In Situ Spectroscopic Studies on the Redox Cycle of NH3−SCR over Cu−CHA Zeolites,ChemCatChem

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In Situ Spectroscopic Studies on the Redox Cycle of NH3−SCR over Cu−CHA Zeolites
ChemCatChem ( IF 3.8 ) Pub Date : 2020-02-25 , DOI: 10.1002/cctc.202000024
Chong Liu ₁ , Hiroe Kubota ₁ , Takehiro Amada ₁ , Kenichi Kon ₁ , Takashi Toyao _{1,

2} , Zen Maeno ₁ , Kakuya Ueda ₃ , Junya Ohyama _{2,

4} , Atsushi Satsuma _{2,

3} , Takuya Tanigawa ₅ , Nao Tsunoji ₅ , Tsuneji Sano ₅ , Ken‐ichi Shimizu _{1,

2}

Affiliation

The selective catalytic reduction of NO with ammonia (NH₃−SCR) catalyzed by Cu−CHA zeolites is thoroughly investigated using in situ spectroscopic experiments combined with on‐line mass spectroscopy (MS) under steady‐state NH₃−SCR conditions and transient conditions for Cu(II)/Cu(I) redox cycles. Quantitative analysis of the in situ XANES spectra of Cu−CHA under steady‐state conditions of NH₃−SCR show that NH₃‐coordinated Cu(II) species is the dominant Cu species at low temperatures (100–150 °C). At higher temperatures, Cu(II) species and [Cu(NH₃)₂]⁺ complex coexist, possibly because the rate of the Cu(II)→Cu(I) reduction step is comparable to that of the Cu(I)→Cu(II) oxidation step. In situ XANES, IR/MS, and UV‐vis/MS experiments on the reduction half cycle demonstrate that the reduction of Cu(II) species occurs via the reaction of NH₃‐liganded Cu(II) with NO to yield N₂ and H₂O. For the oxidation half cycle, in situ XANES experiments of Cu(I) oxidation in 10 % O₂ at 200 °C indicate that an increased density in CHA zeolite exhibits a higher oxidation rate. In situ UV‐vis experiments of Cu(I) reoxidation using different mixtures of oxidant feed gas demonstrate the key role of O₂ in the oxidation cycle. It is suggested that the reoxidation of Cu(I) to Cu(II) species occurs with only O₂ as the oxidant, and a high Cu density in CHA zeolite promotes SCR activity by enhancing the oxidative activation of Cu(I) to Cu(II) during the catalytic cycle.

中文翻译：

Cu-CHA沸石上NH3-SCR氧化还原循环的原位光谱研究

在稳态NH ₃ -SCR条件和瞬态条件下，结合原位光谱实验和在线质谱（MS），对Cu-CHA沸石催化的氨选择性催化还原NO（NH ₃ -SCR）进行了研究。用于Cu（II）/ Cu（I）氧化还原循环。在稳态NH ₃ -SCR条件下，Cu-CHA的原位XANES光谱定量分析显示，在低温（100-150°C）下，NH ₃配位的Cu（II）物种是主要的Cu物种。在较高温度下，Cu（II）和[Cu（NH ₃）₂ ] ⁺络合物并存，可能是因为Cu（II）→Cu（I）还原步骤的速率与Cu（I）→Cu（II）氧化步骤的速率相当。还原半衰期的原位XANES，IR / MS和UV-vis / MS实验表明，Cu（II）物种的还原是通过NH ₃配位的Cu（II）与NO反应生成N ₂和ħ ₂ O.用于氧化半周期中，在原位在10％氧气的Cu的XANES实验（I）氧化₂在200℃下表明，CHA沸石的增加的密度表现出更高的氧化速率。使用氧化剂进料气的不同混合物对Cu（I）进行再氧化的原位UV-vis实验证明了O ₂的关键作用在氧化循环中。建议仅以O ₂为氧化剂发生Cu（I）到Cu（II）物种的再氧化，CHA沸石中的高Cu密度通过增强Cu（I）到Cu（I）的氧化活化而促进SCR活性。 II）在催化循环中。

更新日期：2020-02-25

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