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Abstract <p>High-temperature oxidation of NH<sub>3</sub> with air to NO oxide on platinum alloy gauzes is used in the industrial production of nitric acid, which is employed to manufacture agricultural fertilizers. To enhance the efficiency of the catalytic gauzes, particular attention is paid to the etching processes initiated by the oxidation of NH<sub>3</sub> on platinum group metals (PGMs) and their alloys. In this study, high-resolution scanning electron microscopy (HR SEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS) were used to investigate and characterize microrelief, morphology, structure, and chemical composition of the etching structures on Pt(poly) after NH<sub>3</sub> oxidation with air at <i>Т</i> = 1133 K and a pressure of 3.6 bar. A microgranular structure with 50−150 µm grains having different etching structures was detected on the Pt(poly) surface. Crystal growth pyramids about 80 nm in height were observed on the surface of grains with decreased etching and surface structure close to {111} faces. On the surface of grains with increased etching and surface structure close to {100} and {110} faces, we detected etch pits represented by regular, similarly oriented etch grooves with the dimensions (length × width × depth) of 3.0 × 0.7 × 0.35 µm. The etching structures contained Pt, Fe, Si, Al, Mg, O, N, and C. The elements Pt, O, and C had high concentrations (12.2–53.7 at %), while the other elements had low ones (0.1−4.8 at %). The analysis of the chemical composition of surface and subsurface layers of the catalyst showed that the detected О and N atoms were absorbed on defects and gradually accumulated in subsurface Pt layers during NH<sub>3</sub> oxidation. Oxide particles with a size of ~100 nm containing Fe<sub>2</sub>O<sub>3</sub>, MgO, and SiO<sub>2</sub>, which were observed at the vertices of pyramids and inside the etch grooves, can be formed in the oxidizing medium from Fe, Si, and Mg impurities that moved to the catalyst from the flow of reagents and from the reactor during NH<sub>3</sub> oxidation. These oxide particles can be involved in the etching processes on platinum alloy catalysts under the conditions of NH<sub>3</sub> oxidation.</p>

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Formation of Etching Structures on the Surface of Polycrystalline Platinum in the Course of Catalytic Oxidation of Ammonia with Air at 1133 K

  • 期刊论文

  • 发表日期：

    2025年2月1日

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  • A. N. Salanov,
  • A. N. Serkova,
  • A. S. Zhirnova,
  • L. A. Isupova,
  • V. N. Parmon

摘要

Abstract

High-temperature oxidation of NH3 with air to NO oxide on platinum alloy gauzes is used in the industrial production of nitric acid, which is employed to manufacture agricultural fertilizers. To enhance the efficiency of the catalytic gauzes, particular attention is paid to the etching processes initiated by the oxidation of NH3 on platinum group metals (PGMs) and their alloys. In this study, high-resolution scanning electron microscopy (HR SEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS) were used to investigate and characterize microrelief, morphology, structure, and chemical composition of the etching structures on Pt(poly) after NH3 oxidation with air at Т = 1133 K and a pressure of 3.6 bar. A microgranular structure with 50−150 µm grains having different etching structures was detected on the Pt(poly) surface. Crystal growth pyramids about 80 nm in height were observed on the surface of grains with decreased etching and surface structure close to {111} faces. On the surface of grains with increased etching and surface structure close to {100} and {110} faces, we detected etch pits represented by regular, similarly oriented etch grooves with the dimensions (length × width × depth) of 3.0 × 0.7 × 0.35 µm. The etching structures contained Pt, Fe, Si, Al, Mg, O, N, and C. The elements Pt, O, and C had high concentrations (12.2–53.7 at %), while the other elements had low ones (0.1−4.8 at %). The analysis of the chemical composition of surface and subsurface layers of the catalyst showed that the detected О and N atoms were absorbed on defects and gradually accumulated in subsurface Pt layers during NH3 oxidation. Oxide particles with a size of ~100 nm containing Fe2O3, MgO, and SiO2, which were observed at the vertices of pyramids and inside the etch grooves, can be formed in the oxidizing medium from Fe, Si, and Mg impurities that moved to the catalyst from the flow of reagents and from the reactor during NH3 oxidation. These oxide particles can be involved in the etching processes on platinum alloy catalysts under the conditions of NH3 oxidation.