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This paper reports on an investigation using steady-state isotopic transient kinetic analysis (SSITKA) of Al2O3-promotion of sulfated zirconia (SZ) for n-butane isomerization. SZ promoted with Al2O3 showed an approximately 30% increase in n-butane isomerization activity at 250 °C. The average surface residence times of the reaction intermediates on unpromoted and Al2O3-promoted SZ measured by SSITKA suggest that the active sites on both catalysts were identical. There was, however, a significant increase in the concentration of surface intermediates upon Al2O3-promotion, leading to the increased activity. Al2O3-promotion also appeared to improve catalyst site stability resulting in a slower rate of deactivation.

X-ray absorption in combination with powder X-ray diffraction and surface analytical studies were performed in order to investigate the chemical state, local order and spatial distribution of Ti in sodium alanate doped with TiCl3 and small Ti clusters. Kinetic investigations of the different hydrogenation and dehydrogenation steps of doped NaAlH4 indicate a nucleation and growth mechanism as rate limiting step in the transformation of the material. The results support a mechanism where Ti has an accelerating effect on the phase transformation, probably by introducing non-thermal defects into the material.

In the present work we study the nanocrystalline powders of lanthanide-doped Gd3Ga5O12 (GGG, gadolinium gallium garnet) prepared using propellant synthesis. A series of GGG samples containing a number of different trivalent lanthanide ions (Tm, Er, Ho, Eu, Sm, Nd, and Pr) in different quantities (1%, 5%, 10%) were produced. Samples were characterized by X-ray diffraction (pre- and post calcination) for phase identification and line-broadening analysis, and by electron microscopy (SEM and TEM) for morphological and nanostructural investigation. Thermal behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The samples have a polycrystalline porous structure. Elemental microanalysis made by energy dispersive X-ray spectroscopy (EDX) detector attached to TEM and XRD unit-cell determinations confirmed that the lanthanides ions entered the structure of GGG. Crystallites have a high degree of disorder.

The preparation of a series of niobium-based aerogel samples under acidic and basic conditions is reported. The effect of the matrix (SiO 2 , Al 2 O 3 , ZrO 2 ) and of the gelation conditions (acidic or basic) on the surface area, the porosity, and the catalytic activity of the solids in the oxidation of different substrates with hydrogen peroxide is investigated. The amount of niobium is constant in all samples. The oxidation of unsubstituted (cyclooctene) and substituted (geraniol, nerol, and trans-2-pentene-1-ol) olefins is studied. The catalysts are moderately active but produce epoxides in good yields. The latter are influenced by the matrix properties (surface acidity and surface area). The preparation method makes it possible to prepare catalysts that are resistant to leaching and can be recycled several times without appreciable loss of activity.

Transition element nanoclusters embedded in dielectric matrix are important for their optical and magnetic properties. In this work, composite silica films with cobalt atomic concentration up to 10% were synthesized by radiofrequency (rf) magnetron co-sputtering deposition technique. The composite systems structure could be triggered by varying the deposition parameters and by using a subsequent thermal treatment to promote the nanocluster formation. Magnetic measurements showed that the embedded cobalt nanoparticles act as superparamagnets, with coercive field and blocking temperature related to their size and structure (hcp or fcc).

Contradictory results about the best oxidic precursor of Fe ammonia synthesis catalyst prompted the present comparative investigation on wustite- and magnetite-based catalysts. Many physical (density, porous texture, crystalline phases, reduction rate, metal surface, abrasion loss) and catalytic (kinetic constants, thermoresistancy) properties have been determined on both catalysts. The wustite-based catalyst proved to be much more active, especially at lower temperatures, approaching the performances of Ru/C catalyst, except at high conversion. Possible reasons for such a behavior of the wustite-based catalyst are discussed, suggesting that a reconsideration of the present consolidated knowledge on Fe ammonia synthesis catalyst might be convenient.

A polydomain internal structure was evidenced by means of High Resolution Transmission Electron Microscopy (HRTEM) in palladium nanoparticles of two 5% Pd/SiO2 catalysts prepared by impregnation technique. Such poly-domain structure biased the line broadening analysis of the XRPD patterns, from which highly underestimated average diameters were obtained in comparison to those measured by means of Transmission Electron Microscopy (TEM).

