Production of hydrogen and carbon nanofibers by methane decomposition over the Ni/SiO₂ catalyst

Catalytic decomposition of methane is a promising route for hydrogen production owing to simple operation, easy separation of the products and no CO_x emission. In this work, a mesoporous Ni/SiO₂ catalyst was prepared by impregnation method and used in methane decomposition; the fresh and spent catalysts and the morphology of deposited carbon were characterized by N₂ adsorption-desorption, X-ray diffraction, hydrogen temperature programmed reduction, scanning electron microscopy and transmission electron microscopy. The effects of calcination temperature, metal loading and reaction temperature on the catalytic performance of Ni/SiO₂ in methane decomposition were investigated. The results show that the Ni/SiO₂ catalyst exhibits mesoporous structure. The calcination temperature has a slight effect on the textural properties and catalytic performances of Ni/SiO₂, but a significant influence on the agglomeration degree of Ni particles on the catalyst surface. The catalytic activity of Ni/SiO₂ increases first with increasing the metal loading up to 30% and then declines with a further increase of metal loading. Meanwhile, the reaction temperature has a remarkable influence on the catalytic activity and stability and the state of the deposited carbon; a high temperature results in the decrease of the catalytic stability and the formation of encapsulated carbon. In particular, for the methane decomposition over the 30% Ni/SiO₂ catalyst, the methane conversion of about 9.8% was obtained at 500 °C after reaction for 1000 min; the yield of carbon nanofiber at 500 °C is about 7.2 times higher than that at 650 °C.