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Coronary artery vasospasm is typically managed through avoidance of triggers and with symptomatic treatments with calcium channel blockers and long-acting nitrates. Here, we report a rare case of medically refractory coronary artery vasospasm associated with genetic predispositions that initially required cardiac autotransplantation followed paradoxically by nicotine for long-term symptomatic control. (Level of Difficulty: Intermediate.), Central Illustration

International audience; The concept of interfacial coordination chemistry was one of the innovation for which Michel Che became internationally known during his tenure as full professor at the Université Pierre et Marie Curie. Isolated metal ions on oxide surfaces behave like coordination compounds to which the surface contributes not only via neutral oxo bridges but also via hydroxyl groups. The latter being pH sensitive, the surface can be charged either positively or negatively, allowing selective adsorption of transition metal ions of opposite charge. In the early eighties, examples exploiting these properties for the preparation of oxide/metal supported catalysts were still rare. This review presents Michel Che's early studies, mostly on molybdenum and nickel ions, on which he built, developed and promoted the concept of interfacial coordination chemistry, now widely used in the field of heterogeneous catalysis. This allowed him and his close collaborators to achieve a molecular-scale understanding of several catalyst preparation procedures, such as impregnation, selective adsorption, grafting, depositionprecipitation, and zeolite functionalization. The impact and legacy of the concept of Interfacial Coordination Chemistry on the current design of improved catalytic formulations is also reviewed.

Cigarette smoking is undoubtedly the single most important risk factor and trigger for vasospastic angina, a condition also known as Prinzmetal angina secondary to coronary artery vasospasm. Even decades before vasospastic angina was first described by Dr. Myron Prinzmetal and his colleagues in 1959, there had been suspected connections between smoking and coronary artery vasospasm in what was alluded to then as "tobacco angina." The intimate relationship between smoking and vasospastic angina has since been extensively researched and validated through decades of epidemiological and clinical studies. The fact that smoking would aggravate vasospastic angina comes with very little surprise, as it has been shown to adversely impact many of the disease processes thought to underlie vasospastic angina, including autonomic dysfunction, endothelial dysfunction, smooth muscle hyperactivity, and genetic susceptibility. While avoidance of smoking is the first logical step in managing smokers with vasospastic angina, there have been reported cases of vasospastic angina paradoxically triggered by smoking cessation or relieved with smoking resumption or nicotine replacement therapy. Thus, there appears to be patient-specific factors that could significantly alter the close connection between smoking and vasospastic angina, warranting further mechanistic investigations. In this review, we will examine this complicated relationship between smoking and vasospastic angina from multiple perspectives (historical, mechanistic, and clinical) and call attention to the "smoking paradox," which, with further elucidation, may provide additional insight into the complex mechanisms of VSA and potentially new strategies to treat medically refractory VSA, at least in selected individuals.

International audience; A monometallic Ni and a bimetallic Ni-Fe catalyst were used in the aqueous phase hydrogenation of xylose in batch conditions (T = 50–150 °C, PH2 = 10–30 bar, xylose mass fraction in water = 3.7–11.0 wt.%) to evidence the benefits of promoting Ni by Fe. The activity of the catalysts increased with temperature, but a temperature of 80 °C allowed minimizing nickel leaching at full conversion. The presence of reduced Fe at the surface of the bimetallic nanoparticles increased both the first-order apparent rate constant and the adsorption constant of xylose. The catalytic activity of Ni/SiO2 strongly declined and no deactivation was found for the Ni-Fe catalyst. A restructuring of the bimetallic nanoparticles took place, as the size of the metal particles and the Fe proportion in the surface layers increased, suggesting a flattening and coalescing of the particles over the silica surface.

International audience; Copper is active in hydrogenation reactions, but it is a base metal difficult to disperse inside mesostructured supports, with adverse consequences on the catalytic properties. Incorporating aluminium into mesoporous SBA-15 silicas allows solving both problems of Cu dispersion and activity. The incorporation of 20 wt.% Al2O3 in the SBA-15 host structure leads to an increase of the copper metallic surface area by a factor 6 compared to the pure siliceous SBA-15-supported catalyst. The support also proves to be stable upon exposure to the impregnation aqueous solution used for copper introduction. The incorporation of Al provides Lewis acidic sites that favour the transformation of cinnamaldehyde into cinnamyl alcohol, a feature usually assigned to larger metal particles. As a consequence, the catalytic activity of Cu catalysts is enhanced compared to silica-supported Cu catalysts, while the chemoselectivity towards the unsaturated alcohol appears to be similar to that of a mesoporous alumina-supported system.

