Resolving gradients in an ammonia oxidation reactor under industrial conditions: A combined experimental and simulation study

Pottbacker, Jan; Jakobtorweihen, Sven; Behnecke, Anna Sophia; Abdullah, Adnan; Özdemir, Melis; Warner, Maximilian; Menon, Mohan; Bujalski, Jakub Michał; Waller, David; Korup, Oliver; Horn, Raimund

doi:10.1016/j.cej.2022.135350

Cited by 7 publications

(6 citation statements)

References 38 publications

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“…The latter was calculated from computational fluid dynamics modeling in previous work. 31 However, the subsequent decrease in surface area after 50 days on stream can be attributed to the widespread breakage of protrusions from the surface. This can also be observed by the rugged texture of the wire surface, with only a few large protrusions present (Figure 2a).…”

Section: Resultsmentioning

confidence: 99%

“…The effect of degradation on the catalyst surface area was studied for a cropped volume of 29 μm, showing an increased surface area of the aged gauzes by a factor of 4–6 compared to the fresh gauze (Table and SI section 3.2). The latter was calculated from computational fluid dynamics modeling in previous work . However, the subsequent decrease in surface area after 50 days on stream can be attributed to the widespread breakage of protrusions from the surface.…”

Section: Resultsmentioning

confidence: 99%

“…Fresh Pt/Rh gauzes (∼76 μm wire diameter, 5 wt % Rh) were provided by Yara International ASA (Oslo, Norway). Aging was performed under typical industrial NH 3 oxidation conditions in a bench-scale reactor at TUHH at an absolute pressure of 5 bar, inlet temperature of 300 °C, and feed composition of NH 3 /O 2 /Ar/N 2 = 10/18.6/2/69.4 mol % . Gauzes were removed from the reactor after 24, 50, and 100 h aging time.…”

Section: Methodsmentioning

confidence: 99%

“…Aging was performed under typical industrial NH 3 oxidation conditions in a bench-scale reactor at TUHH at an absolute pressure of 5 bar, inlet temperature of 300 °C, and feed composition of NH 3 /O 2 /Ar/N 2 = 10/18.6/ 2/69.4 mol %. 31 Gauzes were removed from the reactor after 24, 50, and 100 h aging time. The first gauze (toward the inlet) from a treated stack of 10 gauzes was chosen due to an expected higher degree of degradation from exposure to a maximum concentration of NH 3 and O 2 .…”

Section: Sample Preparationmentioning

confidence: 99%

“…STXM-CT recorded using a single-photon counting detector enabled visualization and quantification of the local elemental distribution of Pt and Rh via the Beer−Lambert law. By performing resonant STXM-CT above and below the Rh Kedge (Figure 1), regions of Pt loss and Rh segregation were observed locally (∼2 μm resolution) for typical Pt/Rh gauze catalysts aged under industrial NH 3 oxidation conditions for 24 to 100 h in a bench-scale reactor 31 and up to 50 days in a pilot plant. This quantitative study of local compositional changes can specify the extent of Pt loss and Rh segregation leading to a redistribution of metals with advanced aging.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative Chemical Mapping of Pt/Rh Gauze Catalysts for Ammonia Oxidation using Resonant X-ray Tomography

Das,

Stuckelberger,

Pottbacker

et al. 2024

J. Phys. Chem. C

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The loss of platinum group metals during the industrial Ostwald process for catalytic ammonia oxidation is a century-old concern. Understanding catalyst degradation requires knowledge of physicochemical changes occurring on stream, particularly on technical Pt/Rh gauze catalysts. However, such catalysts are mainly studied with surface-sensitive methods or as model systems since their composition of noble metals (e.g., 95/5 wt % Pt/Rh) makes it challenging to characterize the bulk catalyst. Here, we exploit the high-resolution and elemental sensitivity of synchrotron-based hard X-ray resonant tomography to quantify the 3D distribution of Rh and Pt in technical gauze catalysts. Resonant tomography performed above and below the Rh K-edge (23.300 and 23.208 keV, respectively) allowed computation of elemental distribution. Absorption contrast tomography was successful despite beam transmission of <0.1%. This was achieved using a single-photon counting detector. Rh segregation, Pt loss, and bulk material degradation leading to redistribution of elements were visualized and quantified within intact ∼76 μm diameter wires, with 2 μm resolution, and up to 50 days on stream. The estimated local Pt and Rh wt % changes showed significant material loss from the wire exterior and characteristic protrusions. However, the wire core was unaffected by the reaction conditions even after 50 days on stream. No volume diffusion from the wire center to the exterior was observed to mitigate material loss from the latter. This flexible and high-throughput quantitative imaging approach is uniquely possible with synchrotron hard X-ray tomography, opening further routes of study for compositionally challenging industrial catalysts.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Sample Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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