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The “ one-pot ” hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180 °C and at relatively low hydrogen pressure of 2 MPa. The impact of metal loading (1–5 wt.%), metal reduction method (H 2 at 350 °C or NaBH 4 ) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose-rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%Pt/AC-SO 3 H catalyst afforded hexitols yield of 69.5 wt.% (at 96.1% conversion) compared to 10.9 wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3 wt.%Ru/AC-SO 3 H, was more favorable for hexitols production (44.5 wt.% yield, at 94.8 wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2–C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (C C cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (≤4 nm, depending on loading) as well as of amorphous oxygen-rich M(O) x δ+ phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1 wt.% Pt or Ru/AC.

We report the structural, electronic and magnetic investigation using extended X-ray absorption fine structure spectroscopy (EXAFS), photoelectron microscopy, spin-resolved photoemission and magneto-optical Kerr effect on the properties of Mn $$_{x}$$ Ge $$_{1-x}$$ systems obtained by molecular beam epitaxy deposition of manganese on Ge(001) wafers annealed on temperatures between 50 and 450 $$^{\circ }$$ C. Magnetic ordering can be achieved when the substrate temperature is higher than 250 $$^{\circ }$$ C, when the manganese tends to diffuse into the Ge matrix and segregate in Mn $$_{5}$$ Ge $$_{3}$$ -like compounds, as proved by EXAFS. High spatial resolution photoelectron spectroscopy reveals Mn inhomogeneities in the 5–10 $$\upmu $$ m range, even though Mn is found mostly in the same chemical state all over the surface.

Samarium is deposited on Si(001) at various temperatures (room temperature to 400 °C), and the surface structure, interface reactivity, electron configuration, and magnetic properties are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and magneto-optical Kerr effect (MOKE), respectively. It is found that metal Sm is present on samples prepared at room temperature with an interface layer containing mostly Sm2+ and a lower amount of Sm3+. When samples are prepared at high temperature, much less Sm0 is found with an increasing amount of Sm2+. Freshly prepared Sm0 and SmSi2 layers react strongly with oxygen from the residual gas, promoting formation of Sm2O3 at the expense of both metal Sm and SmSi2. Room temperature ferromagnetism is observed for all prepared layers with a decrease of the saturation magnetisation when samples are prepared at high temperature. It is found that ferromagnetism implies mostly Sm3+ and Sm metal. In addition to these findings, this work proposes a new assignment of the Sm 3d chemically shifted components. Also, a noticeable variation of the XPS Sm 3d spin-orbit splitting is found as a function of the Sm ionization state.

Cobalt-doped vanadium oxide thin layers prepared by pulsed laser ablation are investigated from the following points of view: (1) the chemical states by X-ray photoelectron spectroscopy (XPS), (2) the local atomic order by X-ray absorption fine structure at both vanadium and cobalt K-edges, (3) the morphology of the films by atomic force microscopy (AFM) and (4) the magnetic properties by magneto-optical Kerr effect (MOKE). The chemical composition of the host matrix was found to be close to VO2 at the sample surface, with V2O3 in the bulk. Co ions are found near the surface in high ionisation states Co4+ (for the samples synthesised in a high vacuum condition, denoted by VO1), or with Co(4− δ )+ (for the samples synthesised in an oxygen atmosphere, denoted by VO2), whereas in the bulk, Co1.5+ is obtained for VO1 and Co2+ is obtained for VO2. The AFM revealed nanoparticles with sizes 10–25 nm for VO1 samples, whereas a few bigger nanoparticles are observed for VO2 samples. The VO1 samples presented high c...

Nitrogen doped TiO 2 aerogels were obtained by sol–gel process followed by supercritical drying with liquid CO 2 . Urea and NH 3 (25% aqueous solution) were used as nitrogen sources. The as-prepared aerogels were submitted to thermal treatments performed under different experimental conditions (temperature and heating time). Increasing the temperature from 450 °C to 550 °C a decrease about 32% and 15.4% of the particle size and surface OH groups’ concentration, respectively and an increase about 21.4% of the incorporated nitrogen in TiO 2 lattice were observed. The immersion of the TiO 2 aerogels in NH 3 solution induced a decreasing by 48.86% and by 80% of the S BET and the aerogel porosity, respectively. The photocatalytic activity of the obtained N-doped TiO 2 was found to depend mainly on the nitrogen incorporation in the TiO 2 lattice.

