(45b) Tailoring the Pore Morphology of Pure and Mixed La- and Ce-Oxides

Advances in materials chemistry over the past decade have opened new possibilities for tailoring the properties of technical catalysts from the nanoscale up. Nanoporous materials, with well-defined pore morphologies, i.e. controlled pore diameter and structure, give rise to large and highly accessible internal surface areas, as well as unique properties such as molecular sieving capabilities and/or the capability to integrate multiple functionalities into a single material.

We are reporting on the synthesis, characterization, and testing of nanostructured CeO2- and La2O3-based catalysts for the Water-Gas Shift (WGS) reaction. The work builds onto our previous work in which we demonstrated the unusual stability of noble metal/alumina nanocomposite materials in high-temperature catalysis, such as catalytic partial oxidation of methane to synthesis gas. Target of the present work is the synthesis of similar nanocomposites by embedding metal nanoparticles into a nanostructured CeO2 and/or La2O3 matrix. Both oxides have previously been shown to be effective (and active) support materials for noble metal-based catalysts in WGS. However, previous work has mostly focused on the effect of ?nano-sizing? the active metal component in these catalysts, although recent evidence indicates that the structure of the oxide support is much more important than given credit to-date.

Our synthesis is based on a reverse microemulsion-templated sol-gel synthesis, in which the embedded metal nanoparticles are synthesized simultaneously with the ceramic matrix. This templating route allows for a flexible tailoring of the catalyst morphology by manipulation of a variety of synthesis parameters. In this way we have successfully synthesized a range of pure and mixed CeO2- and La2O3-based nanostructured ceramic supports with high surface area and good thermal stability over a broad temperature range of relevance for WGS. The resulting materials were characterized via SEM, TEM, XRD, BET, and chemisorption. We found that the pore size and surface area of pure CeO2 or La2O3 materials can be tailored via synthesis parameters such as the water:alkoxide ratio. The synthesis of mixed CeO3-La2O3 provides not only higher surface area than either of the pure oxides over the relevant temperature range, but the Ce:La ratio also has a profound impact on the pore morphology of these resulting materials.

Finally, Au, Ni, and Pt nanoparticles were successfully embedded into these nanostructured ceramic supports with different pore morphologies. We are currently evaluating the activity and stability of these nanostructured catalysts in WGS. First results indicate excellent stability of these nanocomposite catalysts. Synthesis, characterization, and reactive tests will be discussed in detail in the presentation.