New Selective CO Methanation Catalyst For The Purilfcation Of Hydrogen-rich Gas Mixtures

Selective CO methanation has been considered to be a promising strategy in thethorough removal of CO from H2-rich gases for fuel cell, because it is easy to operate, and theproduct is safe to the Pt anodes of the PEMFC. Additionally, many other reaction processesdevelopment such as the competitive hydrogenation reaction and the temperature-sensitivereaction can be benefit greatly from the research of selective CO methanation.The Ru-Zr/CNTs catalyst was prepared by using Ru, carbon nanotubes （CNTs） and Zr asactive component, support and promoter, respectively, based on the theory analysis andexperimental results. It was found that the catalyst reduced at350℃presented excellentcatalytic activity, decreasing CO concentration to below10ppm from10000ppm by COselective methanation at the temperature range of180-240℃. Characterizations includingXRD, XPS, TEM and H2-TPR indicate that the Zr modification of Ru/CNTs results in theweakening of the the interaction between Ru and CNTs and a higher Ru dispersion.Additionally, the oxidized charge transfer to surface Ru became more easily, due to theexisitance of ZrO₂, which is benefit to CO activation on catalyst surface. No significantinfluences on the dispersion, structure and morphology of Ru-Zr/CNTs catalyst were found bychanging the CNTs features such as wall number, out diameter （OD） and the degree ofgraphitization.The CNTs-Ni foam was configurated by chemical vapor deposition （CVD）, in which themethane was employed as carbon source. It was found that the prepared active Ni particleswere well diapersed on the SiO₂coating by indirect impregnation method, leading to thefabrication of CNTs-Ni foam composite with narrow diameter distribution of CNTs at650℃.However, the diameter distribution of CNTs broadened with increasing reaction temperatureand Ni loading, due to the agglomeration and cracking of Ni particles. No significantdifferences in the CNT diameters were observed by changing weight hourly space velocity（WHSV）. Some CNTs are formed via tip-mechanism, while the other formed viabottom-mechanism. Raman analysis indicates that the as-formed CNTs are multi-wall CNTs（MCNTs）.The new Ru-Zr/CNTs-Ni foam composite catalyst was synthesized by using CNTs-Nifoam composite as support. In this catalyst, the CNTs is employed to disperse the activecomponent in nanometer size, assuring a high catalytic activity, while the Ni foam skeletonoffers high thermal conductivity and micro-channels in the size of micrometer order, allowingfor rapid heat transfer and minimizing the possibility of localized hot spots caused by the high exothermic reactions. The performance test shows that Ru-Zr/CNTs-Ni foam compositecatalyst has excellent catalytic performance, decreasing CO concentration to below10ppm byselective CO methanation at the temperature range of200-300℃, and keeping the COselectivity higher than60%. Compared with the results of Ru-Zr/CNTs, the Ru-Zr/CNTs-Nifoam composite catalyst has a wider temperature window where the CO level is less than10ppm and higher CO selectivity. The methanation of CO occurs over Ru-Zr/CNTs-Ni foamcomposite catalyst via two distinct pathways including dissociative reaction pathway andassociative reaction pathway. The first one dominates at low reaction temperature （<220℃）,while the second one dominates at high reaction temperature.