Production of COx Free Hydrogen and Nanocarbon via Methane Decomposition Over Unsupported Porous Nickel and Iron Catalysts

Abstract

Methane decomposition is the most effective method to produce greenhouse gas free hydrogen and nanocarbon. In this work, unsupported nickel and iron catalysts were successfully synthesized via a facile solid state citrate fusion method and used for the non-oxidative thermocatalytic decomposition of methane. The formation of phase pure crystalline structure of NiO and Fe2O3 with high surface porosity and improved textural properties was observed by various characterization techniques. The release of huge amount of gases from the bulk of the fused sample during the annealing process could result in the porosity. The catalysts exhibited high catalytic activity and stability for methane decomposition at three different reaction temperatures of 700, 800 and 900 °C without any catalyst deactivation. The yield of hydrogen and nanocarbon increased significantly with increasing the reaction temperature. A maximum hydrogen yield of 67% was obtained for the NiO at 900 °C, with a slight deactivation with time on stream. After 180 min of time on stream, the hydrogen yield was observed to be more or less same (49 ± 2%), at all of the temperatures. The iron catalyst exhibited quite high catalytic stability, where the hydrogen yield remained more or less same. The structural characterization of spent catalysts indicated the formation of metal encapsulated carbon nanoonions and few layered graphene sheets over Ni and Fe catalysts respectively. The crystallinity of the nanocarbon was found to be increasing with increasing the reaction temperature and a high graphitization degree was observed for the nanocarbon deposited at 900 °C, over both of the unsupported catalysts.