The selective hydroconversion of 5‐hydroxymethylfurfural (HMF) to biofuels is currently highly sought‐for. While the literature has demonstrated that this reaction is possible on promoted Ni catalysts, we show here that a monometallic, non‐promoted Ni/SBA‐15 catalyst, prepared by incipient wetness impregnation, can convert HMF to 2,5‐dimethylfuran (DMF) and to 2,5‐dimethyltetrahydrofuran (DMTHF) at 180 °C, in a consecutive way. Through a control over reaction time, high yields to DMF (71 %, at conversion of 93 %) or DMTHF (97 %, at conversion of 100 %) can be achieved. Kinetic modelling suggests a preferential route to DMF via 5‐methylfurfural (MFFR) as intermediate, though the route via 2,5‐bis(hydroxylmethyl)furan (BHMF) is also present. The favored route in the experimental conditions involves the hydrogenolysis of the hydroxyl group of HMF as first step, followed by the hydrogenation of the aldehyde function, to methylfurfuryl alcohol (MFOL). It is suggested a higher reaction rate of hydrogenation or hydrogenolysis of the side group is linked to the presence of a methyl group in the molecule. No hydrogenation of the furan ring is detected on the intermediates. 12;7

The inert gas condensation method (IGC) produces multimetallic nanoparticles in a metastable state that may exhibit heterogeneities of size, structure, and composition. The deposition of IGC-fabricated nanoparticles on substrates allows for a detailed characterization by combination of aberration-corrected scanning transmission electron microscopy (TEM) and atom probe tomography (APT). Multiple particle monitoring and high-resolution scanning TEM give access to the size distribution of Au-Cu nanoparticles (h structure for smaller particles (7 nm), while Cu is more randomly distributed in smaller particles.

International audience; Supported Fe-Ni catalysts have been reported for their activity and selectivity in the hydrogenation of unsaturated organic molecules. However, the control of the size and composition of the bimetallic nanoparticles remains a bottleneck when oxide-supported catalysts are prepared by impregnation, and alternative procedures should be investigated. Starting with Ni(II) and Fe(II) sulfates as precursor salts, deposition-precipitation with urea (DPU) on SiO2 in an inert atmosphere initially leads to the formation of an ill-crystallized Fe-containing Ni(II) 1:1 phyllosilicate, which reduces under hydrogen at 700 °C into bimetallic fcc Fe-Ni nanoparticles of 5.4 nm in average. Compared with the composition of the DPU solution (50 Fe at %, 50 Ni at %), an excess of Ni is detected on the catalyst (38 Fe at %, 62 Ni at %), due to the preferential reaction of Ni2+ ions with silica. In situ X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy show that the reduction of Fe ions to the metallic state is triggered by the formation of reduced Ni centers above 350 °C, and, from then, proceeds progressively, resulting in an excess of Fe in the outer shells of the bimetallic particles. The composition of individual Fe-Ni particles evidences a standard deviation of 8%. The bimetallic Fe-Ni/SiO2 catalyst gives high yields in furfuryl alcohol in the hydrogenation of furfural, in contrast with an analog Ni/SiO2 catalyst that favours side-reactions of etherification, hydrogenolysis and hydrogenation of the furan ring.

Metallic nickel is known to efficiently catalyze hydrogenation reactions, but one of its major drawbacks lies in its lack of selectivity, linked to side-reactions of hydrogenolysis and over-hydrogenation. More selective hydrogenations can be obtained upon the introduction of a second metal in combination with Ni. Fe is an interesting choice, as it is a cheap and abundant metal. This review aims at discussing the advantages and constraints brought by the preparation procedures of bimetallic supported Ni–Fe nanoparticles, and at analyzing the benefits one can draw by substituting Ni–Fe supported catalysts for Ni monometallic systems for the catalytic hydrogenation of organic molecules. Specific formulations, such as Ni75Fe25, will be singled out for their high activity or selectivity, and the various hypotheses behind the roles played by Fe will be summarized.

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Understanding how alumina degradation to boehmite AlOOH can be prevented under hydrothermal conditions is key to design more stable catalysts supported on alumina for Fischer–Tropsch synthesis. We compare the effect of four inorganic dopants to inhibit γ-alumina chemical weathering under hydrothermal conditions: three metal ions: Mg2+, Zr4+, Ni2+, introduced by impregnation, and nonmetal Si, introduced by the grafting of tetraethyl orthosilicate. Boehmite is formed by a mechanism of dissolution–precipitation. A significant decrease of alumina weathering to boehmite is evidenced for all dopants. For metal ions, the thermal conversion of doped γ-Al2O3 into an alumina-rich mixed oxide or the coverage of the alumina surface by particles of a poorly soluble oxide such as NiO contribute to the stabilization of the solid. Alumina dissolution and degradation are only inhibited fully through Si grafting. IR spectra in the OH stretching region suggest that the most reactive alumina sites toward dissolution are basic Al−OH sites located on lateral facets that are blocked upon Si introduction. Fischer–Tropsch reactivity shows that Co catalysts prepared on Mg2+- and Si-doped supports are less active or, at best, as active as a reference Co/γ-Al2O3 catalyst, which is explained by a lower reducibility of CoO on doped supports. The Co catalyst prepared on Mg2+-doped γ-Al2O3 calcined at 900 °C exhibits the best combination of catalytic activity, ease of preparation, and hydrothermal stability.

