Pretreatment-Induced Nanostructural Evolution in CeO2-, Sm2O3-, and CeO2/Sm2O3-Supported Pd Catalysts for Intermediate-Temperature Methanol Fuel Cells

Catalysts of 2 wt % Pd supported on CeO2, Sm2O3, and CeO2/Sm2O3 (in a 4:1 molar ratio) were studied in detail by high-resolution transmission electron microscopy and elemental mapping, both as-prepared and after undergoing one of three reduction pretreatments of increasing severity. The evolution in the nanostructure, composition, and disposition of the phases were studied in detail as a function of starting composition and of pretreatment conditions. The trends observed were compared with the trends in activity and selectivity of the catalysts for hydrogen generation front methanol fuel, with a view to their application in direct methanol intermediate-temperature solid oxide fuel cells. The catalyst preparation conditions had a dramatic effect on the Sm-containing materials but not on the Pd/CeO2. The Pd/CeO2/Sm2O3 catalyst was seen to develop a beneficial hierarchical structure in which Pd particles were supported on fine Sm2O3 crystallites, which were ill turn supported on larger CeO2 particles. This effect may be useful for the deliberate design of such nanostructured catalysts.