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Nature of Cu Active Centers in Cu-SSZ-13 and Their Responses to SO2 Exposure
ACS Catalysis ( IF 12.9 ) Pub Date : 2018-01-19 00:00:00 , DOI: 10.1021/acscatal.7b03095
Yasser Jangjou 1 , Quan Do 2 , Yuntao Gu 1 , Laura-Gaile Lim 2 , Hong Sun 2 , Di Wang 3 , Ashok Kumar 3 , Junhui Li 3 , Lars C. Grabow 2 , William S. Epling 1
Affiliation  

The effect(s) of SO2 on the two types of active sites on Cu-SSZ-13 NH3–SCR catalysts, Z2Cu and ZCuOH, were investigated. Two Cu-SSZ-13 catalysts with Si:Al ratios of 6 and 30 were synthesized, and they provide very different distributions of these two active sites. Inductively coupled plasma optical emission spectroscopy (ICP-OES), H2 temperature-programmed reduction (H2-TPR), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were utilized to characterize catalyst samples and quantify the amounts of total Cu, Z2Cu and ZCuOH. In situ DRIFTS results show that Z2Cu and ZCuOH responses to low-temperature (<200 °C) SO2 poisoning were site-dependent. Results of SO2 and SO2 + NH3 temperature-programmed desorption (TPD) and DRIFTS experiments, supplemented with DFT calculations, revealed that the different observed responses correspond to different sulfur intermediates that form. On Z2Cu sites, SO2 only adsorbs when it is cofed with NH3 via formation of ammonium sulfate, with its fingerprint TPD feature at 380 °C. However, low-temperature interaction between SO2 and ZCuOH leads to copper bisulfite species formation, which can be further oxidized to form copper bisulfate with increasing temperature. In terms of low-temperature SCR functionality, the activity of both Cu-SSZ-13 samples were found to be significantly inhibited by SO2. However, in terms of regeneration (i.e., desulfation) behavior, Cu-SSZ-13 with a Si:Al = 30 (higher ZCuOH compared to Z2Cu) seemed to require higher desulfation temperatures (>550 °C). Therefore, compared with Z2Cu, ZCuOH sites are more susceptible to severe low-temperature SO2 poisoning because of the formation of more stable bisulfite and ultimately bisulfate species.

中文翻译:

Cu-SSZ-13中Cu活性中心的性质及其对SO 2暴露的响应

研究了SO 2对Cu-SSZ-13 NH 3 -SCR催化剂Z2Cu和ZCuOH两种类型的活性中心的影响。合成了两种Si:Al比为6和30的Cu-SSZ-13催化剂,它们提供了这两个活性位点非常不同的分布。利用电感耦合等离子体发射光谱(ICP-OES),H 2程序升温还原(H 2 -TPR)和漫反射红外傅里叶变换光谱(DRIFTS)表征催化剂样品并量化总Cu,Z2Cu的量和ZCuOH。原位DRIFTS结果表明,Z2Cu和ZCuOH对低温(<200°C)SO 2中毒的响应与位置有关。SO 2的结果SO 2 + NH 3程序升温脱附(TPD)和DRIFTS实验,加上DFT计算,表明观察到的不同响应对应于形成的不同硫中间体。在Z2Cu部位,仅当SO 2通过形成硫酸铵与NH 3结合时才吸附,SO 2在380°C时具有指纹TPD特性。然而,SO 2和ZCuOH之间的低温相互作用导致亚硫酸氢铜物质的形成,随着温度的升高,亚硫酸氢铜可以进一步氧化形成亚硫酸氢铜。就低温SCR功能而言,发现两个Cu-SSZ-13样品的活性均受到SO 2的显着抑制。。然而,就再生(即脱硫)行为而言,具有Si:Al = 30(比Z2Cu更高的ZCuOH)的Cu-SSZ-13似乎需要更高的脱硫温度(> 550°C)。因此,与Z2Cu相比,由于形成了更稳定的亚硫酸氢盐并最终形成了硫酸氢盐,ZCuOH位点更容易受到严重的低温SO 2中毒的影响。
更新日期:2018-01-19
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