Study of nickel catalyst in oscillating regime of methane oxidation by means of gravimetry and mass-spectrometry

The application of the thermogravimetric analysis (TGA) combined with on-line mass-spectrometry analysis of the effluent gas mixture from the reactor and temperature programmed reduction (TPR) experiments allowed to obtain information about the content of oxygen and carbon in Ni catalysts during the oscillatory behaviour of methane oxidation. It was demonstrated that the significant variation of the oxygen content (several tens layers) in the Ni catalyst occurred during the oscillatory behaviour of methane oxidation. Together with the visual observation of the color changes due to the periodic variation of the Ni valence these data prove that the oxidation-reduction processes play the crucial role in the origin of the oscillatory behaviour during the methane oxidation over Ni catalysts. It was shown that during oscillatory behaviour of methane oxidation the catalyst contains the significant amount of deposited carbon, at least, in two different forms. One of them is characterised by the higher reactivity and probably the higher state of the distribution on a metallic surface. The higher activity form of carbon prevails in the reduced state of the nickel catalyst. Another carbon form is characterised by the lower reactivity and, likely, does not noticeably effect the oscillations during methane oxidation. (c) 2006 Elsevier B.V. All rights reserved.