Catalytic Activity and Deactivation Mechanisms of Supported NiO in CH4 Oxidation

Citation

Phichitkul, Charunya (1981) Catalytic Activity and Deactivation Mechanisms of Supported NiO in CH4 Oxidation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kmv4-kb66. https://resolver.caltech.edu/CaltechETD:etd-10042006-154422

Abstract

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.

Thesis Files