Methane decomposition into COx free hydrogen and multiwalled carbon nanotubes over ceria, zirconia and lanthana supported nickel catalysts prepared via a facile solid state citrate fusion method

Abstract

Methane decomposition is the most effective route for the simultaneous production of COx-free hydrogen and nanocarbon. In this work, a set of porous ceria, zirconia and lanthana supported nickel catalysts were successfully synthesized via a facile solid state citrate fusion method and used for the thermocatalytic decomposition of undiluted methane for the first time. The catalysts were completely characterized for their crystalline, structural, textural and reduction properties and correlated to their catalytic performance. The active phase of fresh catalysts was found to be NiO in the CeO2 and ZrO2 supported catalysts whereas the formation of lanthanum nickel oxide solid solution was observed in the Ni/La2O3 catalyst. Various attractive porous morphologies of the fresh catalysts were confirmed by scanning electron microscopic studies. All of the catalysts exhibited high catalytic activity and stability for methane decomposition. The yield of hydrogen and carbon increased significantly with increasing the reaction temperature from 600°C to 700°C. A maximum initial hydrogen yield of 62%, 61% and 58% and a final carbon yield of 1360wt%, 1159wt% and 1576wt% was achieved over ceria, zirconia and lanthana supported catalysts respectively, at 700°C. The surface area of the catalysts could not have any significant effect on the catalytic efficiency and it was fully depended on the metal support interaction. The Ni/La2O3 catalyst showed high catalytic stability than ceria and zirconia supported catalysts due to the enhanced surface dispersion of finely crystallized Ni nanoparticles on the lanthana matrix aroused by the reduction of lanthanum nickel oxide. Moreover, bulk deposition of highly uniform multiwalled carbon nanotubes with high graphitization degree (ID/IG=0.95) with different diameters depending on the Ni crystalline size was observed over the catalysts.