Oscillatory Behavior during the Catalytic Partial Oxidation of Methane: Following Dynamic Structural Changes of Palladium Using the QEXAFS Technique

Stötzel, Jan; Frahm, R.; Kimmerle, Bertram; Nachtegaal, Maarten; Grunwaldt, Jan‐Dierk

doi:10.1021/jp2052294

Cited by 48 publications

(44 citation statements)

References 76 publications

(128 reference statements)

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“…Recently, it has been confirmed directly by the results of in situ studies [25][26][27]. However, the reasons that initiate the appearance of these oscillations are not clear yet.…”

Section: Introductionmentioning

confidence: 85%

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Каичев

Teschner

Saraev

et al. 2016

Journal of Catalysis

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The evolution of self-sustained reaction-rate oscillations in the catalytic oxidation of propane over a nickel foil has been studied in situ using X-ray photoelectron spectroscopy coupled with on line mass spectrometry and gas chromatography. Changes in the effective surface area and in the catalyst morphology under reaction conditions have been examined by scanning electron microscopy and a krypton adsorption technique. It is shown that the regular kinetic oscillations arise under oxygen-lean conditions. CO, CO 2 , H 2 , H 2 O, and propylene are detected as products.The conversion of propane oscillates in a range from 1% to 23%. During the half-periods with high activity, the main reaction pathway is the partial oxidation of propane: selectivity toward CO achieves 98%. In contrast, during the half-periods with low activity, the reaction proceeds through three competitive pathways: the partial oxidation of propane, the total oxidation of propane, and the dehydrogenation of propane to propylene. The driving force for the selfsustained kinetic oscillations is the periodic reoxidation of nickel. According to the Ni2p and O1s core-level spectra measured in situ, the high-active catalyst surface is represented by metallic nickel, whereas during the inactive half-periods the catalyst surface is covered with a thick layer of NiO. The intensity of O1s spectra follows the oscillations of O 2 in the gas phase during the oxidation of propane. It is found that during the induction period before the regular oscillations appear, a rough and porous structure develops because of strong reconstruction of the catalyst surface. The thickness of the reconstructed layer is approximately 10-20 µm. This process is accompanied with at least an 80-fold increase in the effective surface area compared with a clean, non-treated nickel foil, which undoubtedly leads to a drastic increase in the number of active sites. We believe that it is the main reason for the induction period always being  Corresponding author.E-mail address: vvk@catalysis.ru (V.V. Kaichev) 2 observed before the appearance of self-sustained oscillations in the catalytic oxidation of light hydrocarbons over catalysts with a low specific surface area (single crystals, foils, or wires).Moreover, without such reconstruction, the oscillations cannot arise due to low activity of such catalysts.

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“…Recently, it has been confirmed directly by the results of in situ studies [25][26][27]. However, the reasons that initiate the appearance of these oscillations are not clear yet.…”

Section: Introductionmentioning

confidence: 85%

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Каичев

Teschner

Saraev

et al. 2016

Journal of Catalysis

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“…However, this is in contradiction to surface scientific studies [63,64,73,74], modeling studies [75,76], the observation of a beneficial effect of H 2 during CO oxidation [76] and also to a very recent ETEM study which ascribed increased activity to metallic nanoparticles [54]. Moreover, structural heterogeneities along the catalyst bed were revealed lately, which were also observed during noble metal catalyzed partial oxidation of methane [28,77,78].…”

Section: Introductionmentioning

confidence: 90%

Operando spatially and time-resolved X-ray absorption spectroscopy and infrared thermography during oscillatory CO oxidation

Gänzler

Casapu

Boubnov

et al. 2015

Journal of Catalysis

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117

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“…Other systems that have been studied under transient reaction conditions are, e.g., the Fischer-Tropsch reaction, where the influence of unsteady state conditions on the process itself was investigated [7,8,27]. Various spectroscopic, microscopic and diffraction techniques applied under reaction conditions revealed different structural changes of catalysts used in processes operated under changing reaction atmospheres [28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO2

et al. 2017

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Abstract:The methanation of CO 2 within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al 2 O 3 catalyst with uniform 3.7 nm metal particles and a dispersion of 21% suitable to investigate structural changes also in a surface-sensitive way was prepared and characterized in detail. Operando quick-scanning X-ray absorption spectroscopy (XAS/QEXAFS) studies were performed to analyze the influence of 30 s and 300 s H 2 interruptions during the methanation of CO 2 in the presence of O 2 impurities (technical CO 2 ). These conditions represent the fluctuating supply of H 2 from renewable energies for the decentralized methanation. Short-term H 2 interruptions led to oxidation of the most reactive low-coordinated metallic Ni sites, which could not be re-reduced fully during the subsequent methanation cycle and accordingly caused deactivation. Detailed evaluation of the extended X-ray absorption fine structure (EXAFS) spectra showed surface oxidation/reduction processes, whereas the core of the Ni particles remained reduced. The 300-s H 2 interruptions resulted in bulk oxidation already after the first cycle and a more pronounced deactivation. These results clearly show the importance and opportunities of investigating the structural dynamics of catalysts to identify their mechanism, especially in power-to-chemicals processes using renewable H 2 .

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Oscillatory Behavior during the Catalytic Partial Oxidation of Methane: Following Dynamic Structural Changes of Palladium Using the QEXAFS Technique

Cited by 48 publications

References 76 publications

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

Operando spatially and time-resolved X-ray absorption spectroscopy and infrared thermography during oscillatory CO oxidation

Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO2

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