| Summary: | 博士 === 國立清華大學 === 化學系 === 94 === Alloy catalyst of 10 wt% Pt50Ru50/C (with a Pt:Ru atomic ratio of 50:50) was prepared by methods of incipient wetness impregnation and co-precipitation and then activated by hydrogen reduction. TEM and XRD examinations indicated that bimetallic crystallites were finely dispersed with a diameter of dPtRu ~ 2 nm on the reduced catalyst. TPR characterization suggested that deposited bimetallic crystallites exhibited a cherry-like structure with Pt at shell and Ru in core. Catalytic activity of the prepared catalyst toward electro-oxidation of methanol was examined by cyclic voltammetry (CV). The activity of alloy catalyst was found promoted by two kinds of modifications, incorporation of ceria and oxidation treatment.
The promotion of ceria was attributed to an increase in the dispersion of deposited alloy crystallites. However, the extent of promotion depended heavily on the procedure of catalyst preparation and the loading of ceria. Evidently, portion of the alloy particles did not participate in reaction due to being impregnated into internal pores of carbon support as well as occluded into bulk of CeO2 crystallites codeposited. A promoted catalyst with the highest exposure of Pt-Ru nanoalloys exhibited the best electro-activity to methanol oxidation.
The size and the structure of dispersed crystallites were found changed on increasing the temperature of oxidation treatment (To). On mild oxidation, atoms of Ru in the core were found gradually segregated to the surface of bimetallic crystallites and oxidized to amorphous RuO2. Crystalline RuO2 (RucO2) was formed on extensive segregation at To > 520 K. The promotion of oxidation treatment was therefore attributed to the segregation of Ru and the formation of RucO2. Oxidation treatment at elevated temperatures of To > 600 K, however, caused a deactivation to the electro-activity. The deactivation is interpreted with excessive oxidation of the carbon support and a severe sintering of dispersed crystallites.
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