International audience

Copper (oxide) nanoparticles with dispersion and size ranging from highly dispersed nanoparticles confined within the intra-wall pores to nanoparticles confined within the main mesopores can be simply produced via incipient wetness impregnation by using mesoporous silica supports containing the structure directing agent P123 partially occluding the intra-wall pores of SBA-15. Remarkably high copper dispersions of 69.5 down to 25.9% for metal loadings from 5 to 20 wt% were achieved as a result of the dual effect of the presence of surface silanol groups and the unique confining space between the silica walls and residual P123 in the intra-wall pores. The copper catalysts demonstrated outstanding activities in the hydrogenation of cinnamaldehyde, with TOF values ranging from 5.1 × 10−3 to 22.1 × 10−3 s−1, which are much higher than those of other supported copper catalysts reported elsewhere and prepared using conventional approaches.

International audience; Alcohol dehydration is of prominent relevancein the context of biomass conversion. This reaction can beefficiently catalyzed by alumina surfaces, but the nature ofactive sites, the mechanisms involved, and the key parametersto tune both the activity and the alkene/ether selectivityremain a matter of debate. In the present paper, isopropanoldehydration to propene and diisopropylether over γ-alumina,δ-alumina, and sodium-poisoned γ-alumina was investigatedthrough a combined experimental and theoretical study. Theexperimental kinetic study shows that dehydration occursfollowing the same reaction mechanism on all materials, although γ-alumina activated above 450 °C exhibits the highest densityof active sites and the highest global activity. Results suggest that all the reaction pathways involved in dehydration require thesame set of adjacent active sites located on the (100) facets of γ-alumina. DFT transition-state calculations of the formation ofpropene and diisopropylether on the main terminations of alumina, (110) and (100), were also performed. The less activatedpathways for both the formation of the olefin (E2 mechanism) and the formation of the ether (SN2 mechanism) were found on aAlV Lewis acidic site of the (100) termination, with calculated activation enthalpies (125 and 112 kJ·mol−1 for propene anddiisopropylether formation, respectively) in good agreement with the experimental values (128 and 118 kJ·mol−1, respectively).The higher or lesser selectivity toward propene or ether appears to originate from significantly different activation entropies. Theeffect of coadsorbed sodium on the reaction is linked to the poisoning of Al sites by neighboring, Na-stabilized OH groups, butno influence of sodium on distant sites is evidenced. Reaction temperature is identified as the main key parameter to tune alkene/ether selectivity rather than morphology effects, which in turn affect drastically the number of available active sites, and thuscatalytic activity.

International audience; Amphiphilic organo-polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50-100 nm polystyrene-POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM-mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.

International audience; Complete reduction of the metal phase in cobalt-containing catalysts is often difficult to reach and can be promoted by a small amount of noble metals. Because these costly promoters are introduced in a very low quantity, their speciation and their chemical interaction with cobalt have seldom been studied in detail. We present here a time-resolved in situ X-ray absorption spectroscopy investigation of the speciation of ruthenium, used as a reduction promoter of cobalt, throughout the preparation of Co/SiO2 catalysts. In the cobalt(II) nitrate impregnation solution, ruthenium is detected as hydrated Ru(OH)4 short-chain oligomers that are deposited on silica upon drying. Co3O4 forms during calcination in air and catalyzes the elimination in the gas phase of 60% of Ru. The addition of a polyol, sorbitol, in the impregnation solution stabilizes the whole of Ru on the catalyst. Upon calcination, Ru(IV) ions are inserted inside Co3O4 nanoparticles. Reduction of the oxidic phase takes place in two distinct steps, at approximately the same temperatures regardless of the ruthenium content: first to Ru(III)-containing CoO nanoparticles (Ru ions modifying the intrinsic electronic properties of the oxidic nanoparticles); then to bimetallic Co nanoparticles containing Ru(0) atoms, via an autocatalytic process. Ru loadings as low as 0.2 wt % are sufficient to afford complete reduction of cobalt. Close association between Ru and Co from the beginning of the synthesis is thus necessary for a maximum promoting effect

International audience; Platinum gauze catalysts are used extensively in the production of nitricacid from ammonia, where they are subject to harsh operating conditions combiningelevated temperatures and oxidizing environments. These cause significant loss of metalspecies as volatile oxides. How different metallic species behave in these environments ata fundamental, atomic-scale level is not well understood. In this work, we study the earlystages of oxidation of a Pt−Rh−Pd gauze at temperatures of 873−1273 K. Using acombination of advanced experimental methods, we explore how the oxidation behaviorcan strongly influence the surface and near-surface gauze microstructure. We show thatRh and Pd can segregate on different areas of the same surface and discuss how suchatomic migration can be linked to mechanisms of metal loss from such alloys.

