Abstract:

The effect of gas phase O 2, reversibly adsorbed oxygen and the surface state of Ni/Al 2O 3 catalyst on the decomposition of CH 4 and partial oxidation of CH 4 were studied using transient response technique at atmospheric pressure and 700 ℃. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H 2 can be produced from non-selective oxidization of CH 4 by reversibly adsorbed oxygen which is more active in oxidizing CH 4 completely than NiO via Rideal-Eley mechanism and both the conversions of CH 4 and O 2 and the selectivities to CO and H 2 are very low. Therefore, keeping the catalyst surface in the reduction state is the prerequi sation of high conversion of CH 4 and high selectivities to CO and H 2.The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH 4. During partial oxidation of CH 4, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduction state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH 4, and indirect oxidation mechanism is impossible to gain dominance in the reaction under the experimental conditions. 

Key words: Methane, Partial oxidation, Syngas, Ni/Al2O3, Surface state