Following our previous papers regarding Pd/C and Pd/SiO2 catalysts, the determination of the Pd/CO average chemisorption stoichiometry from experimental data has been extended to the Pd/alumina system. To this purpose, the Pd crystallite size determined by the well-established line-broadening (LB) method, using X-ray powder diffraction (XRPD) associated with the Fourier analysis of suitable best-fitted peak profiles, and the chemisorbed CO volume, determined by the pulse flow method, were employed. HRTEM was also used to check the structural features of the Pd particles, which proved to be monodomains of cubooctahedral shape. A high-dispersion 5 wt % Pd/alumina catalyst was prepared by impregnation and thermally treated at different temperatures up to 1073 K. Even at this high temperature a good Pd dispersion was retained. A suitable subtraction of the X-ray scattering, due to the support, was done to obtain the real profile of the supported metal, from which the surface-weighted average particle diameter...

One of the major areas of research in nanomedicine is the design of drug delivery systems with remotely controllable release of the drug. Despite the enormous progress in the field, this aspect still poses a challenge, especially in terms of selectivity and possible harmful interactions with biological components other than the target. We report an innovative approach for the controlled release of DNA, based on clusters of core–shell magnetic nanoparticles. The primary nanoparticles are functionalized with a single-stranded oligonucleotide, whose pairing with a half-complementary strand in solution induces clusterization. The application of a low frequency (6 KHz) alternating magnetic field induces DNA melting with the release of the single strand that induces clusterization. The possibility of steering and localizing the magnetic nanoparticles, and magnetically actuating the DNA release discloses new perspectives in the field of nucleic-acid based therapy.

TiO2–SiO2 composites containing 10 wt%, 20 wt%, 30% and 40 wt% of TiO2, obtained by using preformed mesoporous silica nanoparticles (MSNs) and titanium isopropoxide as titanium source, have been investigated in detail using a variety of techniques. All the samples were characterized by N2-physisorption, X-ray powder diffraction (XRPD), diffusive reflective UV-vis spectroscopy (DRUV-vis), X-ray photoelectron spectroscopy (XPS) and imaged using transmission electron microscopy (TEM). The TiO2–MSN composites, that exhibited a spherical morphology, high specific surface areas and titania in the anatase phase, owing to their specific chemical–physical properties were studied as catalysts in the photocatalytic degradation of methylene blue, methyl orange and paracetamol, as examples of polluted wastewaters. The well-defined porous structures of MSNs may offer a special environment for titania nanoparticles, increasing the specific surface area and the thermal stability of the composite, thus modifying the photocatalytic behavior of the materials. The TiO2 loading, the particle size and the surface characteristics were related to the degree of UV absorption and the measured energy band gap of the nanocomposites. A cooperative effect between the two components (TiO2 and SiO2) could be the key factor at the basis of the good photocatalytic performances: nanostructured TiO2 in intimate contact with MSN provides the sites for generation of OH˙ radicals by oxidation of water and the SiO2 skeleton is able to adsorb the molecules of cationic dyes and prevent poisoning of the TiO2 surface.

Bimetallic Ag/Pd nanoparticles were fabricated by laser ablation of a silver target in water and successive addition of palladium nitrate to promote a partial galvanic replacement of silver with palladium. The obtained nanoparticles, as shown by a microscopic investigation coupled with EDX and SAED analysis, exhibit a silver core, able to produce SERS enhancement, and a Pd cloudy shell at the surface that can interact with organic molecules in catalytic reactions. The test was carried out using as a molecular probe an aromatic nitroderivative, which, by adsorption on the metal substrate, undergoes an almost total reduction to azoderivate, as evidenced by the comparison between the SERS spectra recorded on pure Ag and Ag@Pd nanoparticles. © 2013 Elsevier B.V. All rights reserved.

Pd catalysts on different supports (active carbon, silica, alumina) were studied for the selective hydrogenation of benzaldehyde to benzyl alcohol. They were characterized by TPR, CO chemisorption and XRD. Batch hydrogenation tests were performed before and after sulfur poisoning. Strong metal–support interaction was found for Pd/alumina, giving high Pd dispersion. Chemisorption stoichiometry Pd/CO=2 was confirmed again. While Pd/C has the highest activity for benzaldehyde hydrogenation, a satisfactory selectivity to benzyl alcohol requires an oxidic carrier or proper sulfur poisoning of Pd/C.

