Search results for "Surfaces"
showing 10 items of 2837 documents
A Combined Theoretical and Experimental Approach for Platinum Catalyzed 1,2-Propanediol Aqueous Phase Reforming
2017
Decomposition pathways of 1,2-propanediol (1,2-PDO) on platinum were investigated by means of experiments and quantum-mechanical calculations. Different reaction paths on a Pt(111) model surface were computationally screened. Gas and liquid phase products distribution for aqueous phase reforming of 1,2-PDO solutions was experimentally analyzed. A mechanistic approach was used to trace the preferred paths according to calculated activation barriers of the elementary steps; in this way, the presence or absence of some hypothesized intermediates in the experiments was computationally rationalized. Hydroxyacetone was demonstrated to be among the most favored decomposition products. The competit…
Size and Surface Chemistry Tuning of Silicon Carbide Nanoparticles.
2017
International audience; Chemical transformations on the surface of commercially available 3C-SiC nanoparticles were studied by means of FTIR, XPS, and temperature-programmed desorption mass spectrometry methods. Thermal oxidation of SiC NPs resulted in the formation of a hydroxylated SiO2 surface layer with C3Si–H and CHx groups over the SiO2/SiC interface. Controllable oxidation followed by oxide dissolution in HF or KOH solution allowed the SiC NPs size tuning from 17 to 9 nm. Oxide-free SiC surfaces, terminated by hydroxyls and C3Si–H groups, can be efficiently functionalized by alkenes under thermal or photochemical initiation. Treatment of SiC NPs by HF/HNO3 mixture produces a carbon-e…
Electrocatalytic reduction of dioxygen to water by tren-capped porphyrins, functional models of cytochrome c oxidase
1999
International audience; Two different tren-capped porphyrins—in which the two metals, iron and copper, are more or less off-centered—are shown to be efficient catalysts for the reduction of O2 to H2O; surprisingly, their iron-only complexes are shown to be even more effective 4e- catalysts when adsorbed on a graphiteelectrode.
Identification of Active Sites for Oxygen Reduction Reaction on Nitrogen- and Sulfur-Codoped Carbon Catalysts
2019
This research was financially supported by ERA.Net RUS Plus funding mechanism (Project HeDoCat) and by the European Regional Development Fund project TK134.
On the interest of ambipolar materials for gas sensing
2017
International audience; Based on the electrochemical properties of a series of metallophthalocyanines this article shows that the phthalocyanine bearing four alkoxy groups and twelve fluorine atoms behaves approximately as those with eight fluorine atoms. This indicates that the electron-donating effect of one alkoxy group balances the electro-withdrawing effect of one fluorine atom. We engaged three metallophthalocyanines, namely the octafluoro copper phthalocyanine, Cu(F8Pc), an octaester metallophthalocyanine and a phthalocyanine bearing four alkoxy groups and twelve fluorine atoms, Zn(T4F12Pc), in building original conductometric transducers that are Molecular Semiconductor – Doped Insu…
Molybdenum Clusters on a TiO2(110) Substrate Studied by Density Functional Theory.
2009
International audience; A theoretical study on molybdenum clusters adsorbed on a rutile TiO2(110) substrate is reported. Using density functional theory, equilibrium geometries, atomic charges, and total energies have been calculated for clusters containing up to five Mo atoms. Isolated Mo adatoms are strongly oxidized and repel each other. The Mo oxidation state is considerably lowered as soon as the first short Mo−Mo bond is formed. The relative stability of different cluster geometries can be understood from the competition between Mo−Mo and Mo−O bonding. Some low-energy structures for two and three Mo atoms involve large displacements of a substrate oxygen atom. The most stable five-ato…
Investigation of nitrogen and helium cryosorption on molecular sieves
1994
Abstract The helium-containing plasma exhaust gases of Tokamaks can be pumped by cryopumps using cryosorption panels coated with solid porous materials. The best pumping characteristics are achieved with activated charcoal and molecular sieves at temperatures below 10 K. In order to select the most suitable material with respect to cryosorption properties and reactivation behaviour, comparative tests on various molecular sieve types differing in cavity structure, pore size and polarity were carried out. Nitrogen and helium adsorption isotherms were determined at LN 2 temperature and at 14.5 K, respectively, expecting that an extrapolation mechanism between the adsorption properties of both …
Adsorption of p-Xylene/m-Xylene Gas Mixtures on BaY and NaY Zeolites. Coadsorption Equilibria and Selectivities
1997
Coadsorption of the gases p-xylene and m-xylene on BaY and NaY was studied at 150 °C in the range of pressure 10-2-3 hPa. For BaY coadsorption isotherms and single-component adsorption isotherms are perfectly superimposed in the whole range of investigated pressure. The capacity of adsorption of BaY is 3 molecules α-1 for each single component as well as for each mixture under 3 hPa. For NaY coadsorption isotherms lie between those of single p-xylene and m-xylene. The capacity of adsorption of NaY for mixtures is in proportion to the composition of the initial adsorptive mixture and varies from the capacity of adsorption for single p-xylene (3.3 molecules α-1) to that for single m-xylene (3…
Unusual stoichiometry control in the atomic layer deposition of manganese borate films from manganese bis(tris(pyrazolyl)borate) and ozone
2016
The atomic layer deposition (ALD) of films with the approximate compositions Mn3(BO3)2 and CoB2O4 is described using MnTp2 or CoTp2 [Tp ¼ tris(pyrazolyl)borate] with ozone. The solid state decomposition temperatures of MnTp2 and CoTp2 are 370 and 340 C, respectively. Preparative-scale sublimations of MnTp2 and CoTp2 at 210 C/0.05 Torr afforded >99% recoveries with <0.1% nonvolatile residues. Self-limited ALD growth was demonstrated at 325 C for MnTp2 or CoTp2 with ozone as the coreactant. The growth rate for the manganese borate process was 0.19 A˚ /cycle within the ALD window of 300–350 C. The growth rate for the cobalt borate process was 0.39–0.42 A˚ /cycle at 325 C. X-ray diffraction of …
Wear rates and wear mechanisms of alumina-based tools cutting steel at a low cutting speed
1997
Abstract Three ceramic insert materials, zirconia-toughened alumina (Al 2 O 3 –7vol%ZrO 2 ), mixed-based alumina (Al 2 O 3 –TiN–TiC–ZrO 2 ) and alumina reinforced with SiC whiskers (Al 2 O 3 –SiC w ), were used to cut AISI 1040 steel at 3.9 m s −1 . In addition, a traditional grade P10 insert (WC–TiC–Co) was tested. The lifetimes, according to KT/KM and VB B criteria, were determined using a profilometer and by image processing. The worn zones were observed with scanning electron microscopy techniques. Adhesion and plastic deformation were dominant wear mechanisms in zirconia-toughened alumina, mixed-based alumina and sintered carbide P10, both in the craters and in the cutting edges. As we…