Synthesis and photocatalytic properties of HTaWO6/(Pt,TiO2) and HTaWO6/(Pt,Fe2O3) nanocomposites

HTaWO₆/(Pt,TiO₂) and HTaWO₆/(Pt,Fe₂O₃) nanocomposites were synthesized by successive intercalation reactions of HTaWO₆ with [Pt(NH₃)₄]Cl₂ aqueous solution, n-C₃H₇NH₂/n-heptane mixed solution and acidic TiO₂ colloid solution or [Fe₃(CH₃CO₂)₇(OH)(H₂O)₂]NO₃ aqueous solution followed by UV light irradiation. The gallery heights of HTaWO₆/(Pt,TiO₂), HTaWO₆/TiO₂, HTaWO₆/(Pt,Fe₂O₃) and HTaWO₆/Fe₂O₃ was less than 0.51 nm. The host HTaWO₆ was white possessing band gap energy of 3.1 eV, whereas HTaWO₆/Pt, HTaWO₆/(Pt,TiO₂), HTaWO₆/Fe₂O₃ and HTaWO₆/(Pt,Fe₂O₃) were yellow and showed broad reflection over 400–600 nm together with that corresponding to the host layer. Photocatalytic activities of HTaWO₆/TiO₂ and HTaWO₆/Fe₂O₃ were superior to those of unsupported TiO₂ and Fe₂O₃ and were greatly enhanced by co-incorporation of Pt. HTaWO₆/Pt, HTaWO₆/(Pt,TiO₂), HTaWO₆/Fe₂O₃ and HTaWO₆/(Pt,Fe₂O₃) showed photocatalytic activity.     

Transformation of C6 hydrocarbons over sulfated zirconia catalysts

The conversion of the C6 saturated hydrocarbons hexane, methylcyclopentane and cyclohexane was studied in a flow microreactor in the temperature range 120–240°C. Sulfated zirconia with different sulfate contents were used as catalysts. Catalysts were characterized before and after reactant exposure using Raman spectroscopy and XPS. The obtained results confirm data on the reaction mechanism already reported in the literature. The first step is the hydrogen abstraction which could occur to a more or less advanced extent as a function of the sulfate density species. This process is the main cause of the catalyst reactivity but also of the catalyst deactivation. More advanced dehydrogenated species lead to polymerized species which remain strongly chemisorbed on the catalyst surface. XPS data also indicated that during these redox processes a part of the sulfur remained on the catalysts surface. Higher sulfate densities lead to the cyclization of hexane.     

Sintering of Cr2O3 in H2/H2O Gas Mixtures

Sintering of Cr₂O₃ was performed at 1530°C under low pO₂ close to the Cr–Cr₂O₃ equilibrium generated by H₂/H₂O gas mixtures. Addition of 1 wt%ZrO₂ and 0·1 wt%MgO increases the density of Cr₂O₃ from 97% TD to nearly full density. Rapid densification and the higher density are attributed to the appearance of a transient CrO liquid phase as a result of the presence of ZrO₂ and MgO under the sintering conditions. A grain size reduction is also achieved owing to the presence of ZrO₂ particles and the possible formation of a MgCr₂O₄ spinel at grain boundaries. There is no connection between densification and loss of material due to evaporation. ©     

Polypyrrole/thermally sensitive polyelectrolyte composite (I)

Polypyrrole (PPy) was prepared by electrochemical polymerization with the polyelectrolyte (PE) as a dopant. The PEs were copolymers of the water soluble polymers and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). The water soluble polymers were thermally sensitive poly(N-isopropyl acrylamide), P(NiPAAm) and thermally insensitive poly(acrylamide), P(AAm). The surface of PPy/PE film observed by SEM was smoother than that of PPy film doped with a monoelectrolyte. PPy/PE composites were fairly conductive, whose electrical conductivities measured by the four-probe method were in the range of 10⁻¹ to 10⁻² S/cm. The characteristics of cation and anion exchange during redox processes were investigated by applying potential from −0.8 to 0.5 V vs. an Ag/AgCl reference electrode to the PPy. The effect of temperature on the doping–dedoping behavior and mass change of PPy composites was investigated by potentiodynamic voltammetry and electrochemical quartz crystal microbalance (EQCM). The electrochemical activity of the PPy/PE gradually decreased with increasing temperature. PPy/P(NiPAAm/AMPS) showed much greater mass change with increasing temperature than PPy/P(AAm/AMPS), mainly because of a decrease in the degree of swelling of thermally sensitive moiety. This confirms that PPy/P(NiPAAm/AMPS) possesses temperature-dependent electrochemical activity, which indicates that it can be utilized for many attractive applications. The thermal volume transition temperature of PPy/P(NiPAAm/AMPS) was estimated from the slope change of mass decrease. The transition temperature of the oxidized state of PPy/P(NiPAAm/AMPS) was higher than that of the reduced state.     