The mechanical treatment of a Al75Mo25 mixture of pure elemental powders in a high-energy mixer mill induces partial solid state reactivity and solid solution formation. This is suggested by a quantitative phase evaluation and by the changes of Al lattice parameter carried out with Rietveld analysis of diffraction patterns collected after extended time of processing (4, 8, 16, 32, 57, and 78 h). The small angle neutron scattering experiments showed that diffusion processes are the rate-controlling step for these solid state reactions. The formation of metastable phases is confirmed by in situ neutron diffraction annealing experiments on selected as-milled powders. In the specimen mechanically alloyed for 4 h, Al12Mo phase is formed at 590 °C (below the aluminum melting point). Soon after this temperature, the remaining Al is consumed to form the Al8Mo3 phase. In the alloy mechanically treated for 32 h, the Al12Mo phase appears after annealing at 430 °C, while the Al8Mo3 phase is found at 493 °C. After the...

Aim of the paper is to apply a modified version of the Rietveld method to two Au–Pd/C catalysts prepared by successive impregnation and reduced in situ by a special holder in order to show that a suitable WAXS analysis, performed in routine lab and using an X-ray conventional generator, can be very detailed and rich of information especially when a bimetallic catalyst has to be considered.

This study uses X‐ray diffraction (XRD) techniques to investigate the nanostructural features of a series of four Pd/C catalysts, which had the same load, 0.51 ± 0.02 wt%, as palladium, with significantly different dispersions, obtained by applying different temperature ageings up to 873 K. By means of a Rietveld refinement, performed using a special fitting procedure, which takes into account the various contributions to the background scattering, the palladium fraction due to nanoparticles or clusters smaller than about 20–25 A could be determined. We have compared this Rietveld (absolute) quantitative method with a simpler, but less precise, single‐peak (relative) XRD analysis, interesting for fast industrial applications. The Pd fractions due to nanoparticles, as determined by the two methods, are close each other for all samples investigated, apart from one for which the disagreement is near 20%.

Neutron diffraction patterns, collected at room temperature and, within situthermal treatment, from 981 to 1173 K, on a zirconia sample containing 3 wt% of sodium, show the presence and the stability of the cubic form of zirconia from 298 to 1073 K. The analysis has also demonstrated the presence of a significant amount of the tetragonal form of zirconia, which cannot be clearly detected using conventional X-ray diffraction. We report and discuss the Rietveld refinements performed on the samples, analysed at 298 and at 981 K. The cubic form appears to be stabilized by the incorporation of sodium ions, which randomly replace the zirconium ions, thus forming a substitutional solid solution.

Using x-ray Rietveld analysis the fcc (fluorite-type) structure of a Na-containing nanocrystalline zirconia powder (9.5 nm estimated of crystallite size) obtained by precipitation and subsequent calcination has been confirmed. The result shows that using conventional x-ray diffraction techniques the cubic crystallographic form of ZrO{sub 2} from the tetragonal one in nanosized powders. These conclusions are supported by the findings of independent Raman scattering experiments. {copyright} {ital 1997 Materials Research Society.}

International audience; Transition metal-based lithium orthosilicates (Li2MSiO4, M=Fe, Ni, Co, Mn) are gaining a wide interest as cathode materials for lithium-ion batteries. These materials present a very complex polymorphism that could affect their physical properties. In this work, we synthesized the Li2FeSiO4 and Li2MnSiO4 compounds by a sol-gel method at different temperatures. The samples were investigated by XRPD, TEM, Li-7 MAS NMR, and magnetization measurements, in order to characterize the relationships between crystal structure and magnetic properties. High-quality Li-7 MAS NMR spectra were used to determine the silicate structure, which can otherwise be hard to study due to possible mixtures of different polymorphs. The magnetization study revealed that the Neel temperature does not depend on the polymorph structure for both iron and manganese lithium orthosilicates.