Unimodal porous system (denoted as SnTf-MCM-41) and bimodal porosity (denoted as SnTf-UVM-7) were prepared in a two-step synthesis. The triflic acid was incorporated into previously synthesized Sn-containing porous silicas. Chemical analysis was carried out by electron probe microanalysis (EPMA), textural properties were determined by transmission electron microscopy (TEM) and from nitrogen adsorption–desorption isotherms (77 K), while structural characterization by X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. The structural characterization provided evidences on the direct interaction of triflate with incorporated tin species. The acidity of these catalysts was determined from the ammonia chemisorption measurements. The catalysts have been tested for transesterification of sunflower oil under both microwave and ultrasound activation. These experiments showed a direct reaction between the acidity of the catalysts and catalytic performances. No leaching of the triflate species or catalyst deactivation have been detected over several runs.

Iron- and europium-doped (≤1 at.%) TiO 2 nanoparticles powders have been synthesized by a hydrothermal route at 200 °C, starting with TiCl 4 , FeCl 3 ·6H 2 O and EuCl 3 ·6H 2 O. The structure, morphology and optical peculiarities were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), Mossbauer spectroscopy and UV–vis measurements. The photocatalytic performance was analysed in the photodegradation reaction of phenol. Rietveld refinements of XRD patterns reveal that the as-prepared samples consist in iron- and europium-doped TiO 2 in the tetragonal anatase structural shape, with particle size as low as 15 nm. By means of Mossbauer spectroscopy on both 57 Fe and 151 Eu isotopes as well as by EXAFS analyses, the presence of Fe 3+ and/or Eu 3+ ions in the nanosized powders has been evidenced. It was found that iron and europium ions can substitute for titanium in the anatase structure. From the UV–vis reflection spectra, by using the transformed Kubelka–Munk functions, the band gap energy ( E g ) of the hydrothermal samples has been determined in comparison with that of Degussa P-25 photocatalyst. A decrease of E g from 2.9 eV found for Degussa photocatalyst to 2.8 eV for the titania doped with 1 at.% Fe has been evidenced, indicating a valuable absorption shift (∼20 nm) towards visible light region. However, the best photocatalytic activity in the photodegradation reaction of phenol was evidenced for the hydrothermal sample, TiO 2 : 1 at.% Fe, 0.5 at.% Eu, in both UV and visible light regions. The photocatalytic activities of iron-doped and iron–europium-codoped samples are high and practically the same only in visible light. The photocatalytic properties in correlation with the structural and optical peculiarities of the hydrothermal samples are discussed.

Carbon layers grown on lead zirco-titanate (PZT) weakly interact with the substrate and exhibit a nearly two dimensional character, up to a carbon surface density approaching that of graphene. The first feature is evidenced by X-ray photoelectron spectroscopy, and the second by angle resolved near-edge-absorption spectroscopy (NEXAFS). The binding energies and lineshape parameters of C 1s are similar to that of graphene. The dichroism of C K-edge NEXAFS shows the prevalence of in-plane sp2 bonds for layers whose effective coverage is below the graphene surface density. The polarization state of the substrate, oriented outwards, is preserved upon carbon deposition. The surface Pb content is strongly affected by the carbon ad-layers.

The influence of the Mn, Se and Sb impurities on the structure and morphology of CdS thin films grown on p + Si wafers was studied. The starting powders were mixed in the same molar ratios (0.3%) and deposited in the same conditions by vacuum thermal evaporation. X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and reflectance studies made on thermal treated thin films (573 K, 2 h in air) evidenced that thin films have a hexagonal oriented structure, and that dopants enter into the CdS lattice merely by substitution. The dopant nature influences the thin film thickness and chemical composition. The doped CdS thin films have roughness in nanometer region and a reflectivity lower than 40%. Silicon substrate acts as a template and favors the retention of Mn and scatters the Sb dopants. The CdS:Se thin film is thicker than CdS:Mn and CdS:Sb ones and is a mixture of doped and undoped nanocrystals.

