Origin of temperature oscillations of nickel catalyst occurring in methane oxidation

A. A. Saraev, S. S. Kosolobov, V. V. Kaichev, V. I. Bukhtiyarov

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

The catalytic oxidation of methane over a nickel foil has been investigated in a wide range of methane: oxygen molar ratios at a constant reactor temperature of 680°C. Under oxygen-deficient conditions, the reaction takes place in the self-oscillating mode. Stable self-sustained oscillations of the methane oxidation rate are observed in the CH4: O2 molar ratio range from 2: 1 to 19: 1. This process is accompanied by catalyst temperature oscillations, whose amplitude reaches 80°C. It has been demonstrated by scanning electron microscopy that the origination of the self-sustained oscillations is accompanied by morphological changes in the catalyst surface. Under the action of the reaction medium, a porous layer 5-10 μm in thickness forms on the nickel foil surface. The mechanism of methane oxidation over nickel that accounts for the onset of the self-sustained oscillations is discussed. This mechanism is based on periodical nickel oxidation and reduction. When nickel is in the high-activity state, it is mainly in metallic form, and the passage of nickel into its low-activity state is accompanied by the formation of a nickel oxide layer on the foil surface. The reduction of this nickel oxide causes a periodic decrease in the catalyst temperature. The total and partial oxidations of methane on the reduced surface of the nickel foil raise the catalyst temperature. Under oxygen-deficient conditions, a carbon deposit builds up on the catalyst surface, and the combustion of this deposit complicates the catalyst temperature oscillation profile.

Original languageEnglish
Pages (from-to)598-604
Number of pages7
JournalKinetics and Catalysis
Volume56
Issue number5
DOIs
Publication statusPublished - 30 Sep 2015
Externally publishedYes

Keywords

  • methane oxidation
  • nickel catalysts
  • oxidation mechanism
  • temperature oscillations

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