The commercially available ion-exchange resin Amberlite IR120 has been used as the stabilizing agent for the preparation of a size controlled nanostructured hematite phase. The employed synthetic approach, based on the loading of Fe3+ by ion exchange and the subsequent treatment with an aqueous base solution, produces a nanocomposite material with a remarkably high content of oxide nanoparticles (iron content = 18.8% w/w, corresponding to 24.9% w/w of Fe2O3). Scanning electron microscopy and energy dispersive X-ray spectroscopy investigation show that the iron distribution is egg-like and parallels the distribution of the sulfonic groups of the ion-exchanger. Transmission electron microscopy characterization reveals that the size of the ferric oxide nanoparticles in the nanocomposites is narrowly distributed in the 4-6 nm range and that it is the same after the first and the fifth ion-exchange-precipitation cycle. Selected area Electron Diffraction (SAED) analysis of the nanostructured oxide after five ion-exchange-precipitation cycles indicates that it is hematite with a distorted structure.

We have prepared, for the first time, stable and uncapped Ag/Cu-based bifunctional nanoparticles (NPs) (BFNPs) in water, by combining ps laser ablation in liquid environment and galvanic replacement. The particles were obtained in a single step by 1,064 nm irradiation of a Cu target in water solutions of AgNO3 or AgNO2. Under proper salt concentration and irradiation conditions, the laser beam activates formation of deep orange colloids, which are positively charged and stable for weeks. High resolution transmission electron microscopy (HRTEM) analysis showed a predominance of composite crystalline nanostructures with size in the 1-15 nm range and consisting of fcc Ag and fcc Cu (or its oxides). While CuO tenorite crystalline phase was detected by HRTEM, X-ray photoelectron spectroscopy analysis permitted to observe also the Cu(I) oxidation state of Cu, being the Cu(I)/Cu(II) ratio different in the samples obtained in AgNO3 or AgNO2 baths. Functionalization with organic ligands and subsequent Raman tests demonstrated the SERS activity of the BFNPs and the existence of different complexing surface sites.

On the basis of known equations for calculating X-ray diffraction intensities from a given number of unit cells of a crystal phase in polycrystalline material, as due to: (i) Bragg reflections; (ii) average diffuse scattering caused by thermal plus first-kind disorder; and (iii) incoherent scattering, a relationship has been found that ties, in the Rietveld analysis, the Bragg scale factor to a scale factor for `disorder' as well as incoherent scattering. Instead of fitting the background with a polynomial function, it becomes possible to describe the background by physically based equations. Air scattering is included in the background simulation. By this means, the refinement can be carried out with fewer parameters (six fewer than when a fifth-order polynomial is used). The DBWS-9006PC computer program written by Sakthivel & Young [(1990), Georgia Institute of Technology, Atlanta, GA, USA] has been modified to follow this approach and it has been used to refine the crystal structures of the cubic form of Y2O3 and of α-Al2O3. Peak asymmetry has been described by a function based on an exponential approximation. The results from refinements using polynomial physically based background function are, in terms of final structural parameters and reliability indices, very close to each other and in agreement with results reported in the literature. The reconstruction and optimization of the background scattering by means of physically based equations helps the implementation in the Rietveld code of other possible specific diffuse scattering contributions, such as that due to an amorphous phase.

Rietveld analysis has enabled a determination, by an internal approach, of the degree of crystallinity of a sample of polyethylene terephthalate (PET) and three samples of zirconium oxide obtained by precipitation from ZrOCl2 followed by crystallization at a different temperature. After subtraction of the air scattering, a global diffuse scattering produced by the amorphous phase, by the thermal and lattice disorder and, lastly, by the incoherent or Compton scattering, was built up in the frame of the DBWS-9006PC computer program written by Sakthivel & Young [(1990), Georgia Institute of Technology, Atlanta, GA, USA], modified as described by Riello, Fagherazzi, Clemente & Canton [J. Appl. Cryst. (1995), 28, 115–120]. All these contributions (and the corresponding scale factors) were simultaneously optimized, together with the crystalline peak profiles. On the basis of the modified Rietveld analysis, an equation has been suggested that calculates the degree of crystallinity. The value found in the examined PET sample is very close to that already calculated [Polizzi, Fagherazzi, Benedetti, Battagliarin & Asano (1990). J. Appl. Cryst. 23, 359–365] with a nonstructural fitting procedure.

