Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum

International audience; Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria ``nanopocket'', which binds Pt2+ so strongly…

Reversible oxidation of WOx and MoOx nano phases

International audience; WOx and MoOx nano phases were prepared on TiO2(1 1 0) surfaces by a CVD procedure consisting of adsorption and decomposition of W(CO)(6) or Mo(CO)(6) precursors followed by annealing under UHV. Metal amount involved in each elaborated sample is in the fractional range from 0.1 to 0.35 equivalent monolayer (eqML) of W or Mo. Evolution of sample stoichiometry as a function of subsequent treatment is followed by valence band and core level photoemission as well as work function measurement. In each case, exposure of samples to molecular oxygen at room temperature induces an increase of sample work function in a range of several tenth of eV. Such a work function change i…

Evidence of hexagonal WO3 structure stabilization on mica substrate

International audience; WO3 nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO3 hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO3 hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.

Back Cover: Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum (Angew. Chem. Int. Ed. 39/2014)

An epitaxial hexagonal tungsten bronze as precursor for WO3 nanorods on mica.

International audience; Tungsten oxide nanorods are grown at atmospheric pressure and low temperature (360 1C), by sublimation of WO3 and condensation on mica substrates. The nanorods are characterized by atomic force microscopy, high-resolution electron microscopy, energy-dispersive X-ray spectroscopy and high energy electron diffraction. The experimental results evidence the formation of a hexagonal tungsten bronze at the nanorod–substrate interface. The epitaxial relationships of the nanorods on mica are determined and the role of epitaxial orientation of the interfacial bronze in the nanorod growth and morphology are discussed.

TiO2 anatase films obtained by direct liquid injection atomic layer deposition at low temperature

International audience; TiO2 thin films were grown by direct liquid injection atomic layer deposition (DLI-ALD) with infrared rapid thermal heating using titanium tetraisopropoxide and water as precursors. This titanium tetraisopropoxide/water process exhibited a growth rate of 0.018 nm/cycle in a self-limited ALD growth mode at 280 degrees C. Scanning electron microscopy and atomic force microscopy analyses have shown a smooth surface with a low roughness. XPS results demonstrated that the films were pure and close to the TiO2 stoichiometric composition in depth. Raman spectroscopy revealed that the films were crystallized to the anatase structure in the as-deposited state at low temperatu…

Rücktitelbild: Auf dem Weg zu größtmöglicher Effizienz bei der katalytischen Nutzung von Edelmetallen: atomar dispergiertes Oberflächen-Platin (Angew. Chem. 39/2014)

Growth, Structure, and Stability of KxWO3 Nanorods on Mica Substrate

International audience; KxWO3 nanorods, interesting as gas sensors, were elaborated on mica muscovite substrate and characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and mainly transmission electron microscopy. A combination of structural analyses allowed determining the morphology of these rods, and selected area electron diffraction experiments pointed out the simultaneous presence of the exotic hexagonal and stable monoclinic phases. Moreover, the presence of potassium inside the nanorods, coming from the mica substrate, was revealed. By combining all the observations, a growth model is proposed, consisting of the stacking of two di…

Deposition of Pt and Sn doped CeOx layers on silicon substrate

Abstract Radio Frequency Magnetron Sputtering is used to elaborate CeO x layers doped with platinum and/or tin on a SiO 2 /Si substrate. Morphology, chemical composition and crystallographic structures were investigated by Transmission Electron Microscopy. The presence of nanoparticles of mainly ceria and metallic platinum is exhibited.

WOx phase growth on SiO2/Si by decomposition of tungsten hexacarbonyl:Influence of potassium on supported tungsten oxide phases

International audience; Synchrotron based photoemission spectroscopy was used to study the adsorption of tungsten hexacarbonyl on SiO2 surfaces modified by potassium. Results were compared with the ones obtained when no potassium was present. Experiments using W4f and Si2p intensities variations show that, at 140 K, the tungsten hexacarbonyl growth proceeds via a simultaneous multilayer mode for the two kinds of surfaces but with differences in compositions of growing layers. Indeed, it is evidenced that, even at cryogenic temperatures, the presence of potassium induces decomposition of a significant part of tungsten hexacarbonyl molecules through a strong interaction between tungsten and p…

Auf dem Weg zu größtmöglicher Effizienz bei der katalytischen Nutzung von Edelmetallen: atomar dispergiertes Oberflächen-Platin

Platin ist das am vielseitigsten eingesetzte Element in der Katalyse. Allerdings begrenzt der hohe Preis des Edelmetalls die Verwendung in vielen Bereichen, z. B. in Katalysatormaterialien fur Brennstoffzellen. Trotzdem nutzen konventionelle Katalysatoren oftmals nur einen Bruchteil ihres Pt-Gehaltes, namlich diejenigen Atome, die sich auf der Oberflache des Katalysators befinden. Eine effizientere Edelmetallnutzung setzt somit eine hohere, bevorzugt atomare Dispersion der Pt-Atome auf der Oberflache voraus. Tatsachlich ist es moglich, solche atomar dispergierten Pt-Spezies mit sehr hoher Stabilitat auf einer Katalysatoroberflache herzustellen. Mithilfe von DFT-Rechnungen identifizieren wir…