Search

Localization and migration of highly mobile and extremely efficient bismuth promoter in iron Fischer–Tropsch catalysts were elucidated using in situ methods., Liquid metals are a new emerging and rapidly growing class of materials and can be considered as efficient promoters and active phases for heterogeneous catalysts for sustainable processes. Because of low cost, high selectivity and flexibility, iron-based catalysts are the catalysts of choice for light olefin synthesis via Fischer–Tropsch reaction. Promotion of iron catalysts supported by carbon nanotubes with bismuth, which is liquid under the reaction conditions, results in a several fold increase in the reaction rate and in a much higher light olefin selectivity. In order to elucidate the spectacular enhancement of the catalytic performance, we conducted extensive in-depth characterization of the bismuth-promoted iron catalysts under the reacting gas and reaction temperatures by a combination of cutting-edge in situ techniques: in situ scanning transmission electron microscopy, near-atmospheric pressure X-ray photoelectron spectroscopy and in situ X-ray adsorption near edge structure. In situ scanning transmission electron microscopy conducted under atmospheric pressure of carbon monoxide at the temperature of catalyst activation showed iron sintering proceeding via the particle migration and coalescence mechanism. Catalyst activation in carbon monoxide and in syngas leads to liquid bismuth metallic species, which readily migrate over the catalyst surface with the formation of larger spherical bismuth droplets and iron–bismuth core–shell structures. In the working catalysts, during Fischer–Tropsch synthesis, metallic bismuth located at the interface of iron species undergoes continuous oxidation and reduction cycles, which facilitate carbon monoxide dissociation and result in the substantial increase in the reaction rate.

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.

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

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.

Melt infiltration (MI) has been described as an effective way to disperse transition metals (TM) in ordered mesoporous supports. The alternative method described here is based on the infiltration of molten precursors into the support pores in the presence of a support polymer porogen. The resulting materials contain metal oxide particles (metallic particles after reduction) smaller than 2 nm, dispersed within the support micropores, which prove to be stable upon reduction up to 900 °C and to exhibit improved catalytic performances for the hydrogenation of cinnamaldehyde due to the high fraction of the active metal exposed.

Successfully modeling the behavior of catalytic systems at different scales is a matter of importance not only for a fundamental understanding but also for a more rational design of catalysts and a more precise definition of the kinetic laws used as inputs in chemical engineering. We have developed here a multiscale modeling of the dehydration of isopropyl alcohol to propene and diisopropyl ether on γ-alumina catalysts, which clearly evidences and explains the central character of cooperative effects between coadsorbates in the kinetic network. The evolution of partial pressures with contact time was simulated using an original DFT-based microkinetic model based on a “macro site” centered on the main active site located on the (100) planes of alumina and comprising several neighboring adsorption sites. The formation of isopropyl alcohol–isopropyl alcohol or water–isopropyl alcohol dimers on the surface was required to correctly simulate the production of the minor product, diisopropyl ether, and the evolu...

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.

International audience; This chapter gives an overview of the current preparation strategies for the synthesis of bulk and supported metal oxide catalysts, in order to give rational guides to understand the synthetic challenges associated with the preparation of these catalytic systems developed in the successive chapters. Bulk and mixed oxides syntheses for catalysis are reviewed with a presentation of the main synthesis strategies and of novel routes implemented, with a focus on the control of the textural properties of the materials for simple oxides and on two classes of mixed oxides: perovskites and hexaaluminates, that are particularly interesting for high temperature reactions. The final section concentrates on the synthesis of supported metal oxide catalysts, with a particular emphasis on the discussion of the interfacial chemistry occurring at the solid–liquid interface during the first steps of the deposition of an active oxide phase on a high-surface area support.

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.

77 FIELD Section Title:Magnetic Phenomena Laboratoire de Reactivite de Surface (UMR 7197, CNRS), UPMC (Universite Pierre et Marie Curie), Paris, Fr. FIELD URL: written in English; Following procedures formerly developed for the prepn. of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles dispersed on porous alumina have been prepd. by impregnation of γ-Al2O3 with (NH4)2[Co(EDTA)] and thermal decompn. in inert atm. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way by the EDTA ligand. The thermal treatment at 400-900 °C leads to the EDTA ligand decompn. and recovering of the support porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox reactions between the org. ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterization by transmission electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temp. leads to an increase of the degree of cobalt redn. as well as to a growth of the cobalt metal particles. As a consequence, the samples prepd. at 400-700 °C exhibit superparamagnetism and a satn. magnetization of 1.7-6.5 emu g-1 at room temp., while the sample prepd. at 900 °C has a weak coercivity (0.1 kOe) and a satn. magnetization of 12 emu g-1. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating in H2 at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles are protected from chem. aggression and sintering by their coating. [on SciFinder(R)]