It is well known that the structure of ZrO2 powder synthesized by low temperature calcination of hydrous zirconia is strongly affected by the nature and properties of precursors. In the present paper, we combined a precipitation/restructuring approach (bottom-up/top-down methodology) to produce zirconium hydroxide nanoparticles that transform into stable nanophasic tetragonal zirconia by low temperature calcination. The dimension and structure of precursors could be modulated by adjusting pH. The synthetic route was investigated by Raman spectroscopy, X-Ray Diffraction, Small-Angle X-Ray Scattering and High-Resolution Transmission Electron Microscopy. The zirconium hydroxide nanoparticles represent the final product of the overall process, which starts as a bottom-up synthesis of the hydroxide gel, followed by a top-down reorganization stage. During this rearrangement, the evolving structure passes through a mass fractal that arises from the clustering of the primary zirconium hydroxide nano-units.

Catalytic reforming of CH4 with CO2 was investigated on mono and bimetallic Pd(or Pt)-Ni based samples supported on Al2O3 and ZrO2. A simple temperature-programmed procedure was used to study both reforming and coke formation via CH4 or CO decomposition. Catalysts supported on zirconia are more active than alumina-supported samples. The addition of Pt or Pd to Ni/ZrO2, preferably by co-impregnation, prevents coke formation. The co-impregnated Ni-Pd/ZrO2 catalyst looks the most promising for a possible industrial application.

Synthesis of gold nanoclusters inside strongly acidic ion exchangers, in beaded forms, is carried out under different conditions. After metallation with [Au(en) 2 ]Cl 3 and reduction with H 2 in the absence of any added aqueous phase, Au 0 / -SO 3 H nanocomposites are produced that are compared with Au 0 / -SO 3 − Na + ones obtained with NaBH 4 as reductant in aqueous medium. Reduction conditions allow control of both distribution and size of the metal nanoclusters. Metal distribution inside the polymer beads appears to be quite homogeneous under the hydrogen reduction conditions and metal nanoclusters size turns out to be size-controlled in the 3–5 nm range. In the case of the action of NaBH 4 in water, metal distribution inside the polymer beads appears to be quite peripheral and the metal nanoclusters turn out to be size-controlled but definitely larger, 5–7 nm, than those obtained by action of molecular hydrogen.

Nanoporous gold (NPG) layers have been fabricated by silver leaching of Ag–Au alloys with different dealloying processes and working temperatures. Structural, compositional and optical properties of the different samples have been analyzed with several experimental techniques: scanning and transmission electron microscopy (SEM/TEM), electrochemical impedance spectroscopy (EIS), Rutherford back scattering (RBS), spectroscopic ellipsometry. A periodic pattern has been realized on samples surface with focused ion beam (FIB) lithography in order to exploit NPG metallic behavior for surface plasmon polaritons (SPPs) excitation. The plasmonic response of the several NPG gratings has been analyzed and related to structural properties and fabrication conditions.

Pd-Fe/SiO2 bimetallic catalysts with a constant amount of Pd and a different Fe/Pd ratio were prepared by sequential wet impregnation and the hydrogenation of 2,4-dinitrotoluene was carried out at 25°C in a batch reactor. The presence of Fe enhances the Pd catalytic activity. The formation of a dispersed Pd-Fe alloy was evidenced through X-ray powder diffraction and is consistent with the data observed by FTIR analysis, TPR, and chemisorption features. The increase of the Fe total content of the catalysts results in the increase of the dispersion of the metallic phase and in the presence of partially oxidized Fe species. FTIR analysis shows that nitrocompounds chemisorb mainly on the support rather than on the metal surface. It is suggested that the Pd-Fe alloy formation is responsible for the increase of the catalytic activity because of a cooperative effect of Fe in the hydrogen transfer step.

The polymer framework of water-swollen copolymers of N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid, and ethylenedimethacrylate (nominal cross-linking degrees of 4, 8, and 20 mol %) is composed of highly expanded domains, with "pores" not less than 6 nm in diameter. When the 4% cross-linked copolymer (DAE 26-4) is swollen with a 10(-4) M solution of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) in water, MeOH, EtOH, or nBuOH, the molecules of the paramagnetic probe rotate rapidly (τ

Hydrogen production by steam reforming of methanol and ethanol is studied over a series of Cu/ZnO/Al(2)O(3) catalysts prepared by different coprecipitation procedures and modified with the introduction of Ni and Co. The catalysts are characterized using N(2) physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR) techniques, N(2)O decomposition, high resolution transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). Despite the influence of the preparation method on the texture and structure of Cu/ZnO/Al(2)O(3) catalysts, their catalytic behavior appears not significantly affected. While Cu/ZnO/Al(2)O(3) shows poor H(2) selectivity in the ethanol steam reforming reaction, the presence of a second metal (Ni or Co) significantly improves the reforming reaction. Although coke deposition remains a drawback for these systems, formation of an alloy between Ni and Cu appreciably reduces carbon deposition with respect to the Co/Cu-based system. (C) 2010 Elsevier B.V. All rights reserved.

