Investigation On Production Of Hydrogen And Carbon Nano-material From Methane Catalytic Decomposition

Methane catalytic decomposition (MCD) was carried out in the work to producehigh quality single-walled carbon nanotubes (SWCNTs). The Fe/Mg catalysts wereprepared via an improved co-precipitation method. We changed the mixing way ofmetal salts solution and precipitant to control the slurry pH and confirmed thestructure of the precursor with XRD and TG. A varied pH co-precipitation methodleads to a Feitknecht-compound (FC) containing precursor, and the oxides obtainedfrom which is proved to manifest a strong metal support interaction (MSI). The porestructure of the precursor rinsed with ethanol was improved and facilitates a largersurface area compared to water.We tested the different reaction condition and confirmed the optimum reductionand reaction temperature700and800oC, respectively. A high reduction temperature(>700oC) leads to aggregation of the reduced metal particles and a low reductiontemperature (<700oC) leads to too few active sites. The catalyst particles are easilyburied by carbon at a high reaction temperature and show a low activity at a lowreaction temperature. The activities of ethanol rinsed catalysts are higher than thewater rinsed ones. The HRTEM results indicate that the CNTs produced on thecatalyst with strong MSI are much cleaner and smoother, which is also confirmed bythe TG results. We analyzed the diameter distribution of SWCNTs, and found that thestrong MSI facilitates a narrow distribution, which was agreed with the Raman results.And the Raman spectra proved the graphitization degree was improved with a strongMSI.Ni/Fe/Al catalysts prepared with a co-precipitation method were used in MCD toproduce hydrogen and carbon nano-material. The XRD patterns indicated theprecursors had FC structure. We tested the activity of the catalysts with different Fecontents and investigated the effects of reaction temperature. The results showed thatthe addition of Fe to Ni/Al catalyst improves the activity. Fe/Ni alloy was formed andthe results of HRTEM proved that the morphology of metal particles changed frompolyhedron to qusi-liquid, which affected the stability of catalyst. The lifetime of2Ni-Fe-Al catalyst reached200h, and the carbon deposition was746.8and851.3g/g(Ni+Fe) at600and650oC, respectively. The results of HRTEM showed the solid carbon products were carbon nanofibers(CNFs) and multi-walled carbon nanotubes (MWCNTs). The EDS analysis of catalystparticles with different reaction time proved the reconstruction of catalyst proceeds allthe time. The TG results illustrate that the graphitization degree of solid carbon onNi/Fe/Al is lower than on Ni/Al, but the reconstructed Ni/Fe/Al catalyst were moresuitable to produce solid carbon with high graphitization degree.