Abstract:

Using wet impregnation method to mimic alkali metal poison of ammonia-selective catalytic reduction (NH₃-SCR) catalysts, Cu-based micropore zeolites Cu/SSZ-13 and Cu/SAPO-34 with different Na contents(mass fraction) were prepared, and the Na poisoning mechanism on them was studied. The results show that the externally introduced Na ions can severely affect the NH₃-SCR catalytic activity of the two catalysts, resulting in the collapse of the crystal structure of the catalyst, the decrease of acidity and the reduction of active species. In detail, when Na content was less than 1.82%, Cu/SAPO-34 has higher resistance of Na ions than Cu/SZZ-13; while when Na> 3.48%, Cu/SAPO-34 catalysts almost deactivated thoroughly. By structural characterization (BET, XRD and SEM) and acidity characterization (DRIFTS, NH₃-TPD and H₂-TPR), it was found that with Na poisoning deeper and deeper, Cu/SSZ-13 took a gradual style of the structural destruction, but Cu/SAPO-34 adopted a sudden way. Studies on the mechanism of Na poisoning show that the decrease of acid sites is the main reason for the decrease of SCR activity of Cu/SSZ-13, and the structural collapse is the main reason for the decrease of SCR activity of Cu/SAPO-34.

Key words: selective catalytic reduction, alkali metal, zeolite, catalysts, nitric oxide, poison mechanism

摘要：

以浸渍法模拟碱金属中毒NH₃-SCR催化剂过程，制备不同Na含量（质量分数）的铜基小孔分子筛Cu/SSZ-13和Cu/SAPO-34，对比研究了二者的碱金属中毒机理。结果表明，外引Na离子均可严重影响两种催化剂的NH₃-SCR催化活性，造成催化剂的晶相结构坍塌，酸性量减少，活性物种减少。不同的是，Na引入量较低（<1.82%）时，Cu/SAPO-34比Cu/SSZ-13具有更强的Na离子耐受性，而当Na含量高于3.48%时，Cu/SAPO-34几乎完全丧失NH₃-SCR催化活性。通过催化剂的结构表征（BET、XRD和SEM）和酸性位表征（DRIFTS、NH₃-TPD和H₂-TPR），研究表明随着Na中毒程度的加深，Cu/SSZ-13的结构破坏是渐变式的，而Cu/SAPO-34的结构破坏是突变式的；Na中毒的机理研究表明，酸性位的减少是Cu/SSZ-13的SCR活性下降的主导原因，结构坍塌是Cu/SAPO-34的SCR活性下降的主导原因。

关键词: 选择性催化还原, 碱金属, 分子筛, 催化剂, 氮氧化物, 中毒机理