Effect of redox treatment on methane oxidation over binary catalyst

Abstract

This chapter discusses the oxidative transformations of methane with a catalyst system that combines an oxide and a metal component. The presence of both components gave rise to complex oscillation phenomena. The influence of pretreatment and reaction conditions over a wide range of parameters on the oscillatory process was studied. The possible role of mass transfer and the balance of heat in the reactor were analyzed and a model for the role of the components in the binary catalyst system is suggested. A chromel–alumel thermocouple (diameter 0.3 mm, sheathed in a quartz cover or bare) was placed co-axially into the reactor filled with oxide catalyst, making it possible to detect temperature oscillations, accompanying concentration oscillations. This thermocouple in bare form also acts as the metal component in the oxide-metal binary system. The surface area of the thermocouple filament is ∼ 7.5x10 -5 m -2 . The effect of the state of the surface on the kinetic behavior was studied, using various feeder, including the methane-oxygen mixture alternating with inert (He), oxidizing (O 2 ), and reducing (H 2 ) gases. If the oxide component is removed from the reactor, no conversion of reactants is observed, indicating a very low activity of the metal filament in methane oxidation. No reaction occurs also when ethane is added to the methane–oxygen mixture. Oxidation of methane in the presence of such a binary oxide-metal catalyst proceeds in an oscillatory regime and both temperature and concentration oscillations take place. Oscillations arise at the temperature at which the rate of reaction over the oxide component becomes noticeable (∼500 °C).