We report a facile strategy to obtain multiwalled carbon nanotubes (MWCNTs) functionalized with covalently bonded lysozyme. The functionalization procedure has been investigated by means of several techniques, including thermogravimetry, Raman spectroscopy, transmission electron microscopy, and cyclic voltammetry. A functionalization of about 1 lysozyme molecule every 4000 carbon atoms is obtained. The modified lysozyme-CNTs nanocomposite shows a significant increase of the antibacterial activity towards the Gram-positive S. aureus if compared with lysozyme in solution.

Pd-Fe/SiO2 bimetallic catalysts with a constant amount of Pd and a different Fe/Pd ratio were prepared by sequential wet impregnation and the hydrogenation of 2,4-dinitrotoluene was carried out at 25°C in a batch reactor. The presence of Fe enhances the Pd catalytic activity. The formation of a dispersed Pd-Fe alloy was evidenced through X-ray powder diffraction and is consistent with the data observed by FTIR analysis, TPR, and chemisorption features. The increase of the Fe total content of the catalysts results in the increase of the dispersion of the metallic phase and in the presence of partially oxidized Fe species. FTIR analysis shows that nitrocompounds chemisorb mainly on the support rather than on the metal surface. It is suggested that the Pd-Fe alloy formation is responsible for the increase of the catalytic activity because of a cooperative effect of Fe in the hydrogen transfer step.

Starting from the gel-type, cross-linked copolymer co-poly-{(N,N-dimethethylacrylamide/4-vinylpyridine/N,N′-methylenebisacrylamide} (DV44) we prepared nanoclusters of several noble metals (Ru, Rh, Pd, Pt, Ag, Au) inside its polymer framework through the so-called “template-controlled synthesis” approach. This procedure involves the immobilization of the relevant metal centers inside the polymer framework, followed by their reduction to M0 nanoclusters (in our case, uptake from solutions of suitable precursors and reduction with aqueous solutions of NaBH4, respectively). In this way, a set of monometallic polymer supported nanoclusters (M/DV44, M = Ru, Rh, Pd, Pt, Ag, Au) were obtained. The experimental conditions were set so as to generally obtain a homogeneous radial distribution of the metal throughout the particles of the materials. The latter were characterized by means of transmission electron microscopy for the assessment of the metal nanocluster sizes. The diameter of the nanoclusters generated by reduction inside water-swollen DV44 were compared with the size of the nanopores of the water-swollen polymer framework that had previously been determined by means of inverse steric exclusion chromatography. The diameter of the prevailing pore fractions in water-swollen DV44 was 3.2–4.3 nm and the largest available pores observed had a diameter of 8.1 nm. Nanoclusters with diameters larger than this value were observed in no cases, and in all cases the average diameter of the nanoclusters never exceeded the diameter of the prevailing pore fraction. For Pd/DV44, Ag/DV44 and Au/DV44, the average nanocluster diameter compared very well with the diameter of the prevailing pore fraction.

We investigate the influence of particle size and crystal orientation on the electrochemical behavior of carbon-coated LiFePO4 prepared by a hydrothermal synthesis in the presence of a polymeric surfactant and a source of carbon. We evaluated the charge/discharge profiles of two samples, one constituted by particles in the micrometer range with a platelet-like shape (large ac facet and (020) crystal orientation) and another made of sub-micrometer-rounded particles with a random crystal orientation. At low current rates the crystal orientation seems to be the prevailing factor, whereas at high current rates smaller particles can allow a shorter electronic conduction path, so reducing the resistance experienced by Li ions during diffusion.

