Decomposition of methane over Ni-SiO2 and Ni-Cu-SiO2 catalysts: Effect of catalyst preparation method Original Research Article

Ni catalysts supported on silica as textural promoter prepared by different methods are studied as catalysts for the thermo catalytic decomposition (TCD) of methane to produce hydrogen and deposited carbon in a fixed-bed reactor at 700 °C. The characterization of the fresh and used catalysts and the deposited carbon has been carried out by using different techniques like powder X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The effect of copper addition and the type of copper precursor used (nitrate or oxide) on Ni activity as the catalyst of the TCD process has also been investigated. Whatever the preparation method used, all catalysts showed a high and almost constant methane conversion without apparent deactivation after 8 h on stream, revealing the good catalyst performance in the TCD process. Copper as a nickel dopant increases the hydrogen production leading to hydrogen concentrations over 80 vol% in the production gas, independent of the preparation method or the copper precursor used. All catalysts studied promote the formation of carbon nanofibers some micrometers long with different diameters, especially dependent on the presence or absence of copper. Ni-Si catalysts prepared by the fusion method promote the formation of small carbon fibers with a rather narrow diameter distribution, while Ni-Cu-Si catalysts lead to the formation of larger fibers with a broad diameter distribution.