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Zhang, Xunli; Mingos, D. Michael P.; Hayward, D.

doi:10.1023/a:1009036128275

Cited by 43 publications

(13 citation statements)

References 30 publications

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“…Such oscillations have been observed over palladium catalysts [1][2][3][4], and supported nickel catalysts [5][6][7]. It has been observed in our earlier study that chromel/alumel thermocouple wires and nickels wires can also catalyse the methane/oxygen reaction and result in rate oscillations [8].…”

Section: Introductionsupporting

confidence: 54%

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Zhang

Lee

Mingos

et al. 2003

Applied Catalysis A: General

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Oscillatory reactions over palladium foil and wire catalysts during the oxidation of methane have been investigated over a wide range of reaction temperatures and argon/methane/oxygen feed gas compositions. Characterisation of the catalyst has also been carried out using scanning electron microscopy (SEM) techniques, which revealed the presence of a porous surface. This suggested that the metal surface has undergone a change since the reaction commenced, and using X-ray powder diffraction (XRD) techniques the palladium phase was shown to be the dominant phase present. Hysteresis phenomena were observed in the activity of the reaction as the temperature was cycled up and down, showing that the metal surface was continually changing throughout the reaction. The activation energies of the reaction during the high reactivity mode, PdO, and low reactivity mode, Pd, were also calculated. Oscillation rates were observed to depend on the dominant surface. Oscillations were frequent when the high reactivity mode was dominant while the activation energy of this mode was found to be low. When the low reactivity mode was dominant, the oscillations were slower and the activation energy was three times larger. The results obtained imply that the behaviour of the palladium surface, switching back and forth from the reduced state to the oxidised state, is responsible for the oscillatory behaviour seen in this system.

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Section: Introductionsupporting

confidence: 54%

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Zhang

Lee

Mingos

et al. 2003

Applied Catalysis A: General

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“…Our previous studies showed that chromel-alumel thermocouples, when no other catalyst was present, can act as effective catalysts for the methane/oxygen reaction oscillating at temperatures between 700 and 740 • C, where nickel was found to be the active ingredient [11]. In this paper we report the first observation of oscillations over cobalt wire/foil metal catalysts when an argon/methane/oxygen mixture was passed and the further investigations into the oscillatory reaction kinetics.…”

Section: Introductionmentioning

confidence: 71%

“…These oscillations can be distinguished from those occurring on the chromel-alumel thermocouple wires because they generally occurred in a higher temperature range and the change in temperature during oscillations was much greater. The unsheathed thermocouple wires produced oscillations at around 700 • C with a temperature change of only 7-8 • C [11]. In the experiments described here, the thermocouple wires were sheathed to within a few millimetres of the junction of the cobalt wire or foil and access to reaction gases was therefore greatly restricted.…”

Section: General Observation On the Oscillation Of Methane Oxidation mentioning

confidence: 99%

Oscillatory behaviour during the partial oxidation of methane over cobalt wires and foils

Zhang

Lee

Mingos

et al. 2003

Applied Catalysis A: General

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The oscillatory behaviour over cobalt wire and foil catalysts was examined at atmospheric pressure under various reaction temperatures and argon/methane/oxygen feed gas compositions for the partial oxidation of methane. Rough and porous oxide layers on the catalyst surface were confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The results obtained from the experimental studies indicated that the oscillatory behaviour exhibited during methane oxidation was related to the behaviour of the catalyst surface switching back and forth from the reduced state to the oxidised state. The reduction of the oxide layer followed by the almost immediate re-oxidation of the metal can be accounted for only if the oxide layer formed by oxidation is different from the oxide layer existing during reduction.

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“…Our previous study showed that chromel-alumel thermocouples, when no other catalyst was present, can act as eective catalysts for the methane/oxygen reaction oscillating at temperatures between 700 and 740 8C, and nickel was identi®ed as the active catalyst [16]. In this paper we report on the further investigation into the oscillatory reaction kinetics over nickel foils during the reaction of oxidation of methane.…”

Section: Introductionmentioning

confidence: 90%

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2002

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The study of the partial oxidation of methane over nickel foils has been carried out over a wide range of reactor temperatures (748± 930 8C) and feed-gas compositions (Ar/CH 4 /O 2 ), ranging from 30 : 29 : 1 to 30 : 12 : 18 cm 3 min ÿ1 at atmospheric pressure. The product formation shows pronounced oscillations. A modi®ed thermocouple was designed to measure the temperature while the interposed nickel foil worked as a catalyst. The oscillations have been attributed to the cyclic reduction and oxidation of the nickel surface in the speci®c reaction environment at elevated temperatures.

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Cited by 43 publications

References 30 publications

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Oscillatory behaviour during the partial oxidation of methane over cobalt wires and foils

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