At 35 °C, in the presence of supercritical carbon dioxide (80–150 bar) as a solvent, α-olefins (RCHCH2, R = C4–C6) undergo highly selective self-metathesis catalyzed by supported Re-oxide (7%). To the best of our knowledge, this is the first procedure for the metathesis of alkenes, in which heterogeneous catalysts are combined with the use of dense CO2. The intrinsic eco-compatibility and the unique physicochemical properties of this medium offer both environmental and synthetic advantages: not only conventional toxic solvents (e.g. n-heptane and toluene) can be replaced, but the reaction is faster. For instance, after 2 h, the average conversion of 1-octene is 67% and 40% in scCO2 and n-heptane, respectively. The product of self-methatesis, 7-tetradecene, can be isolated in yields up to 68%. At 90 bar, the reaction is rather sensitive to the mole fraction of the olefin (in scCO2); though, the enhancement of the pressure (and the density) of the supercritical medium does not induce significant effects on either the rate or the selectivity of the process. The nature of the catalytic support also greatly affects the reaction outcome: Re-oxide shows good activity if dispersed over γ-Al2O3, while silica-based systems are ineffective.

The effects of gold nanoparticles deposited on titanium dioxide on the photocatalytic oxidative degradation of two organic substrates, i.e. formic acid and the azo dye Acid Red 1, and on the parallel O(2) reduction yielding hydrogen peroxide have been investigated under visible light irradiation. The method employed to reduce Au(iii) to metallic gold in the preparation of Au/TiO(2) photocatalysts was found to affect their photoactivity, also by modifying the properties of TiO(2). The presence of gold on TiO(2) facilitates both the electron transfer to O(2) and the mineralization of formic acid, which mainly proceeds through direct interaction with photoproduced valence band holes. The so-formed highly reductant CO(2)*(-) intermediate species may contribute in maintaining gold in metallic form. The controversial results obtained in the photocatalytic degradation of the dye were rationalised by taking into account that with this substrate, which mainly undergoes oxidation through a hydroxyl radical mediated mechanism, the photogenerated holes may partly oxidise gold nanoparticles, which consequently act as recombination centres of photoproduced charge carriers.

The cross-linked polyurea support EnCat 30, its related macromolecular complex Pd(II)/EnCat 30 and its related Pd(0)/EnCat 30NP nanocomposite are thoroughly investigated with SEM, TEM, ISEC and ESR in the solid state (SEM and TEM) and swollen state in THF (ISEC and ESR). Pd(II)/EnCat 30 and its related Pd(0)/EnCat 30NP are obtained by microencapsulation of palladium acetate in a polyurea framework, which is formed upon hydrolysis/condensation of mixtures of multi-functional oligo-arylisocyanates in dichloroethane. Most remarkably, both Pd(II)/EnCat and Pd(0)/EnCat 30NP turn out to be far more (nano)porous and swellable materials than the blank polyurea matrix (EnCat 30). It is proposed that there is a strong nanostructural effect exerted by Pd(II) species due to its interaction with functional groups (amines stemming from the hydrolysis of the isocyanato groups or ureido groups belonging to the polymer chains) during the growth of the cross-linked polymer framework. As a consequence, the catalytic species in both Pd(II)/EnCat 30 and Pd(0)/EnCat 30NP are much more accessible to molecules diffusing from liquid phases in contact with the materials and, hence, are better catalysts than expected from the morphology of blank polyurea EnCat 30.

The relationship between the catalytic activity and Pd particle size in Pd/ultradispersed diamond catalysts is established in the hydrodechlorination of 1,3,5-trichlorobenzene under multiphase conditions.

We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.

The structural evolution of cobalt nanoclusters synthesized in silica glass by ion implantation has been investigated upon thermal annealing. The samples were characterized by in-situ grazing incidence X-ray diffraction, exploiting a synchrotron radiation beam and following their evolution during thermal treatments in vacuo up to T=800 degrees C. Before heating, the system is composed of hcp Co nanocrystals; we have not detected the transition from hcp to fcc structure that in the bulk phase occurs around 420 degrees C; nevertheless, the differences in the diffraction pattern recorded at T=800 degrees C with respect to the corresponding one at room temperature suggest the presence of a second crystalline phase. (c) 2006 Elsevier B.V. All rights reserved.

Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control deals with the synthesis of metal nanoclusters along all known methodologies. Physical and chemical properties of metal nanoclusters relevant to their applications in chemical processing and materials science are covered thoroughly. Special attention is given to the role of metal nanoclusters size and shape in catalytic processes and catalytic applications relevant to industrial chemical processing. An excellent text for expanding the knowledge on the chemistry and physics of metal nanoclusters. Divided in two parts; Part I deals with general aspects of the matter and Part II has to be considered a useful handbook dealing with the production of metal nanoclusters, especially from their size-control point of view.