International audience; tThe introduction of organic additives, such as polyols, sugars or polyacids, in impregnation solutionshas been suggested to better control the size of nanoparticles on supported catalysts. The present paperfocuses on the roles played by three of these additives, sorbitol, glucose and citric acid, in the preparationof Ni/Al2O3catalysts. ATR-IR, circular dichroism spectroscopy and viscosity measurements show thatthe additives act as modifiers of the physical properties of the solutions, by increasing their viscosity viahydrogen bonding, rather than as stable ligands toward Ni2+ions. Recrystallization of the nickel precursorsalt is prevented upon drying. As a consequence, no population of large particles is evidenced by XRDand TPR on the catalysts prepared with additives, unlike reference catalysts prepared by conventionalimpregnation of nickel nitrate. Adding these organic molecules in the impregnation solution is thusan easy way to narrow the size distribution of NiO nanoparticles without significantly affecting theirreducibility.

International audience; A molecular-scale investigation of the interaction at room temperature between gaseous trichlorosilane (HSiCl3), used as a passivating agent, and surfaces of aluminum alloy AA6061 in a polished or hydroxylated state is conducted. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) provide information on the topography and morphology of AA6061 before and after hydroxylation and surface passivation, while surface chemistry has been investigated by Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Oxidation and hydroxylation of the polished alloy surface in boiling water strongly modifies the roughness of the surface, with formation of platelets and needles of oxyhydroxide AlOOH. PM-IRRAS and XPS reveal that, upon adsorption, HSiCl3 dissociates and mainly forms HSiOHn(OAl)3−n, HSi(OSi)n(OAl)3−n and condensed HSiOx species, by reaction with single bondOH groups from the AlOOH surface phase. The amount of deposited Si-containing species is larger on the rough surface of the hydroxylated alloy and this deposit is accompanied by a decrease of the amount of free single bondOH groups evidenced by PM-IRRAS. These results can find applications in the field of functionalization of aluminum alloys. It is suggested that a homogeneous oxidation of the alloy surface prior to exposure to gaseous HSiCl3 may enhance the adsorption of the passivating agent.

International audience; Temperature-programmed reduction (TPR) profiles recorded on calcined Ni/Al2O3 catalysts exhibiting the same Ni(II) surface density (3 Ni2+ nm−2) suggest that nickel speciation and reducibility are significantly influenced by the specific surface area and texturalproperties of aluminas, and by their stability toward water during impregnation. Limiting the dissolution of Al2O3 and protecting Ni2+ ions are required to increase the reducibility of Ni/Al2O3 catalysts, especially for mesoporous aluminas presenting a high specific surface area.

International audience

International audience; The paper focuses on the impact of sorbitol addition on the genesis of cobalt active phases in silica-supported catalysts and on their performance in Fischer-Tropsch synthesis. The catalysts were characterized by ex situ and in situ diffuse reflectance spectroscopy in the ultraviolet and visible regions, differential thermal and thermogravimetric analyses combined with mass spectroscopy, in situ Quick-X-ray absorption, X-ray diffraction, H2-temperature programmed reduction, in situ magnetic measurements and propene chemisorption. Sorbitol retards the decomposition of cobalt ionic complexes into Co3O4 during thermal treatment in air, leading to higher cobalt oxide dispersion. The smaller cobalt oxide particles in sorbitol-derived samples exhibit a much lower reducibility than those prepared without the additive. Fischer-Tropsch reaction rate is proportional to the number of cobalt metal sites, which is a function of both cobalt dispersion and cobalt reducibility. It depends in a complex manner on the initial sorbitol content.

Three Pt catalysts exhibiting similar metal particles size ( C bond was favored with Pt/SBA-15 and Pt/Al-SBA-15, with significantly higher reaction rates on the latter catalyst. The acidic support changes the adsorptive properties of the platinum nanoparticles, modifying their surface electron density and possibly their morphology. In contrast, Pt/Al2O3 was the most selective catalyst of the series toward cinnamyl alcohol, with C C and C O hydrogenations taking place at the same rate. The presence of Lewis acidic sites close to the particles is assumed to favor the adsorption of molecules via their polar C O bond. Even if cinnamaldehyde hydrogenation does not require acidic sites to be performed, the composition and acidity of the support significantly influence the reaction rate and selectivity.

67-1 FIELD Section Title:Catalysis, Reaction Kinetics, and Inorganic Reaction Mechanisms 66 Laboratoire de Reactivite de Surface (UMR 7197 CNRS), Universite Pierre et Marie Curie, Paris, Fr. FIELD URL: written in English; Nickel(II) nitrate is the nickel precursor generally selected to prep. oxide-supported catalysts, due to its low cost, high soly. in water and decompn. at moderate temps. However, its decompn. produces NOx, and it is known to melt and redistribute over the support upon heating, leading to poorly dispersed metal particles after redn. and to their partial expulsion from the porous support system. The benefits of using NiII acetate as an alternative to NiII nitrate are explored by investigating a series of model Ni catalysts (1-5 wt %) prepd. from the mesoporous siliceous supports MCM-41 and Al-MCM-41. The problems encountered with NiII nitrate, in terms of particle size and redistribution of nickel, are not obsd. with NiII acetate. In the case of MCM-41-supported systems, metal particles are well dispersed and remain located within the porous support. The higher pH of the impregnation soln., favoring electrostatic interactions between nickel ions and the support, may account for the higher metal dispersion. The formation of silicate-like species in strong interaction with the support does not appear prominent on siliceous MCM-41 when nickel acetate is the precursor, but seems to be enhanced for higher Ni contents. Finally, Al-MCM-41 supports are more sensitive to the exposure to nickel acetate than their siliceous analogs because acetate ions are able to ext. Al ions from the support, resulting in a partial disruption of the support organization and to the formation of nickel silicate species. [on SciFinder(R)]

