| In recent years, polymer electrolyte membrane fuel cell (PEMFC) which utilizes hydrogen as a fuel has been attracting much attentions in the application to electric vehicles or residential power-generations due to its low operation temperature, excellent energy efficiency and zero-emission of air pollutants. Hydrogen for PEMFC is generally generated from steam reforming or partial oxidation of hydrocarbons or methanol followed by the water-gas shift reaction. However, typical hydrogen mixtures from such a process usually contain0.5-2%CO which can poison the Pt electrode in the PEMFC. Thus, carbon monoxide needs be decreased to a trace-level (below10ppm) to avoid poisoning of the Pt electrode. Among the current available methods to remove CO in the H2-rich gases, preferential oxidation of CO in H2-rich gases (PROX), was proved to be the most straightforward and economic one. So far, extensive studies have focused on improving the activity of the catalysts for CO-PROX reaction. However, developing efficient catalysts for PROX system is still a challenge.In this paper, the effect of preparation method and preparation factors of CeO2-MnOX on its texture properties and the effect of support texture properties on catalytic properties of Cu-based catalysts was investigated for CO PROX system. Physical and chemical properties, structure of CeO2-MnOX supports and CuO/CeO2MnOX catalysts were characterized by means of XRD, BET, EDS, XPS, N2-adsorption, TPR and TPD.1. CeO2, MnOX, CO3O4and ZnO were used as supports of Cu-based catalysts respectively in this study. The influences of these supports on the catalyst for CO oxidation in H2-rich gases were investigated. The results indicate that CuO/CeO2and CUO/CO3O4catalysts have higher catalytic activity for CO PROX system than CuO/MnOx or CuO/ZnO catalyst. The high CO conversion of CUO/CO3O4catalyst should be attributed to CO3O4as catalyst contributing to CO oxidation by itself. The CO conversion of CuO/CeO2catalyst at413K and433K are85%and97%, respectively. Comparing with the other two catalysts, CuO/CeO2catalyst has larger surface area, pore volume, CO adsorption amount and reduction peak area, while lower CO desorption and reduction temperature. Besides, there is a stronger metal-support interaction in CuO/CeO2catalyst than in other catalysts. All these favour the activity of the catalyst.2. The influences of MOX (M=Co, Mn, Al or La) on CuO/CeO2catalyst for CO oxidation in H2-rich gases were investigated. The results indicate that the addition of MnOX and CO3O4can improve the activity of CuO/CeO2catalyst for CO oxidation in H2-rich gases.The activity of CuO/CeO2-MnOX catalyst are the best among the CuO/CeO2-MOX catalysts, the CO conversion of CuO/CeO2-MnOX catalyst are58%and100%at80℃and140℃, respectively. Comparing with other samples, CuO/CeO2-MnOx catalyst has smaller crystal size, larger reduction peak area and CO adsorption amount, more copper and lattice oxygen species on the surface, temperature of CO desorption and CuO reduction is lower, interaction of metal oxides-support is stronger. All these are advantageous to the catalyst active enhancement.3. The effect of CeO2-MnOX calcination temperature on CO preferential oxidation in H2-rich gases over CuO based catalysts was investigated. Results show that calcination temperature of CeO2-MnOX supports have a direct effect on the structural properties, redox properties, catalytical activities of CuO/CeO2-MnOX catalysts for the CO preferential oxidation in H2-rich gases. CuO/CeO2-MnOX catalyst with CeO2-MnOX calcined at500℃exhibits higher CO conversion in H2-rich gas than the others. Partly formation of CeO2-MnOX solid solution, stronger interaction between the CeO2and MnOX, more amounts of highly dispersed CuXO, and more CO adsorption amounts should be related to its excellent catalytic performance.4. CeO2-MnOX with a Mn/Ce+Mn molar retios of0.1-0.9were prepared by coprecipitation method, and as supports of CuO/CeO2-MnOX catalysts.The effect of Mn/Ce+Mn molar retios in CeO2-MnOx on CO preferential oxidation in Hb-rich gases over CuO based catalysts was investigated. The effect of MnOX on the mobility of oxygen species in ceria of catalysts was especially surveyed, and a mechanism of oxygen species transfer on CuO/CeO2-MnOX catalyst was also proposed. The CuO/CeO2-MnOX with Mn/Ce+Mn molar ratios of0.3exhibited the highest catalytic activity among the CuO/CeO2-MnOX catalysts.5. Effect of CeO2-MnOX preparation methods on CuO catalyst for the preferential oxidation of CO in H2-rich gases has been investigated. The CeO2-MnOX supports have been prepared by deposition-precipitation, surfactant-templated, and solution mixed methods respectively. The characterization shows that surfactant-templated method may form CeO2-MnOX solid solution to increase the surface oxygen vacancies and surface area. Results of activity test show that the catalyst with CeO2-MnOX support prepared by surfactant-templated method exhibits the highest catalytic activity (CO conversion,100%at120℃). This could be ascribed to the larger surface area, stronger interaction between the CeO2and MnOx, larger amounts of highly dispersed CuXO and isolated copper ions.6. The CeO2-MnOX supports have been prepared by coprecipitation and modified coprecipitation. There are main Mn4+species in the support prepared by modified coprecipitation, whereas Mn3+is the main species in the support prepared by coprecipitation. Effect of Mn valence in CeO2-MnOX supports on Cu-based catalysts for the preferential oxidation of CO in H2-rich gases has been investigated. Though the two catalysts have similar structure, the catalyst with Mn4+species in the support has richer lattice oxygen on the surface and is easier reduction than that with Mn3+species. All these result in much higher catalytic activity.
|
PDF Full Text Request