| The hydrogen production is one of the crucial technologies for the future energy economy with an increasing demand for the environment-friendly and clean energy systems, among which the polymer electrolyte membrane fuel cell (PEMFC) is considered one of the most promising fuel cell technologies due to its high energy efficiency and low operating temperature. As the most common hydrogen production method in commercial use, the fuel processing of hydrocarbons mainly consisting of the reforming and water gas shift reactions may produce an appreciable amount of carbon monoxide as well. However, the residual CO in a Hb-rich stream can poison the Pt-based anode of PEMFC and thus should be removed to a trace level. Among the various methods, the preferential oxidation (PROX) of CO is widely investigated as one of the primarily developing approaches by catalytic removal of CO in the H2-rich stream. A variety of catalysts was used in the CO-PROX, including supported noble metals (Pt, Ru and Rh), Au catalysts and metal oxides such as CuO-CeO2 catalysts. Among the reported catalysts, the Pt-based catalysts are regarded as the most promising candidates for PROX process, but the activities of Pt catalysts seriously suffer from the strong poisonous adsorption by CO substrate at low reaction temperature. Many efforts have been made to promote the PROX activity of Pt-based catalysts by doping or incorporating with other transition metals or change different carrier. Compared with the precious metal catalyst system, Cu-Ce mixed oxides catalysts have attracted much attention because of their low cost and high selectivity PROX reaction.In the present study, the functionalized multi-walled carbon nanotubes (MWCNT) were used as the support to prepare the Pt-Fe and Cu-Ce double metal/oxides composite catalysts by an impregnation method aided by ultrasonication treatment. After a series of characteration of the catalyst, we also used the CO oxidation reaction device to test the activity and selectivity of catalysts and associated the characterization data with the performance of the catalyst.For Pt-Fe(r)/CNTs system, the structure properties of the catalysts indicate the fine dispersion of Pt-Fe species on MWCNT by the partial formation of Pt-Fe solid solution or alloy with the dominated metallic Pt phase. The Pt-Fe species may preferentially attach to the defects of the MWCNT support, which can greatly modify the redox properties of Pt-Fe/CNT catalysts, suggesting the strong interactions between Pt and Fe as well as between metal nanoparticles and MWCNT support. Remarkable catalytic performance in CO-PROX reaction can be identified over the Pt-Fe/CNT catalysts in comparison with those supported on other materials. The optimal activity is achieved for the catalyst with a Pt/Fe ratio of 4/0.8, keeping complete CO removal and fair CO2 selectivity in the temperature range of 40-200 ℃ under a space velocity as high as 120,000 ml h-1 g-1. For CuO-CeO2/VCNTs system, the influence of support properties and preparation methods was investigated. Series catalysts were prepared on MWCNT supports with or without calcination at 800℃ by different steps of impregnation. The catalytic performance of CO-PROX indicated that the best reactivity can be observed for CuO-CeO2 mixed oxides supported on MWCNT without further calcination by a co-impregnation metod, which may be ascribed to the formation of more active Cu-Ce interface due to the co-impregnation of Cu and Ce and the presence of more surface functional groups on MWCNT support without further calcination. |
PDF Full Text Request