Results are reported on the characterization of 200–250 nm thick TiO x transparent films grown at temperatures of 150 °C and 500 °C by reactive pulsed-laser ablation of a metallic Ti target under 0.13–13.3 Pa oxygen atmosphere. Film structure and composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The samples deposited at 150 °C reveal a mixture of amorphous TiO 2 and Ti 2 O 3 , irrespective of oxygen pressure. The O:Ti atomic ratio fluctuates in their surface around 1.83 for oxygen pressure ranging between 0.13 Pa and 2.66 Pa. The samples deposited at 500 °C feature different characteristics, as a function of oxygen pressure: (a) below 2.66 Pa of O 2 the films contain a mixture of significant amount of anatase and rutile TiO 2 phases, along with titanium suboxides; (b) above this threshold, the rutile phase vanishes, the anatase TiO 2 phase remaining dominant along with small amounts of nanocrystalline suboxides. The size of the anatase nanocrystallites decreases with the increase of oxygen pressures. The samples deposited at 500 °C feature a slight improvement of surface stoichiometry, from roughly TiO 1.8 to TiO 1.9 . The films deposited at high substrate temperature and oxygen pressure are highly hydrophilic.

The substitution of up to 7 at. % of gold into icosahedral Al62Cu25.5Fe12.5 quasicrystals has been investigated by 197Au and 57Fe Mossbauer spectroscopy. Gold was found to replace copper on BC1 sites and to hybridise strongly with its Al neighbours. In addition, particularly at the higher gold concentrations, the precipitation of small amounts of AuAl2 and β-FeAl was observed.

Ru-zeolites prepared via deposition of aqueous solution of ruthenium chloride on X, L, ZSM-5 and APO-54 were investigated. The impregnated solids were characterized by the following techniques: N-2 sorption, H-2 chemisorption, TPR, XRD, XPS, EXAFS and Mossbauer spectroscopy. It was found that deposition of Ru is influenced by the pore structure and the chemical composition of the supports, in particular the concentration and strength of the protonic sites, with the formation of the different species. The packing of Ru as well as the degree of the reduction and the metal particle size are different according to the penetration depth of the metal and the nature of the zeolite. The amount of chlorine possibly remaining as adatoms of Ru is very low or inexistent. In calcined and reduced catalysts no chloride peak could be evidenced by XPS. The experiments confirmed that the use of large amounts of Ru chloride precursor leads to rather large metal particles. (C) 1999 Elsevier Science B.V. All rights reserved.

A sweet catalyst: A catalyst formed of Ru/functionalized silica-coated magnetite nanoparticles is highly efficient in the one-pot production of sorbitol and glycerol, starting from cellulose and in the absence of an external hydrogen source. The ease of recoverability of the catalyst from the solid residues, and its reuse without loss of activity or selectivity for several runs, is an important green element of the process.

Cobalt environment and magnetic defects nature in hydrothermal synthesized anatase CoxTi1−xO2 nanopowders (0 ≤ x ≤ 0.1) are investigated by x-ray diffraction and a variety of spectroscopic techniques. One shows that cobalt is partially inserted in the anatase lattice, as Co2+ ions located on substitutional and interstitial sites. The fraction of the diluted Co is limited to 3 at. % for x ≥ 0.05, while the rest of the Co atoms gather into Co3O4 clusters. As found by electron paramagnetic resonance, the Co doping brings about hole- and electron-excess defects.

Silicalite embedded BiOx clusters were prepared both with and without Na using sodium silicate and tetraethylorthosilicate as silicium precursors. Catalysts with 3 and 5 wt% Bi were obtained. The MFI structure was established from XRD, TEM, and N2 adsorption measurements. No deterioration of the silicalite framework by bismuth was observed. Bi exists as BiOx clusters as evidenced from XPS and EXAFS characterization. These clusters are localized inside the silicalite channels. Py-FTIR measurements indicated that 5wt% Bi led to the formation of strong Lewis acid sites. Epoxidation of cyclohexene was found to depend on both Bi and Na content. On 3%Bi-ZSM-5 it occurred with rather good conversion and selectivity to epoxide. No visible leaching was evidenced. The catalysts were reused for several runs.

