Self-oscillations of methane oxidation rate over Pd/Al2O3 catalysts: Role of Pd particle size

Bychkov, V. Yu.; Tulenin, Yu. P.; Slinko, M. M.; Khudorozhkov, Alexander K.; Bukhtiyarov, Valerii I.; Sokolov, Sergey; Корчак, В. Н.

doi:10.1016/j.catcom.2016.01.028

Cited by 14 publications

(10 citation statements)

References 25 publications

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“…However, recently, Bychkov and co-authors have studied the self-sustained reaction-rate oscillations in the oxidation of methane over Pd/Al 2 O 3 catalysts by thermogravimetry and mass spectrometry at ambient pressure. They have shown that the oscillations originated due to periodic oxidation and reduction of palladium, and crucially important, the maximum activity was observed on carbonized metallic Pd at least at 300–350 °C under methane-rich conditions . These contrasting conclusions provoked our further study of the oxidation of propylene over palladium at higher pressures in the same manner.…”

Section: Resultsmentioning

confidence: 99%

“…They have shown that the oscillations originated due to periodic oxidation and reduction of palladium, and crucially important, the maximum activity was observed on carbonized metallic Pd at least at 300−350 °C under methane-rich conditions. 19 These contrasting conclusions provoked our further study of the oxidation of propylene over palladium at higher pressures in the same manner. We repeated the TPRS-XPS study at nearambient pressure conditions, which allowed us to compare our results with the data obtained by thermogravimetry.…”

Section: Resultsmentioning

confidence: 99%

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In SituNAP-XPS and Mass Spectrometry Study of the Oxidation of Propylene over Palladium

et al. 2018

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The oxidation of propylene over a Pd(551) single crystal has been studied in the millibar pressure range using near-ambient pressure X-ray photoelectron spectroscopy and mass spectrometry. It has been shown that, irrespective of the O2/C3H6 molar ratio in the range 1–100, the total oxidation of propylene to CO2 and water and the partial oxidation of propylene to CO and H2 occur when the catalyst is heated above the light-off temperature; increasing the partial pressure of O2 leads to decreasing the catalytic activity. The selectivity toward CO2 is at least two times higher than the selectivity toward CO, indicating that the total oxidation is the main reaction route. The normal hysteresis with a light-off temperature higher than the extinction temperature is observed in the oxidation of propylene between 100 and 300 °C. According to NAP-XPS, the main reason for the hysteresis appearing is a competition between two surface processes: carbonization and oxidation of palladium. At low temperatures, the adsorption and following decomposition of propylene dominate, which results in accumulation of carbonaceous deposits blocking the palladium surface. Increasing the catalyst temperature leads to burning the carbonaceous deposits which initiates the following oxidation of propylene. The highest conversion of propylene is observed when both free surface sites and adsorbed oxygen atoms exist in a large amount on the catalyst surface. As the partial pressure of O2 increases, the catalyst surface gets covered by clusters of surface 2D palladium oxide, which is accompanied by a decrease in the catalytic activity. The mechanism of the oxidation of propylene over palladium is discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

In SituNAP-XPS and Mass Spectrometry Study of the Oxidation of Propylene over Palladium

et al. 2018

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“…Also, a strong dependence on the water content was found, that is, decrease of catalytic performance or even poisoning of the catalysts in the presence of water . Also the size of the PdO x particles seems to affect the CH 4 conversion heavily . Stakheev et al .…”

Section: Mechanism: Current Statusmentioning

confidence: 91%

Exploiting Synergies in Catalysis and Gas Sensing using Noble Metal‐Loaded Oxide Composites

et al. 2018

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Noble metal/metal oxide nanocomposites are very important in various fields of catalysis and play an evenly important role in gas sensing. Although there are many similarities regarding the choice of materials, the synthesis and the fundamental mechanisms, both research fields have been mostly treated independently up to now. In both fields, open questions regarding the elementary steps in the interaction of the gases with the active species and the role of the noble metal, the semiconducting metal oxide support and the interface remain. In this concept article, we first outline the importance of such composites in catalysis and gas sensing focussing on Pt/Pd, as well as CeO2 and SnO2 as transition metal oxides. Next, the state of art of both fundamental and relevant surface reactions and electronic mechanisms are described. Finally, we highlight the synergy of jointly exploring catalysis and gas sensing of noble metal/metal oxide nanocomposite materials and the benefit for both research fields if they are dealt with simultaneously using advanced characterization and operando methods, sophisticated preparation techniques, testing of the performance, and predictive theoretical modelling.

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“…These industrial processes necessarily perform at extremely high temperatures (>1000 °C) toward desirable product yield. Enormous efforts (e.g., altering supports, − control of metal particle-size, − and doping with heterometals − ) have been made to improve the performance of supported metal catalysts working under low-temperature conditions. It was found that downsizing the metal particle-size can significantly increase the activity in terms of methane activation and conversion. ,,− However, the supported metal catalysts are usually assembled by a broad particle size distribution, making it difficult to clearly distinguish the performances of size-specific metal particles.…”

Section: Introductionmentioning

confidence: 99%

Size-Dependent Reactivity of Rhodium Cluster Anions toward Methane

et al. 2019

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Metals are important industrial catalysts for activation and transformation of methane. Investigations on the reactivity evolution of metal particles along size change to determine the critical size at which the metal can exhibit excellent reactivity are helpful for design of efficient metal-based catalysts. Herein, the rhodium cluster anions Rh n – with n = 1–10 have been generated by the laser ablation method and a quadrupole mass filter has been used to mass-select cluster ions with a specific size for reacting with methane in an ion trap reactor under thermal collision conditions. The reactant and product ions have been detected by using a time-of-flight mass spectrometer. While the clusters of Rh2–6 – can react with a single methane molecule, giving rise to Rh n CH2 – ions, the dehydrogenation product is absent for the reaction systems of Rh1,7–10 – unless two or three CH4 molecules are coadsorbed. Reaction kinetics analysis demonstrates that although apparent oscillation of reaction rates appears across different sizes, the reactivity of Rh3 – and Rh4 – clusters is substantially higher than the smaller and larger ones by 2 or 3 orders of magnitude. The mechanistic aspects for the size-dependent reactivity of Rh n – have been discussed on the basis of quantum chemistry calculations.

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Self-oscillations of methane oxidation rate over Pd/Al2O3 catalysts: Role of Pd particle size

Cited by 14 publications

References 25 publications

In SituNAP-XPS and Mass Spectrometry Study of the Oxidation of Propylene over Palladium

In SituNAP-XPS and Mass Spectrometry Study of the Oxidation of Propylene over Palladium

Exploiting Synergies in Catalysis and Gas Sensing using Noble Metal‐Loaded Oxide Composites

Size-Dependent Reactivity of Rhodium Cluster Anions toward Methane

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