الفهرس 
Natural GasOnly 14 pages are availabe for public view
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Abstract
Methane catalytic decomposition reaction into COx-free hydrogen and carbon nano-structured materials was conducted over three groups of ZrO2 supported catalysts. The first group consists of ZrO2-MgO supported cobalt catalysts with various Zr/Mg atomic ratios. At the optimum Zr/Mg ratio, the MgO was replaced by various oxides including Al2O3, SiO2, CeO2 and La2O3 in order to investigate their influence on the catalytic activity of the active cobalt site. Finally, the cobalt metal was compared with the nickel and iron supported on ZrO-MgO binary oxides as the most active support. All catalysts were prepared by the conventional impregnation method. The activity tests of the prepared catalysts were performed in a continuous fixed bed horizontal flow reactor at 700 oC under atmospheric pressure. The fresh and spent catalysts were characterized by XRD, TPR, BET, TEM and Raman spectroscopy.
The results showed that the change in Zr/Mg ratio of the mixed oxide support has a significant effect on the catalytic performance of the active Co metal. The catalyst 30%Co/Zr0.8Mg0.2 showed the highest activity and stability within the used series of catalysts with hydrogen yield reached up to 79%. Both Co/Mg1.0 and Co/Zr1.0 showed poor stability due strong Co-Mg interaction and aggregation of Co species on Zr support, respectively. On the other hand, the Co/Zr-Mg exhibited better activity in terms of hydrogen yield compared with the other Zr-Al, Zr-Si, Zr-Ce and Zr-La supported cobalt catalysts. This can be ascribed to the moderate cobalt oxide-support interaction and forming CoMgOx species which enhance the Co3O4 dispersion and prevent its aggregation on the catalyst surface. In contrast, the Co/Zr-Si catalyst showed the lowest activity due to the agglomeration of Co3O4 on the surface of the SiO2 support. In addition, the 30%Co/Zr-Mg catalyst exhibited higher catalytic decomposition activity compared to both 30%Fe/Zr-Mg and 30%Ni/Zr-Mg catalysts. TEM images showed that all cobalt-based catalysts produced mainly MWCNTs with different diameters and structures depending on the nature of the support type.
Keywords: Hydrogen production; methane decomposition, cobalt-based catalysts; zirconia support; multi-walled carbon nanotubes.