The crystal chemistry of hydrotalcite-like compounds is investigated by powder diffraction methods such as Rietveld structure refinement, radial distribution function analysis, atom-specific radial distribution analysis obtained from anomalous diffraction data, and EXAFS spectroscopy. The topology of the brucite-type layer as well as the layer stacking arrangement and the intralayer bonding are determined for Mg,Al, Mg,Ga, and Ni,Al systems. The occurrence of long-range cation ordering in materials with M(II)/M(III) cation ratios close to 2.0 is observed only for systems with similar cation radii, and it is associated with a corrugation of the octahedral layer. The lack of ordering for systems with highly different cation radii is ascribed to the layer compression exhibited by these compounds, which prevents the layer distortion. The stacking arrangement is random for the solids investigated, except for the Mg,Al system which shows a preference for the rhombohedral polytype. It is proposed that this behavior is related to the extent of local directional bonds between the oppositely charged layers.

The structure of the phases obtained upon dehydration and decomposition of hydrotalcite-like compounds is investigated by several experimental techniques. A reaction mechanism is proposed encompassing a change in coordination of the M(III) cations during the dehydration step. The formation of a 3-dimensional structure occurs upon the subsequent decomposition of the interlayer anions and dehydroxylation of the octahedral layers. In the decomposed material the cations are trapped in the interstices of a regular oxygen cubic close packed lattice and exhibit a considerable disorder. Strains develop during the decomposition, which are likely related to the observed increase of surface area. The thermal stability of the decomposed materials is connected to the reduced cation diffusivity in the oxygen lattice.

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From an experimental point of view and more particularly in heterogeneous catalysis, the LIII white line is at the center of electronic charge transfer either between either the nanometer scale metallic particle and the support or between the two metals which are present inside the cluster. In this work, we show that a strong correlation exists between the intensity of the white line and the size of the cluster. Thus, at least two physical phenomenon can affect the intensity of the white line:  the size of the cluster, which can be considered as an intrinsic effect (density of state of nanometer scale platinum cluster are far from the bulk one), and a possible charge transfer between the cluster and the support, which can be considered as an extrinsic one. If the first results obtained with the FeFF program are encouraging, it is clear that to go further in the analysis, the detailed geometric configurations present in the cluster surface have to be integrated very precisely in order to obtain quantitative effects that would be more clearly related to the characteristics of the density of states.

Résumé -Microstructure de catalyseurs Fischer-Tropsch à base de cobalt supporté -La structure de particules métalliques de cobalt supporté sur silice ou sur alumine, et en présence ou non d'un promoteur (Ru), a été étudiée in situ par diffraction des rayons X conventionnelle et anomale. Par comparaison avec des diagrammes simulés, il est montré que cette structure est caractérisée par la présence de défauts d'empilement dont la densité est directement reliée à la température de réduction du cobalt. Des traitements de carburation/décarburation sous CO et H 2 nous ont permis de modifier de manière contrôlée la microstructure du cobalt métallique pour un même support tout en limitant la variation de la taille des particules. Quel que soit le support, et en présence ou non d'un promoteur, les basses températures de réduction favorisent la formation de la forme hexagonale compacte du cobalt, alors qu'une réduction à haute température favorisera la forme cubique faces centrées. Dans les conditions de la synthèse Fischer-Tropsch, les catalyseurs contenant du cobalt à forte densité d'empilements de type hexagonal compact montrent une activité en conversion du CO nettement supérieure à celle des catalyseurs majoritairement cubiques. Abstract -Microstructure of Supported Cobalt Fischer-Tropsch Catalysts -The structures of metallic cobalt particles supported on silica (with and without Ru promoter) and on alumina have been investigated in-situ by conventional and anomalous X-ray diffraction.Comparison with simulated XRD patterns shows the structure to consist of a defect phase characterised by the presence of stacking faults, the density of which is directly related to the temperature at which the cobalt oxide is reduced.

Drug-induced calculi represent 1-2% of all renal calculi. The drugs reported to produce calculi may be divided into two groups. The first one includes poorly soluble drugs with high urine excretion that favour crystallisation in the urine. Among them, drugs used for the treatment of patients with human immunodeficiency, namely atazanavir and other protease inhibitors, and sulphadiazine used for the treatment of cerebral toxoplasmosis, are the most frequent causes. Besides these drugs, about 20 other molecules may induce nephrolithiasis, such as ceftriaxone or ephedrine-containing preparations in subjects receiving high doses or long-term treatment. Calculi analysis by physical methods including infrared spectroscopy or X-ray diffraction is needed to demonstrate the presence of the drug or its metabolites within the calculi. Some drugs may also provoke heavy intra-tubular crystal precipitation causing acute renal failure. Here, the identification of crystalluria or crystals within the kidney tissue in the case of renal biopsy is of major diagnostic value. The second group includes drugs that provoke the formation of urinary calculi as a consequence of their metabolic effects on urinary pH and/or the excretion of calcium, phosphate, oxalate, citrate, uric acid or other purines. Among such metabolically induced calculi are those formed in patients taking uncontrolled calcium/vitamin D supplements, or being treated with carbonic anhydrase inhibitors such as acetazolamide or topiramate. Here, diagnosis relies on a careful clinical inquiry to differentiate between common calculi and metabolically induced calculi, of which the incidence is probably underestimated. Specific patient-dependent risk factors also exist in relation to urine pH, volume of diuresis and other factors, thus providing a basis for preventive or curative measures against stone formation.

An original preparation method, called “two solvents” method, allows the production of MnO2 nanowires patterned by SBA-15 silicas under mild conditions, with a preserved two-dimensional hexagonal structure, a 97% filling of the porosity by oxide nanowires, and a controlled microstructure. A comparison is made with Mn-loaded SBA-15 prepared by more conventional adsorption methods. In the latter case, MnO x particles inside and outside the silica grains, empty and filled mesopores, and several Mn oxides (MnO2, Mn2O3, and Mn3O4) were identified. Once the preparation method of Mn-loaded SBA-15 optimized, various X-ray scattering and adsorption techniques using synchrotron radiation were used to observe salient features of the MnO2 nanowires crystallization in situ upon calcination. X-ray absorption at the Mn K edge shows that the oxidation state of manganese increases from (II) to (IV) between 80 and 120 °C. The oxidation of the Mn(II) salt occurs at a temperature lower than that necessary for bulk manganese nitrate (200 °C), which confirms its confinement within the SBA-15 pores. β-MnO2 nanowires of defective pyrolusite type are identified by wide-angle diffraction. The comparison between diffraction results and simulations demonstrates that the nanowire diameter is similar to the mesopore diameter of the silica host. A small contraction of unit-cell parameters occurs upon the crystallization of β-MnO2 nanowires. A parallel overall intensity increase observed in small-angle X-ray diffraction is the fingerprint of a homogeneously filled porosity.