Synthesis of carbon nanofibres over nanoporous Ni-MgO catalyst: influence of the bimetallic Ni-(Cu, Co, Mo) MgO catalysts

摘要

In this study, methane decomposition was conducted over monometallic Ni and bimetallic Ni-(Cu, Co, Mo) catalysts based on nanoporous MgO support to produce CO_x-free hydrogen and carbon nanofibres (CNFs). The MgO support was prepared by the sol-gel method and the catalysts were prepared by incipient wetness impregnation. The molar ratio of Ni to Mg was found to be around 0.76 and the molar ratios of transition metals Cu, Mo and Co to Ni were found to be around 0.23, 0.15 and 0.25, respectively. The methane decomposition reactions were performed at temperature of 570℃ over a nanoporous catalyst sample using the chemical vapour deposition technique in a fixed bed reactor. The X-ray diffraction pattern of the air-reduced catalysts confirmed the presence of metallic oxides as solid solution in the calcined samples. The maximal carbon and hydrogen yields, 3.62 g_C/g_(Ni) and 36.16 mol_(H_2)/mol_(Ni) were obtained with the Ni-MgO catalyst, respectively, during 1 h of reaction time. The Ni-Cu-MgO catalyst exhibited pronounced catalytic activity for several hours time-on-stream with accumulated carbon and hydrogen yields of 5.85 g_C/g_(Ni) and 58.39 mol_(H_2)/mol_(Ni), respectively, during 1 h of reaction time. However, adding Mo to the Ni-based catalyst increased the activity of the catalyst only by a slight increase (3.90 g_C/g_(Ni·1h)). Scanning and transmission electron microscope images of solid carbon showed hollow core herringbone structure of CNFs formed by a tip-growth mechanism.