Decomposition of methane over Co3-xAlxO4 (x=0-2) coprecipitated catalysts: The role of Co phases in the activity and stability

High-purity hydrogen is an environmentally friendly source of alternative energy. Co3-xAl3O4 catalysts were evaluated for the production of H-2 through the catalytic decomposition of CH4. The catalysts were prepared by co-precipitation and characterized by N-2-physisorption analysis, TPR, XRD, and TPO. Activity tests were performed in a fixed bed tubular reactor. The samples were either reduced with H-2 at temperatures of 500 and 700 degrees C before the reactions or they were activated using CH4. Samples with Co/Al ratios of 1-2.3 showed higher surface area and exhibited the properties of mixed oxides derived from hydrotalcites. Six reducible phases were identified: three corresponding to the reduction of Co3O4 bulk oxide and three corresponding to mixed oxides represented by Co3-xAlxO4 with x varying from 0.5 to 2. The reduction temperature increased with x. The activation of the catalyst influenced the activity, the type of carbon produced, and the deactivation rate. Catalysts with Co/Al ratios of 1-2.3 showed the best results at 500 degrees C and required an induction time when they were activated with CH4. The stability of these catalysts was related to the Co3-xAlxO4 mixed oxides. The activation with H-2 at 700 degrees C caused excessive reduction of the Co3O4 phase, and all samples were deactivated by sintering in the reaction at 700 degrees C. For samples activated with CH4, the amount of amorphous carbon produced was more important than sintering for deactivation at 700 degrees C. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.