52-1 FIELD Section Title:Electrochemical, Radiational, and Thermal Energy Technology 67 Laboratoire des Materiaux, Surfaces et Procedes pour la Catalyse (UMR 7515 CNRS), Universite de Strasbourg, Strasbourg, Fr. FIELD URL: written in English; Isooctane reforming under conditions which are set by exhaust gas can be used to generate H on-board. Isooctane reforming reactivity tests have been performed with bimetallic catalysts Co-noble metal/ceria-zirconia, prepd. either by insertion of transition metal in a ceria-zirconia matrix, either by their impregnation on ceria-zirconia. The influence of the prepn. procedure on the activity of the noble metal-doped catalysts is discussed. [on SciFinder(R)]

New heterogeneous catalysts for alkene metathesis were prepared by immobilization of molybdenum dioxide bis(acetylacetonate) and molybdenum dioxide bis(glycolate) on mesoporous molecular sieve SBA-15. Thermal spreading (TS) method and wet impregnation (WI) followed by calcinations were employed as synthesis approaches. These new catalysts represent inexpensive, easy-to-prepare and highly active and selective heterogeneous catalysts for metathesis of higher linear 1-alkenes applicable under mild reaction conditions without the necessity of solvent or co-catalyst in the reaction mixture. In metathesis of 1-octene, these catalysts showed up to four times higher activity compared with MoO 3 supported on conventional silica as well as on SBA-15. This is probably due to the better dispersion of the molybdenum oxide phase on the mesoporous support surface. In metathesis of 1-dodecene and 1-tetradecene these catalysts based on SBA-15 exhibited a significantly higher activity than corresponding catalysts on MCM-41, probably due to the larger pores.

Differences between the acidic properties of silicoaluminic Pt-containing catalysts and those assessed on their parent supports have been reported in the literature and attributed to the presence of the metal nanoparticles and to their influence on the acid sites. It is shown here that for mesoporous materials containing various types of Al species, an alternative explanation can be proposed. 27Al NMR spectroscopy, FTIR of adsorbed CO and probe catalytic tests suggest the redistribution of aluminium atoms upon contact of the parent support with the aqueous solution containing the Pt precursor. Upon contact with water and thermal treatment, strong and mild Bronsted sites (Si–O(H)–Al) transform into strong Lewis sites (isolated tetracoordinated Al atoms). As a consequence, it may not be straightforward to deduce the acidic properties of metal-containing catalysts supported on Al-containing mesoporous materials from those of the bare support, because the surface species may differ significantly.

In the present work, nanocatalysts prepared on inorganic supports (zeolites) were investigated in d-glucose oxidation and compared to systems supported on polymer (hypercrosslinked polystyrene (HPS)) previously described. Catalytic activities and selectivities were measured under various reaction conditions. The selectivity of d-glucose oxidation and activity of both Pd-containing zeolites and HPS-Ru were similar (99.7% and TOF 0.013–0.014 mol/(mol Me s)). Physicochemical analysis X-ray photoelectron spectroscopy, liquid nitrogen physisorption, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO for metal sites evaluation, CD3CN for acid sites evaluation showed that Pd species were in oxidic form, while Ru species were in oxidic and reduced form. The catalytic activity decreased when acidic sites were present in Pd-containing zeolites.

International audience; EXAFS spectroscopy is shown as a tool of prime importance to probe the formation of metal–oxygen–support bonds and unravel the surface molecular structure in oxide-supported systems through two examples: (i) a molecular metal complex (Ni(II) bisglycinate) characterized after impregnation and drying on Al2O3, and (ii) a tungsten oxide nanophase characterized after deposition on zirconia and high temperature thermal treatment (tungstated zirconia catalysts, i.e. WOx/ZrO2). Unlike other spectroscopic techniques, EXAFS at the Ni K-edge proves that a modest thermal activation during the impregnation step triggers the grafting of nickel(II) bisglycinate onto the support: Al next-nearest neighbours are detected when the impregnation is carried out at 60 °C instead of room temperature. Characterization of WOx/ZrO2 catalysts shows the presence of W next-nearest neighbours around tungsten, with W–W distances distinctive of edge-shared WO6 octahedra only. The WOx overlayer can thus be described as bidimensional, nanometric slabs of 4 to 5 WO6 units on each side. In these slabs, W octahedra are interconnected to form a more condensed structure than the one present in bulk WO3 (in which linkage through corners exists). Moreover, EXAFS results conclusively demonstrate that the WOx overlayer is directly anchored to the ZrO2 surface by means of W–O–Zr bonds with a W–Zr distance of 3.14 Å.

