Low-temperature oxidation of carbon monoxide with gold(III) ions supported on titanium oxide.

Au/TiO2 catalysts prepared by a deposition-precipitation process and used for CO oxidation without previous calcination exhibited high, largely temperature-independent conversions at low temperatures, with apparent activation energies of about zero. Thermal treatments, such as He at 623 K, changed the conversion-temperature characteristics to the well-known S-shape, with activation energies slightly below 30 kJ mol(-1). Sample characterization by XAFS and electron microscopy and a low-temperature IR study of CO adsorption and oxidation showed that CO can be oxidized by gas-phase O2 at 90 K already over the freeze-dried catalyst in the initial state that contained Au exclusively in the +3 oxidation state. CO conversion after activation in the feed at 303 K is due to Au(III)-containing sites at low temperatures, while Au(0) dominates conversion at higher temperatures. After thermal treatments, CO conversion in the whole investigated temperature range results from sites containing exclusively Au(0).

Spectroscopic investigation of the covalence of An(III) complexes with tetraethylcarboxamidopyridine.

In this work, we report a combined NMR spectroscopic and time-resolved laser fluorescence spectroscopic (TRLFS) study of the complexation of N,N,N',N'-tetraethyl-2,6-carboxamidopyridine (Et-Pic) with Ln(III) (La, Sm, Eu, and Lu), Y(III) and An(III) (Am and Cm). The focal point of this study was the metal-ligand interaction in the [M(Et-Pic)3]3+ (M = An and Ln) complexes. The NMR analyses found slight differences between the An(III)-N and Ln(III)-N interactions in contrast to the similar properties of the Am(III)-O and Ln(III)-O interactions. These results were supported by TRLFS which shows that the 1 : 3 Cm(III) complex is by one order of magnitude more stable than the respective Eu(III) complex. Thus, the ligand's selectivity lies in between those of pure N- and O-donor ligands. The selectivity results from a small partial covalent bonding between the An(III) ions and Et-Pic.

"Dirty nanostructures": aerosol-assisted synthesis of temperature stable mesoporous metal oxide semiconductor spheres comprising hierarchically assembled zinc oxide nanocrystals controlled via impurities.

Structural disintegration or the loss of accessible surfaces of functional nanostructures due to processes involving mass transport (e.g. sintering) is a serious problem for any application of these materials at elevated temperatures, like in heterogeneous catalysis or chemical sensing. Phases with low sintering temperatures, e.g. some metals or metal oxides like zinc oxide (ZnO), are very sensitive in this respect. Therefore, it is not only relevant to prepare important materials with refined morphologies, but the desired features need to be stable under real conditions. In this study, we describe the preparation of mesoporous ZnO nano-/microspheres by means of a template-assisted aerosol technique. Furthermore, by intentional introduction of impurity elements as dopants, specific surface areas and porosities of the prepared materials can be increased significantly. The impurities also strongly improve the thermal stability of the described ZnO nanostructures against thermal sintering. Although the pure ZnO material suffers from a complete loss of porosity, the structures of the impure ("dirty") materials change only negligibly. Even at 500 °C morphology and porosity are preserved. The latter advantageous property was used for testing the novel nanocatalysts in heterogeneous catalysis.