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.</p

Investigation of Sm₂O₃–CeO₂-supported palladium catalysts for the reforming of methanol: The role of the support

With a view to their use as catalytic anode materials for direct methanol solid oxide fuel cells (DM-SOFCs), the performance of Pd/CeO2-SM2O3 (Pd/CS), Pd/CeO2 and Pd/SM2O3 catalysts in the steam reforming of methanol as well as their physicochemical properties - analyzed by N-2 adsorption, XRD, temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS) - have been investigated. The catalytic activity in methanol steam reforming was evaluated in a tubular microreactor at atmospheric pressure in the 300-500 degrees C reaction temperature interval (space velocity = 0.32 mol/(h g(cat)) H2O/CH3OH molar ratio = 1.2, methanol concentration 15 mole%). H-2, CO and CO2 were the main reaction products. Methanol conversions up to 72% and H-2 productivities as high as 0.46 mol/(h g(cat)) were obtained on the Pd/CS catalyst. Moreover, low H-2 productivity (0.09 mol/(h g(cat))) was found on the Pd/CeO2 catalyst, while Pd/Sm2O3 appeared to be inactive. This behaviour can be partly assigned to the higher dispersion and the more favourable distribution of Pd particles observed in the Pd/CS catalyst. A strong association of Pd and samarium oxide and an enrichment in both components at the external surface of the Pd/CS catalyst grains was found by means of TPR and XPS. This could be explained by the partial dissolution of Sm2O3 in the acid medium used during catalyst preparation leading to the re-precipitation of a Pd/Sm-containing phase. Higher activity per exposed Pd atom was also observed for the Pd/CS catalyst. This was attributed to enhancement of diffusion and adsorption of reactants on the basic sites of the Sm-containing support. (c) 2005 Elsevier B.V. All rights reserved.</p

Investigation of Sm₂O₃–CeO₂-supported palladium catalysts for the reforming of methanol: The role of the support

With a view to their use as catalytic anode materials for direct methanol solid oxide fuel cells (DM-SOFCs), the performance of Pd/CeO2-SM2O3 (Pd/CS), Pd/CeO2 and Pd/SM2O3 catalysts in the steam reforming of methanol as well as their physicochemical properties - analyzed by N-2 adsorption, XRD, temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS) - have been investigated. The catalytic activity in methanol steam reforming was evaluated in a tubular microreactor at atmospheric pressure in the 300-500 degrees C reaction temperature interval (space velocity = 0.32 mol/(h g(cat)) H2O/CH3OH molar ratio = 1.2, methanol concentration 15 mole%). H-2, CO and CO2 were the main reaction products. Methanol conversions up to 72% and H-2 productivities as high as 0.46 mol/(h g(cat)) were obtained on the Pd/CS catalyst. Moreover, low H-2 productivity (0.09 mol/(h g(cat))) was found on the Pd/CeO2 catalyst, while Pd/Sm2O3 appeared to be inactive. This behaviour can be partly assigned to the higher dispersion and the more favourable distribution of Pd particles observed in the Pd/CS catalyst. A strong association of Pd and samarium oxide and an enrichment in both components at the external surface of the Pd/CS catalyst grains was found by means of TPR and XPS. This could be explained by the partial dissolution of Sm2O3 in the acid medium used during catalyst preparation leading to the re-precipitation of a Pd/Sm-containing phase. Higher activity per exposed Pd atom was also observed for the Pd/CS catalyst. This was attributed to enhancement of diffusion and adsorption of reactants on the basic sites of the Sm-containing support. (c) 2005 Elsevier B.V. All rights reserved.</p

Disposal of CCl4 by disproportionation reaction with CH4

A method for disposal of ozone-depleting CCI4 by disproportionation reaction with CH4 to produce CH3Cl and CHCl3 has been investigated over various platinum-based catalysts. The catalysts were supported mainly on SiO2 and MgO and also modified by the addition of manganese to improve the catalyst lifetime. Platinumbased catalysts supported on SiO2, MgO, and MgAl2O4 showed stable activity and high selectivity to CH3CI at 730 K during the reaction time of 40 h. However, large amounts of carbon deposition as well as transformation of the supports to chlorinated forms were observed and resulted in catalyst deactivation during operation for longer periods. The catalysts modified with manganese have shown an enhancement of catalytic stability and selectivity to CH3CI. Furthermore, addition of a moderate amount of molecular oxygen (mole ratio Of O-2/CCl4 > 0.6) during the reaction over Mn-modified catalysts resulted in the efficient removal of deposited carbon and also the enhancement of selectivity to CH3CI-close3