Investigation of Ce/BEA as a passive NOx adsorber: 2. Hydrothermal aging deactivation mechanism

IF 5.2 1区化学 Q1 CHEMISTRY, APPLIED Journal of Rare Earths Pub Date : 2024-08-01 DOI:10.1016/j.jre.2023.05.009

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Abstract

Ce/BEA has the potential to be applied as a novel passive NO_x absorber (PNA) in the after-treatment of vehicles due to its considerable NO_x storage capacity. However, as a vehicle exhaust after-treatment material, it must withstand the test of long-term hydrothermal aging. This work examined the deactivation mechanism of Ce/BEA during hydrothermal aging. 3.0 wt% Ce/BEA was prepared using the ion-exchange method, and then subjected to hydrothermal treatment at 650 °C with 10% H₂O for 1–12 h to obtain samples with different aging extent. For comparison, the H-BEA support was aged under the same conditions. Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), NH₃ temperature programmed reduction (NH₃-TPD), ²⁷Al MAS nuclear magnetic resonance (²⁷Al MAS NMR), H₂ temperature programmed reduction (H₂-TPR), and high resolution-transmission electron microscopy (HR-TEM) were performed to characterize the changes in PNA performance, structure, Ce species, and acidity. The HR-TEM and H₂-TPR results show that CeO_x particles appear after hydrothermal aging, which results from the detachment and aggregation of active Ce species. Based on the ²⁷Al MAS NMR results, we conclude that BEA zeolite dealumination leads to the loss of acidic sites and the transformation of active Ce species on the acidic sites into the less active CeO_x. This is the primary reason for the hydrothermal aging deactivation of Ce/BEA.

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Ce/BEA作为NO被动吸附剂的研究：2。水热老化失活机理

Ce/BEA 具有相当大的氮氧化物储存能力，因此有潜力作为新型被动氮氧化物吸收剂（PNA）应用于汽车尾气后处理。然而，作为汽车尾气后处理材料，它必须经受长期水热老化的考验。本研究考察了 Ce/BEA 在水热老化过程中的失活机理。采用离子交换法制备了 3.0 wt% 的 Ce/BEA，然后在 650 ℃、10% H2O 的条件下进行 1-12 h 的水热处理，得到了不同老化程度的样品。为了进行比较，H-BEA 支撑物也在相同条件下进行了老化。实验采用了布鲁纳-艾美特-泰勒（BET）法、X 射线衍射（XRD）、NH3 温度编程还原（NH3-TPD）、27Al MAS 核磁共振（27Al MAS NMR）、H2 温度编程还原（H2-TPR）和高分辨率透射电子显微镜（HR-TEM）来表征 PNA 性能、结构、Ce 种类和酸度的变化。HR-TEM 和 H2-TPR 结果表明，水热老化后出现了 CeOx 颗粒，这是活性 Ce 物种脱离和聚集的结果。根据 27Al MAS NMR 结果，我们得出结论：BEA 沸石脱铝导致酸性位点丧失，酸性位点上的活性 Ce 物种转变为活性较低的 CeOx。这是 Ce/BEA 水热老化失活的主要原因。

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来源期刊

Journal of Rare Earths 化学-应用化学

CiteScore

8.70

自引率

14.30%

发文量

374

审稿时长

1.7 months

期刊介绍： The Journal of Rare Earths reports studies on the 17 rare earth elements. It is a unique English-language learned journal that publishes works on various aspects of basic theory and applied science in the field of rare earths (RE). The journal accepts original high-quality original research papers and review articles with inventive content, and complete experimental data. It represents high academic standards and new progress in the RE field. Due to the advantage of abundant RE resources of China, the research on RE develops very actively, and papers on the latest progress in this field emerge every year. It is not only an important resource in which technicians publish and obtain their latest research results on RE, but also an important way of reflecting the updated progress in RE research field. The Journal of Rare Earths covers all research and application of RE rare earths including spectroscopy, luminescence and phosphors, rare earth catalysis, magnetism and magnetic materials, advanced rare earth materials, RE chemistry & hydrometallurgy, RE metallography & pyrometallurgy, RE new materials, RE solid state physics & solid state chemistry, rare earth applications, RE analysis & test, RE geology & ore dressing, etc.