Environmental context. The wide use of pesticides for pest and weed control contributes to their presence in underground and surface waters, which has led to a continuously growing interest in their environmental fate. Soils play a key role in the transfer of these compounds from the sprayer to the water as a result of their capacity to retain pesticides depending on the soil components. The knowledge of soil composition should enable one to predict pesticide behaviour in the environment. Abstract. Eight calcareous soils of Champagne vineyards (France) were studied to investigate the adsorption of the herbicide terbumeton (TER). A preliminary characterisation of the soil samples using X-ray diffraction (XRD), elemental and textural analyses, revealed a wide range of soil properties for the selected samples. The adsorption isotherms of TER were plotted for all samples. The determination of soil properties, which significantly correlated with the Kd distribution coefficient, allowed identification of organic matter and CaCO3 as the two main soil components that govern the retention of the herbicide. Organic matter was the predominant phase involved in the retention but its role was limited by the presence of calcite. Finally, the ratio of CaCO3 content to organic matter content was proposed as a useful parameter to predict the adsorption of terbumeton in chalky soils. The evolution of Kd as a function of this ratio was successfully described using an empirical model.

In the present paper are compared the physicochemical properties and stability of mesoporous aluminas synthesized following five routes in which water is the solvent. TEM shows that high pHs lead to heterogeneous materials because of the initial formation of bayerite, which is converted to η-alumina upon calcination and may reappear upon contacting the calcined oxide with water. The most promising procedures use neutral organic additives at moderate pH; materials are homogeneous, with specific surface areas of 350 ± 20 m2 g−1. The similarity of results obtained for the different routes, whatever the organic additive, suggests that the formation of the precipitated phase occurs not around micelles, but through the formation and sticking of boehmite nanoparticles, mediated by the organic agent present in a molecular form or as aggregates. The different ways to overcome the limits imposed by this mechanism are discussed. The alumina prepared with the addition of glucose is checked to be suitable as support for a Pt/Al2O3 catalyst prepared by impregnation with a basic solution.

The catalytic properties and structural characterization of catalysts derived from hypercrosslinked polystyrene (HPS), a polymer exhibiting mesoporosity and loaded with ruthenium in various amounts are investigated in the oxidation of d -glucose to d -gluconic acid. Transmission electron microscopy, X-ray fluorescence analysis, nitrogen physisorption measurements, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, EXAFS, XANES and catalytic studies show the presence of catalytically active nanoparticles of mixed composition (metal/oxide) with a mean diameter of 1.0–1.2 nm. The most active catalyst is found to contain 0.74 Ru wt.%. The highest selectivity to d -gluconic acid is 99.8% for a conversion of d -glucose of 99%; the specific activity of the catalyst is measured to be 1.13 × 10 −3 mol mol −1 Ru s −1 . The high-catalytic activity is attributed to the presence of pores of various sizes which facilitate mass transport and the high stability is attributed to the presence of small mesopores that have high-sorptional capacity and hinder the migration of the nanoparticles.

Synthesis of neutral complexes of Ni{sup 2+} with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH){sub 2} toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate){sub 2}(H{sub 2}O){sub 2}]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH){sub 2} sheets arrangements, assigned to the substitution of Cl{sup -} ions to OH{sup -} ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 deg. C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate){sub 2}(H{sub 2}O){sub 2}], but with a different crystal structure, is also formed. Spectroscopic resultsmore » may suggest a structure involving bridging ligands. - Graphical abstract: Ni(OH){sub 2} solid precursors can be readily selected on the basis of their defects, themselves stemming from the nickel salt chosen for precipitation, to rapidly synthesize neutral Ni(II)-aminoacid complexes by ligand-promoted dissolution.« less

The sorption of Cu on five vineyard soils was examined via macroscopic and spectroscopic investigations. The composition of the soils was previously determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) was employed to determine the metal environment with regard to the identity and interaction of the nearest atomic neighbors, the bond distances, and the coordination numbers. The five soils present similar sorption properties and there is no XAS evidence that the nature of the soil samples affects the local chemical environment of Cu(II). The kinetics of the Cu sorption reactions is rapid, with the equilibrium loading of Cu on the surface achieving approximately 200 μmol g−1, i.e., 12.7 mg g−1. The XAS data indicate that Cu is adsorbed in the form of inner-sphere complexes with first shell Cu O parameters of four equatorial Cu O bonds equal to 1.93 A and two axial Cu O bonds at 2.43 A. This is in accordance with a Jahn–Teller distorted octahedron environment around copper. Our results provide evidence of the complexation of Cu(II) onto soil organic matter coated with an inorganic surface (quartz, clay, and goethite).

