Investigation of the degradation mechanism of catalytic wires during oxidation of ammonia process

Pura, Jarosław; Wieciński, Piotr; Kwaśniak, Piotr; Zwolińska, Marta; Garbacz, Halina; Zdunek, Joanna; Laskowski, Z.; Gierej, Maciej

doi:10.1016/j.apsusc.2016.05.071

Cited by 9 publications

(7 citation statements)

References 8 publications

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“…Since the invention of the Pd-based gauzes for Pt-catchment in the late 1960s [5], several studies on their performance and degradation behaviour are reported [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Surprisingly, its behaviour is completely opposite to the expectations of a noble metal heated at high temperature; a huge increase in surface area is observed rather than sintering and grain growth (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Mechanism of grain reconstruction of Pd and Pd/Ni wires during Pt–catchment

et al. 2022

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Section: Introductionmentioning

confidence: 99%

Mechanism of grain reconstruction of Pd and Pd/Ni wires during Pt–catchment

et al. 2022

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“…The clearly diminished wire diameter after 50 days of operation shows substantial and progressive material loss with time on stream. However, and as observed in previous literature studies, 13,23 it is not possible to state purely from shape analysis alone whether only surface diffusion or also volume diffusion plays a role. This was later analyzed with resonant STXM-CT by quantifying the local Pt and Rh composition.…”

Section: Resultsmentioning

confidence: 78%

“…21,22 Laboratory X-ray CT has previously visualized degradation and bulk PGM loss in Pt/Rh gauzes in terms of surface geometry, but without any information regarding chemical composition. 23 Recently, the surface degradation of Pd-based catchment gauzes was visualized using in situ synchrotron X-ray CT in absorption-contrast under model aging conditions in air. Quantitative composition changes could not be retrieved in these gauzes due to the phasecontrast artifacts resulting in an artificial intensity profile within the wire.…”

Section: Introductionmentioning

confidence: 99%

“…As an alternative, hard X-ray tomography (X-ray CT) can offer noninvasive 3D imaging of physical and chemical structures in complex solids, including technical or industrial catalysts. , Laboratory X-ray CT has previously visualized degradation and bulk PGM loss in Pt/Rh gauzes in terms of surface geometry, but without any information regarding chemical composition . Recently, the surface degradation of Pd-based catchment gauzes was visualized using in situ synchrotron X-ray CT in absorption-contrast under model aging conditions in air.…”

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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“…%) alloy to be selected as the industrial Pt-catchment system. Since then, several studies have been performed on both Pd/Au and the more recent Pd/M (M = Co, Ni, Cu) systems. ,,− The latest studies on Pd and Pd/Ni (91/9 at. %) wires showed that the pore formation observed during industrial operation originates from two different phenomena: (1) thermal etching related to extreme gas/temperature conditions, giving a rounded crystallite shape and (2) grain reconstruction during Pt-catchment giving an edged crystallite shape .…”

Section: Introductionmentioning

confidence: 99%

Pt-Catchment Using Pd/Au Alloys: Effect of Enhanced Diffusion

Fjellvåg

Waller

et al. 2023

Ind. Eng. Chem. Res.

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We have studied a series of Pd/Au alloys as Pt-catchment materials, both in lab-scale experiments and in an industrial ammonia oxidation plant. Our focus has been on how bulk Pt diffusion affects grain reconstruction in Pd/Au alloys (91/9 and 50/50 at. %) during Pt-catchment, performed by studying both polycrystalline (as produced) and quasi-monocrystalline (preannealed in vacuum) wires. The grain reconstruction is reduced when alloying Pd with Au, and it is almost absent for Pd/Au (50/50 at. %). For all Pd-containing samples with a quasi-monocrystalline grain structure, the restructuring is limited in short (<20 days) laboratory experiments but present in the 5 month industrial experiment. Notably, the Pd/Au (50/50 at. %) alloy shows a low degree of restructuring in all experiments but a reduced Pt-catchment in the industrial experiment. The mechanism for grain reconstruction of Pd/Au alloys is discussed, along with the role of the Kirkendall effect and the internal porosity on wire restructuring.

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Investigation of the degradation mechanism of catalytic wires during oxidation of ammonia process

Cited by 9 publications

References 8 publications

Mechanism of grain reconstruction of Pd and Pd/Ni wires during Pt–catchment

Mechanism of grain reconstruction of Pd and Pd/Ni wires during Pt–catchment

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

Pt-Catchment Using Pd/Au Alloys: Effect of Enhanced Diffusion

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