Abstract

The local chemical composition of the most characteristic regions of a rough etched layer on the front side of the Pt–Pd–Rh–Ru gauze with a composition of 81, 15, 3.5, 0.5 wt %, respectively, after the oxidation of NH₃ with air at Т = 1133 K and a pressure of 3.6 bar was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The local chemical composition of the grain surface in the low etching region, on porous crystal agglomerates (cauliflowers) in the etched layer, and between cauliflowers at the bottom of pore voids was determined. Pt, Pd, Rh, Ru, C, O, and N were recorded on grains, cauliflowers, ​​and pore bottom, which had different defect concentrations and temperatures. The metal contents on the grains and at the bottom of pore voids coincided with the composition given by the gauze manufacturer, whereas cauliflowers had a higher Rh content (12.6 at %). Reliable quantitative data on the contents of O_ab and N_ab atoms in the subsurface layers of grains, cauliflowers, ​​and pore bottom were obtained for the first time: 18.6, 7.3, and 10.4 at % for О_ab and 17.1, 16.8, and 33.6 at % for N_ab, respectively. The maximum content of O_ab atoms (18.6 at %) was recorded in defect regions with low temperature (grains in the low etching region), while increased content of N_ab atoms (33.6 at %) was found in regions with low defect concentrations but elevated temperature (pore voids). These data on the O_ab and N_ab contents in regions with different degrees of defectiveness and temperatures made it possible to reveal for the first time the types of defects on which predominantly the O and N atoms penetrate into the catalyst during NH₃ oxidation. The O_ab and N_ab atoms accumulate in the subsurface layers of the Pt–Pd–Rh–Ru metal alloy during intercalation of O atoms on the grain boundaries and in etch pits and penetration of N atoms into the lattice of the alloy. The reported dissolution model of O and N atoms in the subsurface region of the catalyst will provide deeper understanding of the mechanism of NH₃ oxidation that forms NO oxide and of the related etching process.

中文翻译：

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NH3 在 1133 K 氧化后，Pt-Pd-Rh-Ru 纱布上的颗粒表面、花椰菜和孔隙的局部化学分析

摘要

NH ₃氧化后，Pt-Pd-Rh-Ru 纱网正面粗蚀刻层最特征区域的局部化学成分，其成分分别为 81、15、3.5、0.5 wt %空气在Т= 1133 K 和 3.6 bar 的压力通过扫描电子显微镜和能量色散 X 射线光谱进行了研究。确定了低蚀刻区域中、蚀刻层中多孔晶体团块（花椰菜）上以及孔隙底部花椰菜之间的晶粒表面的局部化学成分。Pt、Pd、Rh、Ru、C、O和N被记录在具有不同缺陷浓度和温度的谷物、花椰菜和孔底上。颗粒上和孔隙底部的金属含量与纱布制造商提供的成分一致，而花椰菜的 Rh 含量更高（12.6 at %）。O _ab和 N _ab含量的可靠定量数据首次获得了谷物、花椰菜和孔底亚表层中的原子：О _{ab 分别}为 18.6、7.3 和 10.4 at %，N _ab分别为 17.1、16.8和 33.6 at % 。O _ab原子的最大含量（18.6 at %）记录在低温缺陷区域（低蚀刻区域中的晶粒），而在低缺陷浓度的区域中发现N _ab原子的含量增加（33.6 at %），但升高的温度（孔隙）。这些关于 O _ab和 N _{ab 的数据}具有不同缺陷程度和温度的区域中的含量使得有可能首次揭示在 NH ₃氧化过程中主要是 O 和 N 原子渗入催化剂的缺陷类型。O _ab和 N _ab原子在 Pt-Pd-Rh-Ru 金属合金的亚表面层中积累，过程中 O 原子在晶界和蚀刻坑中的嵌入以及 N 原子渗透到合金的晶格中。报告的催化剂表面下区域中 O 和 N 原子的溶解模型将提供对形成 NO 氧化物的 NH ₃氧化机制和相关蚀刻过程的更深入理解。