The alpha-dicarbonyl contents of commercial honey samples from different botanical origins were analyzed as their quinoxaline derivatives using HPLC-DAD, HPLC-MS, HPLC-MS/MS, and HPLC-TOF-MS. A total of nine such compounds were detected, of which five were previously reported in honey (glucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, and 2,3-butanedione) and three were reported only from sources other than honey [3-deoxypentulose, 1,4-dideoxyhexulose, and 3,4-dideoxyglucoson-3-ene (3,4-DGE)]. An unknown alpha-dicarbonyl compound was also tentatively identified as an oxidation product of 3,4-DGE and was termed 3,4-dideoxyglucosone-3,5-diene (3,4-DGD). Only glyoxal (0.3-1.3 mg/kg), methylglyoxal (0.8-33 mg/kg), and 2,3-butanedione (0-4.3 mg/kg) were quantified in all honey samples. Furthermore, analysis of the alpha-dicarbonyl profile of various honey samples indicated that certain alpha-dicarbonyl compounds are found in specific honey samples in much higher proportions relative to the average amounts. The free radical scavenging activity as measured by DPPH method has also indicated that the darker honey samples such as buckwheat, manuka, blueberry, and eucalyptus had higher antioxidant properties compared to lighter-colored samples.

Ni (15 wt%)/Al 2 O 3 catalysts prepared by decomposition of supported Ni(II)–ethylenediamine complexes in inert atmosphere, followed by post-treatment in hydrogen, are able to catalyze carbon monoxide hydrogenation at temperatures lower than for a catalyst prepared from nickel nitrate and containing a fraction of surface nickel aluminate. Unlike the latter, the catalyst prepared from Ni(II)–en complexes exhibits mostly surface metallic sites and is more stable under reaction despite the absence of nickel aluminate. Deactivation occurs during the reaction, probably by carbon deposition, but less strongly than for an ex-nickel nitrate catalyst.

Ni (7 wt%)/Al2O3 catalysts prepared by decomposition of Ni(II)-ethylenediamine complexes in inert atmosphere initially contain a mixture of metallic and oxidized nickel. X-ray photoelectron spectroscopy shows that after a hydrogen treatment at 500 °C, the system contains more metallic nickel than catalysts prepared from the usual precursor, nickel nitrate. Carbonaceous species resulting from the partial oxidation of ethylenediamine are also eliminated. The catalyst post-treated in hydrogen exhibits a high metallic surface area accessible to reactants and is able to catalyze CO methanation.

Nanoparticles of Co–Ni alloys were prepared by thermal decomposition of layered double hydroxides (LDH) containing co-intercalated complexes of two metals. The precursor compounds [LiAl2(OH)6]2{Ni1−xCox(EDTA)} · 4H2O (where EDTA is ethylenediaminetetraacetate) obtained by anion exchange from [LiAl2(OH)6]Cl · 1.5H2O were treated at 450 °C in vacuum. The microstructure of the thermal products was studied using local (TEM, SAED, EDX) as well as integral (XRD, SAXS) methods. It was found that Ni–Co alloy nanoparticles are formed uniformly dispersed in the carbonized matrix of lamellar mixed oxides, and the increase of the relative cobalt content in Ni1−xCox from x = 0 to 0.86 leads to gradual enlargement of the average alloy particle size from 9 to 16 nm. According to magnetic measurements by SQUID magnetometry and FMR, all alloys, except Ni0.14Co0.86, are superparamagnetic at room temperature. The results on particle size obtained by different techniques are in good agreement. The variation of nanoparticle size via chemical composition in alloys and the use of LDH intercalation matrices is a promising way to synthesize nanocomposites with target properties.

Hydration of gamma-Al2O3 is often reported to occur via the superficial transformation of the alumina surface into aluminum hydroxide-like layers. However, very little evidence has been given so far to support this hypothesis. It is demonstrated here by X-ray diffraction, TEM, electron diffraction, and solubility studies that a second process of hydration takes place that involves the dissolution of alumina and subsequent precipitation of well-shaped Al(OH)3 particles from supersaturated alumina aqueous solution. This process can be observed on a macroscopic scale (XRD, TEM) for any pH5, provided that the contact time between alumina and water exceeds 10 h. The least thermodynamically stable phase of aluminum hydroxide, bayerite, becomes favored compared with gibbsite when the pH of the solution is increased. It is assumed that the rate of formation of bayerite germs is greater than that of gibbsite due to variations in aluminum speciation in solution as a function of pH.

