الفهرس 
INTRODUCTION AND LITERATURE SURVEYOnly 14 pages are availabe for public view
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Abstract
Graphene nanosheets (GNSs) and pure hydrogen gas have been successfully produced by catalytic deposition of methane (CDM) using different unsupported bimetallic catalysts. Firstly, Fe-Mo, Co-Mo and Ni-Mo were prepared by liquid fusion method and tested for CDM. According to the XRD, H2-TPR and FT-IR results of the fresh catalysts, the metal molybdates species were the predominant components of the Mo-Me catalysts. On the other hand, XRD, TEM and Raman spectra results of spent Mo-Me catalysts revealed the deposition of graphene sheets with high-quality and graphitization degree on their surfaces. The catalytic activities of the Mo-Me catalysts in terms of H2 and graphene yields were as follows: Mo-Fe > Mo-Co > Mo-Ni. The optimum H2 yield values were ̴ 62, 25 and 17% using Mo-Fe, Mo-Co and Mo-Ni catalysts, respectively. Moreover, the graphene yield values were 59, 43 and 11%, respectively. The high activity of Mo-Fe and Mo-Co catalysts is due to the high stability of iron and cobalt molybdates species exist in the catalysts. In this context, the partial segregation of the NiMo carbide phase into the inactive Mo2C and the active Ni3C species was the main reason for the low activity of the Mo-Ni catalyst. Finally, the catalytic activity results showed that all Mo-Me catalysts can operate for extended periods before being deactivated, suggesting that they could be promising catalysts in the current reaction.
Based on the previous results, a series of catalysts including, 100%Fe, 100%Mo and bimetallic Fe-Mo catalysts with different Fe/Mo ratios were prepared and evaluated for GNSs and H2 production via the CVD of methane at 800 °C. The XRD and TPR data of the fresh catalysts revealed that non-interacted Fe2O3 and FeMoOx particles were predominant in the catalysts with greater Fe concentrations. In contrast, the excess incorporation of Mo into the Fe catalyst leads to the formation of inactive Mo2C species. The resulting data showed that the morphology and microstructure of GNSs are strongly influenced by the variation of Fe/Mo ratios. The change in Fe/Mo ratio was shown to have a critical role in the catalytic growth activity and stability, as well as the shape and microstructure of as-grown GNSs. Among all examined catalysts, the 50%Fe-50%Mo catalyst was the most active for the production of GNSs and H2. Conversely, the 100%Mo catalyst was inactive for the decomposition reaction.
Finally, a series of Fe-Mo-MgO catalysts with various Mo/Mg ratios (0/50, 10/40, 20/30, 30/20, 40/10 and 50/0) were prepared and tested for the production of CNTs/GNSs hybrid materials and hydrogen gas via the CVD of methane. It was demonstrated that the Mo/MgO ratio significantly affects the performance of the Fe-Mo-Mg catalysts and the type of carbon deposited. According to TEM observations, CNTs and GNSs were formed on the surface of binary Fe-Mg and Fe-Mo catalysts, respectively. The existence of highly dispersed Fe nanoparticles in the MgFeOx species resulted in the individual growth of CNTs on the Fe-Mg catalyst. On the other hand, the highly aggregated FeMoOx particles were found to be responsible for the growth of GNSs on the surface of Fe-Mo catalyst. The gradual addition of Mg from 10% to 30% to the Fe-Mo catalyst enhanced the dual growth of CNTs and GNSs hybrid structures. Raman spectra showed that the as-deposited CNMs on all Fe-Mo-Mg catalysts had high crystallinity and graphitization level regardless of their nature or morphology. Furthermore, the yields of H2 and CNMs were shown to rise with increasing MgO contents in the catalyst composition due to the successive formation of active MgFeOx species.