In this study, using X-ray diffraction Rietveld analysis, we have determined that a great quantity of very fine particles( < 2 nm) can be present in a supported metal catalyst, but that they are almost undetectable if larger particles (even a very small fraction) are contained in the sample. The large amount of hidden fine particles found in the discussed catalyst convinced us that, probably, such a nanostructure could be characteristic of catalysts containing a low percentage of metal. Since heterogeneous catalysis is a surface phenomenon, it is clear that losing great fractions of nanoparticles biases the microstructural study, and hence, the understanding of the catalytic working mechanism.

Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the preparation parameters, namely, temperature and electric field intensity across the samples. This technique, which allowed to dope the glass matrix with high metal concentration values, can be used as the first step in combined methodologies for the preparation of nanostructured glass composites. The shape of the measured Co diffusion profiles indicates that the migration process depends not only on the experimental parameters but also on the behavior of alkali ions within the glass. Chemical phenomena occurring at the metal/glass interface also play a significant role in the penetration of the Co ions. The possibility of doping the glass with two different metal species was also investigated, with the aim to create the condition for the formation of core-shell or alloy nanoclusters. In particular, preliminary results on Co+Au field-assisted co-diffusion are presented. (c) 2005 Elsevier B.V. All rights reserved.

Silica films containing metal particles in the nanometer size range exhibit optical properties that make them useful in several applications. In this work, copper-containing silica films were synthesized by a radiofrequency magnetron sputtering co-deposition technique, and then thermally-treated (in some cases sequentially) in different annealing atmospheres, i.e. either oxidizing or reducing (700–900 °C of temperature range, 2–5 h of time range, 400 °C/h of heating rate and 250 °C/h of cooling rate). Depending on the thermal treatment, the crystallite average surface-weighted dimension ranges between 5 and 9 nm for metal copper, and is larger than 25 nm for CuO. The preparation protocols to obtain these characteristics were determined in order to control cluster formation and growth. Characterization of the samples following the various preparation steps was performed by Rutherford backscattering spectrometry, optical absorption spectroscopy, and X-ray diffraction. Our experimental observations showed that the composite formation was a function of the annealing conditions.

The liquid phase oxidation of glycerol with oxygen has been studied using a series of monometallic and bimetallic catalysts based on Au, Pd and Pt metals supported on carbon, in order to study the effect of the metal on the distribution of the products. It was found that by using bimetallic catalysts (Au-Pd, Au-Pt) the distribution of the products could be controlled. Moreover, bimetallic catalysts were by far more active than monometallic catalysts. Selectivity could be tuned by using different preparation method. © 2005 Elsevier B.V. All rights reserved.

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.

A new semi-empirical approximation for the asymmetry function to be used in the X-ray Rietveld analysis has resulted in lower values of the so-called goodness-of-fit index, defined as S = Rwp/Rexp, where Rwp is the R-weighted pattern and Rexp is the R-expected [R. A. Young, The Rietveld Method (Oxford U.P., Oxford, 1993)], with respect to the corresponding values obtained with the classical approximation used by Rietveld in his fundamental paper. A comparing test of the two asymmetry functions was carried out for the cubic Y2O3 and for αAl2O3 using either pseudo-Voigt or Pearson VII symmetrical functions and two diffractometers. As in the case of the Rietveld approximation, the present one, which employs an exponential function, is optimized using only one fitting parameter. Experimentally, the asymmetry can be considerably diminished by using Soller slits with a small opening angle (≤2°).

The Al2O3 promotion of ZrO2/SO4 has been shown to influence n-butane isomerization activity. In this paper we report a study of the influence of a small addition of Al2O3 (0.6−10.3 wt %) onto the ZrO2 structure and microstructure. The addition of alumina is related to an increase of the surface area. A detailed X-ray diffraction analysis by the use of the modified Rietveld method allowed us to follow the changes in the crystalline phases and to quantify the amount of amorphous phase. When the Al2O3 content is increased, a decrease of the ZrO2 particle sizes is observed, paralleled by an increase of the amorphous phase. When the Al2O3 content is larger than 3.7 wt %, only amorphous phase can be detected. No crystalline peaks of Al2O3 were ever observed. These data were supported also by TEM and Raman measurements.