One-pot sol-gel synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon

Abstract A single pot sol-gel method was adopted for the synthesis of MgO nanoparticles supported nickel and iron catalysts for undiluted methane decomposition into COx free hydrogen and nanocarbon for the first time. The catalysts were successfully synthesized via a facile sol-gel route without the assistance of any surfactants. The as-synthesized catalysts were completely characterized for their structural, textural and redox properties using several analytical techniques. The X-Ray diffraction analysis confirmed the formation of NiMgO solid solution and magnesioferrites as the active phases in the fresh catalysts. The inter-aggregation of nanoparticles in the catalyst generated pores, and a mesoporous texture resulted. The hydrogen chemisorption analysis indicated that the NiMgO solid solution was very difficult to reduce compared to the magnesioferrites. The thermocatalytic decomposition of methane at 700 °C, 800 °C and 900 °C fully validated their enhanced catalytic activity and stability for the reaction. The initial hydrogen yield and total carbon yield were found to be significantly increased, when the reaction temperature was increased. However, the highest catalytic performance was shown by the Fe/MgO catalyst. Moreover, no catalyst deactivation was observed for both of the catalysts for a period of 360 min of time on stream. This could be ascribed to their enhanced catalytic stability due to the presence of metal nanoparticles dispersed on the surface of the support, with proper metal-support interaction rather than their specific surface area. Multiwalled carbon nanotubes with metal encapsulated carbon particles and few layered graphene sheets were deposited over Ni/MgO and Fe/MgO catalysts, respectively. The studies of the effect of reaction temperature on the crystalline properties of the deposited nanocarbon indicated that the crystallinity and graphitization degree were increased with increasing reaction temperatures.