The thermal reduction of Co/Al2O3 catalysts prepared by impregnation of Co(II) nitrate generally leads to migration of cobalt ions into alumina with formation of cobalt aluminate. In order to prevent the latter, it is attempted to reduce cobalt by decomposition of supported precursor salts containing ethylenediamine (en), a procedure successfully applied earlier to nickel. Alumina is impregnated with an aqueous solution containing Co(II) nitrate and two or three equivalents of en. After drying, several cobalt compounds are detected on the support by X-ray diffraction, diffuse reflectance UV-vis spectroscopy and X-ray absorption spectroscopy: crystals of [Co(III)(en)3](NO3)3 whatever the initial en/Co stoichiometry, Co(II) and Co(III)-en complexes, grafted or not, as well as a Co(II)(OH)2-like phase. The composition of these phases reveals that dramatic evolutions in cobalt speciation have taken place in the impregnating solution, driven by the oxidation of complexed cobalt by dissolved oxygen and by the precipitation of the Co(III) salt. Decomposition of these phases in an inert gas atmosphere does not lead to metal particles exclusively, as is the case of nickel, but to a mixture of oxidic and metallic phases. A treatment in hydrogen at 500 °C completes cobalt reduction, leading to 6-20 nm metal particles. This rather broad size distribution is linked to the wide range of cobalt species on the support, which stems itself from the coordination chemistry of cobalt bonded to ethylenediamine in aqueous solutions.

The effect of water on cobalt speciation in the synthesis of Co2+/ZSM5 catalysts is quantitatively studied by the combined use of macroscopic and local characterization techniques, TPR and X-ray absorption spectroscopies, respectively. The addition of a small quantity of water to cobalt acetate and zeolite during the preparation of Co2+/ZSM5 by solid-state reaction favors cobalt dispersion and migration into the zeolite. It also inhibits the formation of extraframework phases (Co3O4 particles, cobalt phyllosilicate). Dissociation of solid cobalt acetate upon contact with water is thought to be the driving force for enhanced cobalt migration into the zeolite.

This contribution presents the molecular approach used to investigate the different preparation steps of important catalytic systems, based on Mo, Ni, and Co. The first preparation step consists of impregnating oxide supports by aqueous solutions of transition-metal complexes (TMCs), called precursor complexes, and involves the liquid-solid (wet) interface. The following steps consist of thermal activation treatments, involving the gas-solid (dry) interface. The molecular approach is based on (i) the use of the TMC to monitor and probe the nature of its own interactions with the oxide support, (ii) the selection of the most appropriate techniques to monitor such interactions, and (iii) the design of experiments to identify and isolate the key parameters controlling the "TMC-oxide support" interactions. Physical techniques play a key role in the characterization of catalyst preparation both at the macroscopic [temperature-programmed reduction (TPR), X-ray diffraction (XRD)] and molecular [Raman, X-ray absorption near-edge spectroscopy-extended X-ray absorption fine structure (XANES)-EXAFS, diffuse reflectance UV-vis] levels, particularly when they are used simultaneously. They give some insight into the structure of the species existing on the surface, with the oxide support behaving as a solid ligand, when exposed for a short time to the precursor complex solution or after thermal treatment, or, for longer contact times, as a reactant.

International audience; Knowledge of the structure and composition of the solid phases of a soil is needed to understand the retention mechanisms of transition metals or organic pollutants on the molecular scale. With this aim, the characterization of a soil sample from the Champagne-Ardenne region was carried out using various non-destructive methods such as X-ray diffraction (XRD), transmission electron microscopy-energy dispersive X-ray spectrometry (TEM-EDX), Mössbauer and electron paramagnetic resonance (EPR) spectroscopies, X-ray photoelectron spectroscopy (XPS), and protometric studies. The combination of these techniques allowed us to obtain a precise knowledge of the solid structure and composition. We showed that soil particles consist of quartz, alumino-silicate and goethite which are partially covered by organic matter. XPS spectra showed that organic matter is preferentially coated onto an alumino-silicate surface. EPR spectroscopy revealed the presence of unexpected vanadyl moieties in the organic matter. Acid-base titrations provided information on available surface sites (0.25 mmol ¥ g-1, i.e. 2.25 sites per nm2), and the point of zero charge pHzpc (3.9).

1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina.

Co2+/ZSM5 catalysts (Co/Al = 1, overstoichiometric ratio) have been prepared by solid-state reaction at 500 °C in argon from H-ZSM5 and four Co(II) precursors: formate, nitrate, chloride and acetate. Co3O4 particles supported by the zeolite grains are the only cobalt-containing phases detected when formate is used. When cobalt nitrate is the precursor, Co3O4 particles appear to be independent from the grains. A fraction of cobalt has nevertheless migrated into the zeolite; this is linked with [Co(H2O)6](NO3)2 low melting point and wetting of the zeolite grains by the molten salt at the beginning of the thermal treatment. Catalysts prepared from cobalt chloride contain both nanometric Co3O4 particles on the support grains and cobalt ions inside the zeolitic channels. Ion exchange is possible, at least partly, due to the fact that unlike nitrate and formate, cobalt chloride has not decomposed before reaching the temperature at which the exchange process is activated. This process is chemically driven by the release of HCl in the gas phase. Finally, the major phase detected when cobalt acetate is the precursor is a poorly organized cobalt phyllosilicate surrounding zeolite grains. Acetate ions attack the zeolitic framework from outside during the solid-state reaction; cobalt ions are inserted in the silicate matrix and progressively migrate deeper in the grains upon thermal activation.

