Support-induced promotional effects on the activity of automotive exhaust catalysts 1. The case of oxidation of light hydrocarbons (C2H4)

The kinetics of oxidation of a light hydrocarbon (C₂H₄) were studied on catalysts comprising of combinations of one of three metals, Pt, Pd or Rh supported on five different supports, that is, SiO₂, γ-Al₂O₃, ZrO₂ (8% Y₂O₃), TiO₂ or TiO₂ (W⁶⁺). Significant variation of turnover frequency with the carrier was observed, which cannot be explained by structure sensitivity considerations and is attributed to interactions between the metal crystallites and the carrier. The catalytic activity of these metal-support combinations was investigated over a wide range of partial pressures of ethylene and oxygen. In a separate set of experiments, the kinetics of C₂H₄ oxidation were also investigated on polycrystalline Rh films interfaced with ZrO₂ (8 mol% Y₂O₃) solid electrolyte in a galvanic cell of the type: C₂H₄, O₂, Rh/YSZ/Pt, air, during regular open-circuit conditions as well as under Non-Faradic Electrochemical Modification of Catalytic Activity (NEMCA), that is, closed-circuit conditions. Up to 100-fold increase in catalytic activity was observed by supplying O²⁻ ions to the catalyst surface via positive potential application to the catalyst. The observed kinetic behavior upon increasing catalyst potential parallels qualitatively the observed alteration of turnover frequency with variation of the support of the Rh crystallites.     

Perceptual consequences of an illness-concern induction and its relation to hypochondriacal tendencies.

This article examines the perceptual consequences of activating illness concern as a function of hypochondriacal tendencies. In 2 independent samples, hypochondriacal tendencies were associated with slower reaction times on a modified emotional Stroop task when the stimulus words were illness related, but only when illness concern was activated. Moreover, these findings emerged when hypochondriacal tendencies were defined as a sensitivity to bodily sensations. When defined as illness preoccupation and fear, hypochondriacal tendencies were associated with a generalized pattern of perseveration to all stimuli when health concern was activated. Finally, the results persisted even after statistically controlling for state anxiety. Findings are discussed within the context of an activation hypothesis and highlight the importance of the operational definition and assessment of hypochondriacal tendencies when examining perceptual biases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Carbon nanofibres and activated carbon nanofibres as electrodes in supercapacitors

Carbon nanofibres have been prepared by a floating catalyst procedure at industrial scale in a metallic furnace. The nanofibres (50-500 nm diameter and 5-200 μm length) are grown from the Fe particles used as catalyst. Soot appears together with the carbon nanofibres. The sample has been chemically activated using KOH as activating agent. Scanning electron microscopy has shown a smooth surface for the as-prepared carbon nanofibres but a rough surface for the activated ones. The specific surface area increases from 13 to 212 m²/g due to the activation. The volume of the micropores (in the 1-2 nm range) and the mesopores (2-5 nm range), as deduced by density functional theory methods, also increases after the activation. Electrochemical behaviour of the as-prepared and activated carbon nanofibres has been tested in a supercapacitor at laboratory scale using 6 M KOH aqueous solution as electrolyte. The specific capacitance, which is less than 1 F/g for the as-prepared sample, increase up to ≈60 F/g for the activated sample. Only a slight decrease in capacitance has been observed as the current density increases. Specific power of ≈100 W/kg at specific energy of 1 Wh/kg has been found in some particular cases. We have compared the electrochemical parameters of our activated carbon nanofibres with those of activated carbon nanofibres coming from a commercial sample; the latter was activated by the same way as our sample.     

Stabilisation of lithiated graphite in an electrolyte based on ionic liquids: an electrochemical and scanning electron microscopy study

1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) is shown to reversibly permit lithium intercalation into standard TIMREX^® SFG44 graphite when vinylene carbonate (VC) is used in small amounts as additive. The best performance was obtained when 5% of VC was added to a 1 M solution of LiPF₆ in EMI-TFSI. Intercalation of lithium in the SFG44 graphite host was demonstrated over 100 cycles without noticeable capacity fading. The reversible charge capacity was around 350 mA h g⁻¹ and an only small irreversible capacity loss per cycle could be observed. Li₄Ti₅O₁₂ was used as counter electrode material. Scanning electron microscopy indicates the reduction of the electrolyte without graphite exfoliation in the neat electrolyte and the formation of a passivation film in the case of a VC-containing electrolyte. Other additives that were tested comprise ethylene sulphite and acrylonitrile which show also a positive effect, but a smaller one than vinylene carbonate. LiCoO₂ positive electrodes were cycled in a 1 M solution of LiPF₆ in EMI-TFSI with good charge capacity retention over more than 300 cycles, when Li₄Ti₅O₁₂ was used as counter electrode. The formation of a passivation film is proven on the LiCoO₂-electrodes, when the electrolyte contained VC, but not in the neat ionic liquid. Finally, the stable cycling of a full cell configuration is proven in this electrolyte system. An ammonium-containing ionic liquid (methyltrioctylammonium-bis(trifluoromethylsulfonyl)-imide, MTO-TFSI) is shown to permit the cycling of both, graphite and lithium cobalt oxide when VC is used as additive in small amounts, but at slightly elevated temperatures.     

