Cu/Co/Ce Composite Oxides Supported On Multi-walled Carbon Nanotubes For Catalytic Removal Of Co In A H₂-rich Stream

The hydrogen production is one of the crucial technologies for the future hydrogen energy economy and the polymer electrolyte membrane fuel cell (PEMFC) is regarded as one of the most promising environment-friendly fuel cell technologies owing to its high energy efficiency. The fuel processing of hydrocarbons as the most common hydrogen production method in commercial use, mainly consisting of the reforming and water gas shift reactions, may also produce some amounts of CO. However, the remaining CO can easily poison the Pt-based anode of PEMFC and thus should be removed to a trace level. In contrast to the physical methods such as cryogenic separation, pressure swing adsorption and selective diffusion of H2, the developing approaches by catalytic removal of CO in a H2-rich stream mainly involve the preferential oxidation (PROX) of CO and the selective CO methanation. Cu-Ce mixed oxides catalysts have attracted much attention because of their low cost and high selectivity PROX reaction. Many efforts have been made to promote the activity of CuO-CeO2catalysts by employing various preparation methods, doping with other metals and using different support materials.In the present study, multi-walled carbon nanotubes (MWCNT) supported CUO-CO3O4, CeO2-Co3O4and Co3O4-CuO-CeO2mixed oxides catalysts were prepared using an impregnation method aided by ultrasonication treatment. The structure properties of the catalysts were characterized by XRD, TEM, H2-TPR, XPS and Raman spectra. The catalytic performance of CO removal in a H2-rich stream was examined in detail.For CuO-CO3O4system, the structure properties of the catalysts indicate the strong interactions between Cu and Co mixed oxides as well as between metal oxides and MWCNT support. In contrast to the single Cu and Co catalyst, the unique performance was observed for Cu-Co composite catalysts, which features an unusual reaction pathway through the combination of CO preferential oxidation and CO methanation especially at high reaction temperature. The optimal catalyst with Cu/Co ratio of1/8can achieve the complete CO conversion in a wider temperature range of150-250℃under the space velocity as high as120,000ml h-1g-1, which proves a promising catalyst for the effective CO removal in a H2-rich stream. For CeO-Co3O4system, the main active component is cobalt oxides, while the proper amount of Ce doping can improve the catalytic activity. With respect to the Co3O4-CuO-CeO2system, the formation of ternary mixed oxides cannot enhance the catalytic activity, and the decline in activity increases with the amount of dopant such as Co and Zn to the CuO-CeO2catalyst.