The isothermal section at 400°C of the Nd–Cu–Sn ternary system

The Nd–Cu–Sn isothermal section at 400°C has been investigated by means of X-ray diffraction, optical and scanning electron microscopy and electron probe microanalysis. The following compounds have been identified or confirmed: NdCu₅Sn, Nd₇Cu₃₅Sn₁₁, NdCu₉Sn₄, NdCuSn, Nd₃Cu₄Sn₄, NdCu₂Sn₂, Nd₂Cu₃Sn₆ and NdCu_1−ySn₂, and their crystal structure have been determined or revised. Single crystal structure determination of the phases Nd₇Cu₃₅Sn₁₁ and Nd₃Cu₄Sn₄ and full profile powder refinement of the compound Nd₂Cu₃Sn₆, previously suggested as Nd₂Cu₄Sn₅, are also given. The subdivision of the composition triangle in tie triangles has been nearly completed. Of the predicted 36 three-phase equilibria, thirty have been defined. The general characteristics of the section have been discussed in comparison with those of other R–Cu–Sn systems formed by light rare earths (R= Ce, Pr).     

Effect of hydrogen pressure on the combustion synthesis of Mg2NiH4

The aim of this work is to study the experimental production of a hydrogen storage alloy (Mg₂NiH₄) directly from a magnesium and nickel mixture without activation treatment by combustion synthesis in hydrogen. In this paper, the effect of hydrogen pressure on the hydriding combustion synthesis of Mg₂NiH₄ at 0.5, 1.0, 2.0 and 4.0 MPa has been studied by differential scanning calorimeter (DSC) and by X-ray diffraction (XRD). The XRD results showed that the combustion products of all samples were composed mainly of Mg₂NiH_0.3 and Mg₂NiH₄ in spite of a slight remainder of Ni, in which the amount of Mg₂NiH₄ increased with increasing hydrogen pressure, but not very drastically. In addition, the DSC results showed several sharp heat-flow peaks during heating and cooling periods between room temperature and 850 K. It is suggested that the reaction mechanism of the hydriding combustion synthesis is not simple, but complicated with several endothermic and exothermic reactions with pressure dependence.     

A triheterometallic cluster: synthesis and structural characterisation of a cyclopentadienyl-substituted pentanuclear cluster based on an Os3CoRu metal core

The ionic coupling of the carbonyl cluster anion [Os₃Co(CO)₁₃]⁻ (1) with [Ru(η⁵-C₅H₅)(NCMe)₃]⁺ affords the new pentanuclear triheterometallic cluster Os₃CoRu(CO)₁₃(η⁵-C₅H₅) (2) as well as the known bimetallic cluster compounds HOs₃Ru(CO)₁₁(η⁵-C₅H₅) and Os₃Ru₂(CO)₁₁(η⁵-C₅H₅)₂. The crystal structure of cluster 2 shows that the metal framework is based on a trigonal bipyramid (approximate C_s symmetry) with the Ru, Co and an Os atom occupying the equatorial metal plane.     

Analysis of an irreversible Ericsson engine with a realistic regenerator

An internally irreversible Ericsson engine, with a realistic regenerator, has been analyzed. The study considers internal irreversibilities with the introduction of turbine and compressor thermal-efficiencies and pressure-drops present in realistic regenerators. The effects of internal irreversibilities on the power output and thermal efficiency of the cycle have been determined using the finite-time thermodynamics. Maximum power-density, rather than maximum power, was used as the criterion for optimization, with the objective of having a more efficient small-sized engine.