Department of Chemistry, INSTM Reference Center and NIS Center, University of Turin, Address Via Giuria 7, I-10135, Turin, Italy.
Umicore Denmark ApS, Nøjsomhedsvej 20, 2800, Kgs. Lyngby, Denmark.
Chemistry. 2018 Aug 14;24(46):12044-12053. doi: 10.1002/chem.201802769. Epub 2018 Jul 26.
In this work, we show the potentiality of operando FTIR spectroscopy to follow the formation of Cu -(N,O) species on Cu exchanged chabazite zeolites (Cu-CHA), active for the selective catalytic reduction of NO with NH (NH -SCR). In particular, we investigated the reaction of NO and O at low temperature (200 and 50 °C) on a series of Cu-CHA zeolites with different composition (Si/Al and Cu/Al ratios), to investigate the nature of the formed copper nitrates, which have been proposed to be key intermediates in the oxidation part of the SCR cycle. Our results show that chelating bidentate nitrates are the main structures formed at 200 °C. At lower temperature a mixture of chelating and monodentate nitrates are formed, together with the nitrosonium ion NO , whose amount was found to be proportional to the zeolite Brønsted site concentration. Nitrates were found to mainly form with Cu ions stabilized by one negative framework charge (Z), Z-[Cu(OH] or Z-[Cu(O ] , without involvement of Z -Cu ones. This evidence, together with the absence of bridging nitrates in samples with high probability for Cu-Cu pairs, indicate that the nitrate ligands are not able to mobilize copper ions, at variance with what recently reported for NH . Finally, water was found to replace preformed chelating copper nitrates and deplete NO (though with different kinetics) at both temperatures, while favouring the presence of monodentate ones.
在这项工作中，我们展示了原位傅里叶变换红外光谱法在跟踪铜交换丝光沸石（Cu-CHA）上 Cu-（N，O）物种形成方面的潜力，Cu-CHA 是用于选择性催化还原 NO 与 NH 的活性物质（NH-SCR）。特别是，我们研究了在一系列组成不同（Si/Al 和 Cu/Al 比）的 Cu-CHA 沸石上，NO 和 O 在低温（200 和 50°C）下的反应，以研究所形成的硝酸铜的性质，它们被认为是 SCR 循环氧化部分的关键中间体。我们的结果表明，在 200°C 时形成的主要结构是螯合双齿硝酸盐。在较低温度下，形成了螯合和单齿硝酸盐的混合物，以及硝酰正离子 NO+，其数量与沸石的 Brønsted 位浓度成正比。发现硝酸盐主要与由一个负骨架电荷（Z）稳定的 Cu 离子形成，Z-[Cu（OH）]或 Z-[Cu（O）]，而不涉及 Z-Cu 型。这一证据，再加上在高概率存在 Cu-Cu 对的样品中不存在桥接硝酸盐，表明硝酸盐配体不能使铜离子移动，这与最近关于 NH 的报道不同。最后，在两种温度下，水被发现都能取代预形成的螯合铜硝酸盐并耗尽 NO（尽管动力学不同），同时有利于单齿硝酸盐的存在。