Pd-Ln/γ-Al 2 O 3 (Ln-Sm, Gd, Dy, Ho, Tm) catalysts containing 0.1%Pd- 1%Ln, 0.3%Pd -1% Ln and respectively, 0.5% Pd -1% Ln (percentage in wt.%) were investigated. Introduction of Ln leads to an increase of the vinylbenzenes conversion comparatively with monometallic Pd/γ-Al 2 O 3 catalysts. The turnover frequency (TOF) calculus of the latter catalysts suggests that there are no difference among these. In the case of bicomponent Pd-Ln/γ-Al 2 O 3 catalysts, if one considers that the reaction occurs only on the palladium particles, then introduction of Ln seems to increase the TOF and vinylbenzenes hydrogenation seems to be, controlled by the mass transfer processes as indicated by the Koros-Nowak criterion. However, by taking Ln into consideration when calculate the TOF, it results that bicomponent catalysts behave like those monocomponent and the slope of the Koros-Novak dependence is included in a range typical for kinetically controlled reactions. This behavior could be associated to direct participation of Ln to reaction using hydrogen spilled over from the palladium particles.

Preparation of modified ruthenium molecular sieves has been investigated in two steps-depositionof ruthenium and modifying of ruthenium molecular sieves in presence of ligands. As support sieve there were used two molecular sieves with large pore apertures and low acidity strength (zeolite L and APO-34). Correlation of in situ UV-VIS ruthenium deposition measurements with catalyst characterisation revealed that ruthenium deposition takes place not only through ionic exchange but also through adsorption of ruthenium hydrolysed species. Modifying of the ruthenium molecular sieves catalysts with ligands has as effect a diminution of electronic charge on metal. The experimental data indicate that the presence of ligand favours an enantioselective hydrogenation of D-fructose to D-mannitol even if the yields are not very high.

Real regenerated supported palladium (0.5wt.%Pd-LiAl5O8) catalysts used in the hydrogenation of alkenes or alkynes and alkadienes were sintered at high temperatures (300, 500 or 600 °C) in a hydrogen atmosphere, and subjected to alternative treatments in either reducing and/or oxidizing atmospheres. X-ray diffraction analysis indicated hydride formation in the reducing stage, with intermediate compositions ranging between α-PdH and β-PdH, while on using the extended X-ray absorption fine structure technique palladium oxide was observed in catalysts subjected to oxidizing conditions. The statistics of the palladium-crystallite size distributions, as obtained by transmission electron microscopy, showed evidence of sintering and/or redispersion (splitting), as a result of the alternative reducing or oxidizing treatments. The catalytic activity in the alkadiene hydrogenation reaction is influenced by the treatment sequence applied to the regenerated catalysts.

The results of a combined study using diffuse reflectance spectra, temperature-programmed reduction, and extended X-ray absorption-edge fine structure of chlorine-containing precursors formed during preparation of Pd/Al 2 O 3 catalysts are reported. The catalyst dried (385 K) after impregnation contains both PdCl 4 2- species adsorbed electrostatically (about 60-70%) and strongly interacted PdCl x O y species. Calcination at 775 and 925 K results in decomposition of the initial impregnated species, formation of highly distorted PdCl x O y structures, and nucleation of disordered PdO clusters. Growth of large PdO particles occurs during calcination at 1075 K. The reduction of the oxide phase is more facile than that of chlorinated species in intimate interaction with alumina. The concept of geometrical constraints during adsorption of square planar PdCl 4 2- species on various configurations of positively charged hydroxyl groups on different crystal planes of alumina is discussed. It is proposed that electrostatic adsorption is favored on (100) and (110) planes, where the adsorbate matches the configuration of oppositely charged surface sites. The misfit between adsorbed species and surface hydroxyls on the (111) planes leads to ligand-substituted species.