The partial oxidation of CH4 was studied using a commercial Ni/α-Al2O3 catalyst. The results show that two operating regimes can be maintained: a low-conversion regime where CO2 and H2O are formed and a high-conversion regime where CO, CO2, H2 and H2O are formed. The latter regime is established by "catalytic light-off" which among other conditions depends on temperature, feed composition and catalyst activity. Prior to light-off, the catalyst is in the NiO form. Following light-off, the catalyst is in NiO form near the inlet and metallic form further downstream. A series of NiO/α-Al2O3, and NiO/ZrO2 catalysts were prepared by impregnation and calcination in air between 750 and 1050°C. These catalysts were characterized by the BET method, O2 chemisorption, X-ray diffraction, electron microscopy and ESCA. Test analyses indicate that the supported NiO particles are made up of a large number of small crystallites which become more dispersed after reduction and reunite after oxidation. The activity of these catalysts for CH4 oxidation under pre-light-off conditions was found to decrease dramatically with increasing calcination temperature. However, the calcined catalysts can be reactivated by reduction in H2 prior to reaction. The change in activity is attributed mainly to the change in specific activity of NiO which is explained in terms of the change in excess oxygen content.
