The oxidation of NO to NO₂ and the subsequent reduction by NH₃via a NO⁺ intermediate over a proton-type chabazite zeolite (H-CHA) were investigated by the combination of in situ infrared (IR) spectroscopy and density functional theory (DFT) calculations. The in situ IR spectral results indicate that the NO⁺ species formed under a flow of NO + O₂ at 27–250 °C are more stable at lower temperatures over both H-CHA and copper-cation-exchanged CHA zeolite (Cu-CHA). The Arrhenius plot (T = 27–120 °C) shows a negative apparent activation barrier energy (−11.5 kJ mol^–1) for the formation of NO⁺ species under the NO + O₂ flow over H-CHA. The time course of the IR spectra at 27 °C shows that NO is oxidized by O₂ to NO₂ and then further converted via N₂O₄ to NO⁺ and NO₃^–. The subsequent exposure to NH₃ at 27 °C reduces the NO⁺ species to N₂. DFT calculations revealed that Brønsted acid sites in zeolite pores promote the dissociation of N₂O₄ intermediates into NO⁺ and NO₃^– species with a low activation barrier (15 kJ mol^–1). Moreover, the computed activation barrier for the reduction of NO⁺ species by NH₃ was considerably low (6 kJ mol^–1). The experimental and theoretical results of this study demonstrate the high potential of Cu-free H-CHA zeolites for promoting lean NO_x capture to form NO⁺ species and the subsequent reduction by NH₃ at room temperature.

中文翻译：

---

贫NO _X捕捉和还原NH ₃经由NO ⁺中间体较H-CHA在室温

结合原位红外光谱和密度泛函理论（DFT ），研究了质子型菱沸石（H-CHA）上NO氧化为NO ₂以及随后通过NO ⁺中间体被NH ₃还原的过程。）计算。该原位IR光谱结果表明，NO ⁺ NO + O流下形成物种₂在27-250℃下更稳定的在较低温度下在两个H-CHA和铜阳离子交换的沸石CHA（CU-CHA ）。阿累尼乌斯图（T = 27–120°C）显示了形成NO的负表观活化势垒能（−11.5 kJ mol ^–1）NO + O ₂下的⁺物质流过H-CHA。在27℃下示出了IR光谱的时间过程的NO被O氧化₂至NO ₂，然后进一步转化经由Ñ ₂ Ò ₄为NO ⁺与NO ₃ ^- 。随后在27°C下暴露于NH _3中，会将NO ⁺物种还原为N ₂。DFT计算表明，在沸石孔布朗斯台德酸位点促进N的离解₂ ö _4个中间体成NO ⁺与NO ₃ ^-具有低激活势垒（15 kJ mol ^–1）的物种。此外，计算得出的通过NH ₃还原NO ⁺物种的活化势垒非常低（6 kJ mol ^–1）。本研究的实验和理论结果表明用于促进贫NO铜-自由H-CHA沸石的高电位_X捕获以形成NO ⁺物种和由NH随后的还原₃在室温下。