A comparison of hydrothermal aging effects on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts
A comparison of hydrothermal aging effects on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts
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DOI：
10.1016/j.apcatb.2014.10.020
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发表时间：
2015-04-01
影响因子：
22.1
通讯作者：
Epling, William S.
中科院分区：
文献类型：
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作者：
Wang, Di;Jangjou, Yasser;Epling, William S.
比较了水热老化对Cu-SSZ-13和Cu-SAPO-34选择性催化还原性能的影响。在750℃水热老化16 h时，两种材料的NO转化率都有所保持，但在800℃水热老化后，两种材料的NO转化率都出现了显著差异。Cu-SSZ-13样品在所有测试温度下的NO转化率都显著降低，而Cu-SAPO-34样品仍保持了较高的SCR活性。事实上，Cu-SAPO-34在低温（低于350℃）下的NO转化甚至在高温处理后得到了增强，这表明活性位点的增加，这可能是由于高温驱动的后固态离子交换过程。同样，对于Cu-SAPO-34样品，NH3-TPD结果表明，与新鲜样品相比，750℃和800℃热液老化后，Lewis酸位点增加。然而，对于Cu-SSZ-13样品，DRIFTs表征结果表明，在800℃老化时，酸位（Bronsted和Lewis）减少，交换Cu2+位的数量显著减少，导致SCR活性急剧下降。XRD结果还表明，800℃水热时效后Cu-SSZ-13的CHA （chabazite）结构发生了破坏，而相同时效条件下Cu-SAPO-34的CHA （chabazite）结构仍然存在。除SCR性能外，还对SCR催化剂的NH3氧化活性和对NOx的选择性等关键功能进行了评价。在Cu-SSZ-13上，750℃的初始时效导致NH3氧化和对NOx的选择性增加，表明分离的Cu2+位点聚集成CuO颗粒，而在800℃的进一步时效导致结构崩溃，导致NH3氧化活性下降，XRD证实了这一点。另一方面，对于Cu-SAPO-34，水热老化后NH3氧化无明显变化。所有SCR性能测试、NH3氧化和表征结果一致表明，在本文所研究的配方和条件下，Cu-SAPO-34比Cu-SSZ-13更能经受水热老化。(C) 2014 Elsevier B.V.版权所有
The impacts of hydrothermal aging on the selective catalytic reduction (SCR) performance of both Cu-SSZ-13 and Cu-SAPO-34 were compared. Upon 750 degrees C hydrothermal aging for 16 h, the NO conversions on both materials were somewhat maintained, however, a significant difference appeared after hydrothermal aging at 800 degrees C. The Cu-SSZ-13 sample resulted in remarkably lower NO conversions at all temperatures tested while the Cu-SAPO-34 still maintained its high SCR activity. In fact, the NO conversions at low temperatures (below 350 degrees C) over Cu-SAPO-34 were even enhanced upon high temperature treatment, suggesting an increase in active sites, which is possibly due to a post solid state ion exchange process driven by high temperatures. Consistently, for the Cu-SAPO-34 sample, NH3-TPD results suggest an increase in Lewis acid sites after hydrothermal aging at 750 and 800 degrees C as compared with the fresh one. However, for the Cu-SSZ-13 sample, DRIFTs characterization results suggest a decrease in acid sites (Bronsted and Lewis), and a significant reduction in the amount of exchanged Cu2+ sites upon aging at 800 degrees C, leading to a drastically decreased SCR activity. XRD results also showed the CHA (chabazite) structure collapses for Cu-SSZ-13 after 800 C hydrothermal aging of Cu-SSZ-13, but still remains for Cu-SAPO-34 upon the same aging. Besides SCR performance, critical functions of the SCR catalyst including NH3 oxidation activity and selectivity to NOx, were also evaluated. Over Cu-SSZ-13, initial aging at 750 degrees C results in increased NH3 oxidation and selectivity to NOx, suggesting the aggregation of isolated Cu2+ sites into CuO particles, while further aging at 800 degrees C leads to decreased NH3 oxidation activity due to structure collapse as evidenced by XRD. On the other hand, for Cu-SAPO-34, no significant change in NH3 oxidation was observed after hydrothermal aging. All SCR performance test, NH3 oxidation and characterization results consistently indicate that Cu-SAPO-34 is more robust than Cu-SSZ-13 towards hydrothermal aging for the formulations and conditions examined here. (C) 2014 Elsevier B.V. All rights reserved.