The decomposition in flowing argon of the neutral complex [Ni II (glycinate) 2 (H 2 O) 2 ] leads to a mixture of face-centered cubic (fcc) and hexagonal close-packed (hcp) metallic nickel. The latter is the main phase when the Ni(II) complex is supported on alumina. Unlike most hexagonal Ni phases described earlier, and similar to hexagonal Ni 3 C, the unit cell parameters ( a = 0.2493 and c = 0.4084 nm ) lead to Ni–Ni distances equal to those encountered in fcc Ni. TEM shows that the nanoparticles are protected by graphite layers, whose elimination by heating in hydrogen results in transformation to the fcc phase and crystal growth. Magnetic measurements provide evidence of the coexistence of superparamagnetic and ferromagnetic nanoparticles. This result is in line with the broad size distribution observed by TEM and is interpreted on the basis of the metallic character of hcp Ni particles.

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

When CO2+/ZSM5 catalysts are prepared by solid state exchange between H-ZSM5 and cobalt acetate, CO2+ ions form layered cobalt phyllosilicate at the surface of the zeolite grains, bringing about a reassessment of the chemistry involved in the preparation of catalytic systems by solid state exchange.

Summary Objective A common rodent model in epilepsy research employs the muscarinic acetylcholine receptor (mAChR) agonist pilocarpine, yet the mechanisms underlying the induction of pilocarpine-induced seizures (PISs) remain unclear. Global M1 mAChR (M1R) knockout mice are resistant to PISs, implying that M1R activation disrupts excitation/inhibition balance. Parvalbumin-positive (PV) inhibitory neurons express M1Rs, participate in cholinergically induced oscillations, and can enter a state of depolarization block (DB) during epileptiform activity. Here, we test the hypothesis that pilocarpine activation of M1Rs expressed on PV cells contributes to PISs. Methods CA1 PV cells in PV-CRE mice were visualized with a floxed YFP or hM3Dq-mCherry adeno-associated virus, or by crossing PV-CRE mice with the RosaYFP reporter line. To eliminate M1Rs from PV cells, we generated PV-M1knockout (KO) mice by crossing PV-CRE and floxed M1 mice. Action potential (AP) frequency was monitored during application of pilocarpine (200 μm). In behavioral experiments, locomotion and seizure symptoms were recorded in wild-type (WT) or PV-M1KO mice during PISs. Results Pilocarpine significantly increased AP frequency in CA1 PV cells into the gamma range. In the continued presence of pilocarpine, a subset (5/7) of PV cells progressed to DB, which was mimicked by hM3Dq activation of Gq-receptor signaling. Pilocarpine-induced depolarization, AP firing at gamma frequency, and progression to DB were prevented in CA1 PV cells of PV-M1KO mice. Finally, compared to WT mice, PV-M1KO mice were associated with reduced severity of PISs. Significance Pilocarpine can directly depolarize PV+ cells via M1R activation, but a subset of these cells progress to DB. Our electrophysiologic and behavioral results suggest that this mechanism is active during PISs, contributing to a collapse of PV-mediated γ-aminobutyric acid (GABA)ergic inhibition, dysregulation of excitation/inhibition balance, and increased susceptibility to PISs.

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)]

Mesoporous aluminas can be prepared using organic additives as porogens even if these are not surfactants, as is the case for glucose. It is shown here that porosity arises from glucose entrapped in the material precipitated at the beginning of the synthesis, and subsequently caramelized. After impregnation by nickel(II) salts and calcination, more difficult-to-reduce nickel aluminate is detected on mesoporous aluminas than on commercial aluminas, because the surface area exposed to water is larger in the former case. The presence of citrates in the impregnating solution helps to lower the proportion of nickel aluminate, but may also lead to larger NiO particles.

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)]

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 A.

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 sections in this article are Deposition of Active Component Precursors Ion Exchange: Physicochemical Aspects Impregnation: Physical Aspects Support and Precursor during the Preparation Steps: Chemical Aspects Applications Conclusions Keywords: impregnation; ion exchange; pH; precursor speciation; reforming catalysts

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