Group 15 element-graphite composites synthesized by reduction of chlorides by KC8: Characterization and electrochemical lithiation

Group 15 element-graphite M/C composites were prepared by reduction of MCl_x chlorides (AsCl₃, SbCl₅, BiCl₃) by KC₈ in THF. Arsenic and antimony were both amorphous: antimony appeared as a film-like material, formed of aggregated nano-sized particles covering parts of the graphite surface; arsenic was present as large graphite supported particles. On the contrary, bismuth was present as crystalline metal nanoparticles distributed on the graphite surface. Amorphous As and Sb-graphite composites displayed stable reversible capacities of 310 and 420 mA h/g, respectively while that of crystalline Bi-graphite materials decreased regularly upon cycling. Although these practical capacities were lower than the expected theoretical ones corresponding to the formation of Li₃M compounds, it appeared that, in the presence of graphite, amorphous solids exhibiting a (partly) covalent character like As and Sb gave better long life cycling properties than the crystalline and metallic bismuth. It was very likely that our one step synthesis could generate bonds between graphite and (partly) covalent solids reducing consequently the volume expansion effects occurring during cycling. On the contrary, metallic solids like bismuth that were not inclined to bond with graphite behave, upon cycling, as corresponding massive metals.     

Electrochemical catalytic modification of activated carbon fabrics by ruthenium chloride for supercapacitors

A novel method, electrochemical catalytic oxidation via a ruthenium redox couple in an aqueous RuCl₃ · xH₂O solution rather than the anodic deposition of Ru oxides, was developed to modify the microstructure and electrochemical properties of activated carbon fabrics (ACFs). The variation in microstructures (i.e., specific surface area and mean pore size) for the modified ACFs was examined by means of nitrogen gas adsorption isotherms. The distribution of oxygen-containing functional groups within the modified ACFs was identified by temperature programmed desorption (TPD) and X-ray photoelectron (XPS) spectra. Effects of the electrochemical catalytic modification on the electrochemical characteristics and reversibility of ACFs were investigated systematically by means of cyclic voltammetry (CV) and chronopotentiometry (CP) in 0.5 M H₂SO₄. The total specific capacitance of ACFs reached a maximum (ca. 180 F/g measured at 10 mA/cm²) when they were catalytically modified at 1.15 V with a passed charge density of 5 C/cm². These modified ACFs were demonstrated to be an excellent candidate for the supercapacitor application.     

Electrodeposition mechanism of hydrogen-free diamond-like carbon films from organic electrolytes

A brief introduction on the development of electrodeposition of diamond-like carbon (DLC) films was given, and our experiments were done, emphasizing on how to deposit hydrogen-free DLC films. Methanol, acetonitrile and N,N-dimethyl formamide (DMF) were chosen as electrolytes, while Si and conductive glass were used as substrates. The sample deposited on Si through methanol was the only one in this comparative research that produced hydrogen-free DLC film as it was indicated by the FTIR spectroscopy. Two explanations, based on reaction mechanism, were proposed to explain this fact. It was believed that the reaction rate and the effect of hydroxyl groups in the molecules of the electrolytes played important roles in the deposition of hydrogen-free DLC films.     

Role of surface chemistry on electric double layer capacitance of carbon materials

A large number of porous carbon materials with different properties in terms of porosity, surface chemistry and electrical conductivity, were prepared and systematically studied as electric double layer capacitors in aqueous medium with H₂SO₄ as electrolyte. The precursors used are an anthracite, general purpose carbon fibres and high performance carbon fibres, which were activated by KOH, NaOH, CO₂ and steam at different conditions. Among all of them, an activated anthracite with a BET surface area close to 1500 m²/g, presents the best performance, reaching a value of 320 F/g, using a three-electrode system. The results obtained for all the samples, agree with the well-known relationship between capacitance and porosity, and show that the CO-type oxygen groups have a positive contribution to the capacitance. A very good correlation between the specific capacitance and this type of oxygen groups has been found.