DRIFTs to explain the competition between the two reactions for NH3 consumption at high temperature. Meanwhile, combining the results of previous research, the primary reaction mechanism over Cu/SAPO-34 during the NH3-SCR process was conducted.

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The changed status of copper species and active Cu sites of NH 3 -SCR over the Cu/SAPO-34 zeolites synthesized by three different methods has been investigated in this work. The combination of the EPR, H 2 -TPR and SEM results demonstrate that different synthesis methods do not affect the types of Cu species, but affect the distribution. The dominant Cu species is CuO-clusters for the precipitation sample, and it is isolated Cu 2+ for the ion-exchange sample. While, for the one-pot catalyst, both isolated Cu 2+ and surface CuO species are present in comparable amount. Additionally, hydrothermal treatment can also change the distribution of Cu species, it prompts the migration of Cu species from the external surface CuO into the ion exchange locations and forms more isolated Cu 2+ . The kinetic results show all the Cu/SAPO-34 catalysts display the same apparent activation energy and TOF values, indicating that the three synthetic methods do not change the reaction pathway of NH 3 -SCR and the active Cu sites (isolated Cu 2+ in the vicinity of six-membered rings).

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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,

In this study, the mechanism of ammonium bisulfate (ABS) formation and decomposition over V/WTi for the NH-selective catalytic reduction (SCR) at various temperatures was deeply investigated. Bridged bidentate, chelating bidentate, and tridentate sulfates bound to TiO were formed as dominant intermediates at 200, 250, and 300 °C, respectively. These sulfates reacted with affinitive ammonium species to form ammonium (bi)sulfate species and also covered the active sites and embedded the VOSO intermediates, which resulted in an inferior intrinsic NH-SCR conversion rate at 200 °C and 250 °C. At 300 °C, trace amounts of ABS on TiO presented no influence on the NH-SCR performance. The electrons deviating towards sulfates through the bond between ABS and metal oxides (WO and TiO) weakened the stability of ABS and lowered its decomposition temperature, whereas the vanadia species played the opposite role due to the sulfur species existing in an electron saturation state with the formation of the VOSO intermediate. The presence of NO + O could break the bonds inside ABS and it could react with the ammonium species originating from ABS, which pulls NH out of the ABS formation equilibrium and accelerates its decomposition and competitively inhibits its formation. Correspondingly, the faster NH-SCR conversion rate and higher N selectivity improve the ABS poisoning resistance of the V/WTi catalyst at low temperatures.