The binding ability of a lignocellulosic substrate extracted from wheat straw with chromium(III) ion was investigated. The study was carried out at macroscopic and microscopic scales. The adsorbent used was first characterised using X-ray diffraction and electron microscopy. Then, macroscopic studies were conducted using batch adsorption experiments, at room temperature, as a function of time, pH, and metal concentration. The results obtained indicate that several successive phenomena take place at the substrate surface. Indeed, sorption, co-precipitation, and precipitation processes arise depending on the experimental conditions. The speciation of Cr was also investigated, at the atomic scale, by EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES). This study revealed that chromium(III) surface complexes have an octahedral geometry. Chromium ions are held in inner-sphere complexes, and are coordinated to six oxygen atoms at an average distance of 1.90 A.

A Ni0 (15 wt %)/Al2O3 catalyst is prepared by impregnation using [Ni(en)2(H2O)2](NO3)2 as precursor salt containing the chelating ligand ethylenediamine (en). Due to the low solubility of this salt and the high viscosity of its solution, large crystals of the salt deposit on the support, clogging the porosity of alumina. These crystals split during the thermal treatment in argon; hydrogen produced in situ from organic residues reduces quantitatively nickel (II) to monodisperse small Ni0 particles, compared with only one half of nickel reduced by hydrogen when catalysts are prepared from [Ni(H2O)6](NO3)2. To cite this article: F. Negrier et al., C. R. Chimie 6 (2003).

In the light-off temperature range of methane total oxidation (250–600°C), two types of Pt/δ-Al 2 O 3 catalysts prepared from H 2 PtCl 6 or Pt(NH 3 ) 4 (OH) 2 show different catalytic behaviors. Initially very active, fresh chlorine-free catalysts deactivate in isothermal conditions of reaction, while fresh chlorine-containing catalysts, initially poorly active, undergo an activation with time on stream. Consequences of dechlorination of chlorine-containing catalysts and of impregnation by various amounts of NH 4 Cl on both types of catalysts are examined. Chlorine is responsible for the inhibition observed on ex-H 2 PtCl 6 catalysts, which could be attributed, more specifically, to the chloride ions remaining at the platinum–support interface after reduction of platinum. After aging of the catalysts under reaction, sintering of the platinum particles is observed on all samples, regardless of their preparation mode. This phenomenon is linked to the presence of oxygen in excess in the gas phase and can account for the deactivation of chlorine-free catalysts. The water produced during the reaction removes the inhibiting chlorine on all chlorine-containing catalysts. The activity of the largest sintered particles is shown to vary with the nature of the fresh catalyst, the aged ex-H 2 PtCl 6 catalysts giving the best results: the molecular nature of the fresh catalyst would also affect the activity of the stable aged catalyst. Both the initial presence of chloride ions at the metal–support interface and the composition of the reacting mixture are key factors to this positive reconstruction.

Methane oligomerization to alkanes can be accomplished on supported platinum via a two-step procedure: formation of carbonaceous species on the metallic surface by methane adsorption, followed by hydrogenation of these species. Temperature-programmed oxidation (TPO) experiments performed after hydrogenation steps of various durations show that the hydrogenation of a carbonaceous deposit obtained at 300 C on the reference Pt/SiO{sub 2} catalyst EUROPt-1 is not a fast process. Two groups of surface carbonaceous species have been characterized through their different reactivities toward oxygen, but at 300 C their reactivities toward hydrogen are similar. Among alkanes up to C{sub 5}, methane is the main product of hydrogenation, corresponding to one-half of the surface carbon reactive toward hydrogen; linear and branched alkanes are produced from the other half of the reactive carbonaceous species. On EUROPt-1, mainly ethane and n-pentane are produced during the first minutes of reaction, while on a sintered catalyst the initial production in n-pentane is negligible. The release of n-pentane during an intermediate purge with inert gas on EUROPt-1 shows that C-C bonds can form already during methane adsorption, leading to C{sub 5} precursors on specific active sites of this catalyst. A model of formation of C{sub 5} precursors is proposedmore » by analogy with the organometallic chemistry of molecular hydrocarbon platinacycles. The subsequent production of alkanes (C{sub 2} > C{sub 3} > C{sub 4} > C{sub 5}) could be described through a statistical model of dynamic coupling between carbonaceous species involving hydrogen, rather than by hydrogenolysis of heavier carbonaceous species. However, this latter mechanism is likely to predominate for the production of C{sub 6}-C{sub 8} compounds.« less

Residual chlorine ions on a Pt/Al2O3 catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size.