Templated synthesis for highly ordered metal/support nanocomposite materials with catalytic applications
Template synthesis is a powerful method of synthesizing materials with tunable properties. Tailorability of the templates makes it a viable method for high performance material synthesis. Surfactant, polymers and semiconductors have been used as templating tools for a long time. In the present work, we demonstrate the ability to synthesize hexagonally organized porous titania, zirconia and zirconia/titania mixed oxide supports and their respective nanocomposites of Pt from their alkoxide precursors using a highly viscous mixed surfactant template, separating nanoscopic bicontinuous channels of water and isooctane. Oil soluble precursor that eventually forms the support, precipitates at the oil-water interface mimicking the microstructure of the template. Subsequent reduction of Pt precursor in the aqueous nanochannels decorates the surface of the macropore walls with well-separated platinum (Pt) nanoparticles. This technique enables us to synthesize two components in a single template system by utilizing both oil and water phases. The composite formed possess a bimodal pore size distribution with one mean pore size ∼3.5nm (nanopores) and the other in the larger mean pore diameter regions ∼100nm-2μm (macropores), depending on the oxide support. Because of the decreased mass transfer resistance provided by the ordered and interconnected macropores in the support, the Pt/TiO2 nanocomposite exhibits a significantly higher carbon monoxide oxidation efficiency than that obtained with a commercial support that has a 4-fold larger specific surface area (at equivalent Pt loadings). We further demonstrate that simple changes in the post-synthesis processing can improve the properties of the material. Altering the drying technique and calcination temperature result in a substantial improvement in the specific surface area of the support material making them better than or comparable to the commercial support materials. We are able to synthesize materials with very low Pt loadings ∼0.05% (w/w). The nanocomposites are tested for CO oxidation and NOx reduction reactions. A comparison of the catalytic activity of Pt/ZrO2/TiO2 with Pt/TiO2 and Pt/ZrO2 showed that Pt/ZrO2 is most effect of the supports for NOx reduction reaction. This simple templated synthesis strategy for creating highly ordered composites has wide applications beyond the one reported here, including photocatalysis, photonic crystals, sensors and solar cells assemblies. ^
Engineering, Chemical|Engineering, Materials Science
"Templated synthesis for highly ordered metal/support nanocomposite materials with catalytic applications"
Dissertations and Master's Theses (Campus Access).