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Abstract: Using density functional theory periodic calculations, we investigate the effects of two relevant supports for industrial hydrodesulfurization catalysts, anatase (titania) and γ-alumina, on the thermodynamic stability of Mo6S n ( to 24) clusters representing the MoS2 active phase. Under HDS conditions, anatase surfaces stabilize more sulfur-deficient small clusters than alumina surfaces. Because of an epitaxy relationship, the anatase surfaces also enhance tilted and perpendicular cluster orientations. For large cluster sizes, we establish a model extrapolating the energetic properties obtained on supported Mo6S n clusters that reveals how the nature of the chemical interaction of the MoS2 single layer is modified. A concept based on competing “ligand effects” between the support and the gas phase on the active phase is proposed to explain our results. These new insights are in line with the higher intrinsic HDS activity reported for the anatase-supported MoS2 catalyst. [Copyright &y& Elsevier]

Abstract: In the same spirit as a recent periodic DFT study on the interaction of MoS2 layers on γ-alumina and anatase-TiO2 surfaces [C. Arrouvel et al., J. Catal. 232 (2005) 161], the present DFT investigation brings new insights comparing the thermodynamic stability of MoS2 particles anchored by S-edge and Mo-edge on these two supports under HDS conditions. It is shown that the S-edge interacts more weakly with the γ-alumina and anatase-TiO2 surfaces. In particular, the epitaxial relationship found for the Mo-edge is not recovered for the S-edge on anatase. The determination of adhesion energies of Mo5CoS n clusters on the two supports shows that Co weakens the edge anchoring of the active phase. The equilibrium morphology and the edge-wetting regime of the supported MoS2 particles are deduced using the Gibbs–Curie–Wulff formalism. The DFT results combined with the morphological models of supported particles lead to a precise evaluation of the proportion of anchored and free edge sites (including the relative distribution of S-edge and Mo-edge sites). This analysis provides a new interpretation based on the edge-wetting concept of the two supports by MoS2 and CoMoS particles to explain the different HDS activities observed. [Copyright &y& Elsevier]

Abstract: We use a multitechnique approach to reveal how the nature and concentration of surface acid–basic OH groups present on anatase-TiO2 nanocrystallites depend on their morphologies. Coupling recent density functional theory (DFT) calculations with three physical characterization techniques (X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy), the different infrared (IR) spectroscopic properties of two anatase samples are explained by morphology effects resulting from the synthesis pathways. Whereas a conventional route leads to anisotropic shapes, the multigelation method leads to more “spherical” shapes. As shown by the DFT calculations, the assignment of the OH stretching bands depends on the surfaces exposed by the anatase-TiO2 nanocrystallites. The signature of the nanocrystallites morphology can thus be captured by IR spectroscopy. [Copyright &y& Elsevier]

A comparative investigation of surface hydroxylation states for anatase–TiO2 and γ-alumina is crucial for a better understanding of how these materials behave as catalytic supports under working conditions. Our approach combines density functional simulations and thermodynamic analysis, to determine the types of hydroxyls existing on the (100), (101), (001), and (110) surfaces of anatase–TiO2, as a function of temperature and water pressure. The vibrational analysis of surface OH groups allows for the assignment of experimental infrared bands as a function of the surface orientation. A consistent and quantitative comparison with recent DFT simulations on γ-alumina highlights the different acidic–basic properties of the two supports. Finally, we suggest directions for increasing the density of basic and exchangeable hydroxyls which is governed by morphology effects. [Copyright &y& Elsevier]

Intellectual disability coupled with epilepsy are clinical hallmarks of the creatine (Cr) transporter deficiency syndrome resulting from mutations in the SLC6A8 gene. So far characterization of pathogenic mutations of SLC6A8 has been limited to Cr uptake. The aim of our study was to characterize the electrogenic and pharmacological properties of non truncating SLC6A8 mutations identified in patients presenting variable clinical severity. Electrophysiological and pharmacological properties of four mutants (including two novel ones) were studied in X. laevis oocyte expression system. Creatine uptake was assessed with [(14)C]-Cr in X. laevis and patients' fibroblasts. Subcellular localization was determined by immunofluorescence and western blot. All mutants were properly targeted to the plasma membrane in both systems. Mutations led to the complete loss of both electrogenic and transport activities in X. laevis and Cr uptake in patients' fibroblasts. Among the Cr analogs tested, guanidinopropionate induced an electrogenic activity with the normal SLC6A8 transporter similar to creatine whereas a phosphocreatine derivative, PCr-Mg-CPLX, resulted in partial activity. SLC6A8 mutants displayed no electrogenic activity with all Cr analogs tested in X. laevis oocytes. Although the mutations altered various domains of SLC6A8 Cr uptake and electrogenic properties were completely inhibited and could not be dissociated. Besides the metabolic functions of Cr, the loss of SLC6A8 electrogenic activity, demonstrated here for the first time, may also play a role in the altered brain functions of the patients.

Fumarase deficiency (FD), caused by biallelic alteration of the Fumarase Hydratase gene (FH), and a rare metabolic disorder that affects the Krebs cycle, causes severe neurological impairment and fumaric aciduria. Less than 30 unrelated cases are known to date. In addition, heterozygous mutations of the FH gene are responsible for hereditary leiomyomatosis and renal cell cancer (HLRCC). We report three additional patients with dramatically different clinical presentations of FD and novel missense mutations in the FH gene. One patient had severe neonatal encephalopathy, polymicrogyria, <1% enzyme activity, and mildly increased levels of urinary fumarate. The second patient had microcephaly, mental retardation, 20% of fumarase activity, and intermediate levels of urinary fumarate. The third patient had mild mental retardation, polymicrogyria, 42-61% enzyme activity in different cell types and massive amounts of urinary fumarate. In silico analysis predicted minor yet significant structural changes in the encoded proteins. The nuclear translocation of hypoxia-inducible factor (HIF)-1alpha (HIF1A) in cultured fibroblasts was similar to controls. These results extend the range of clinical and biochemical variation associated with FD, supporting the notion that patients with moderate increases in fumarate excretion should be investigated for this disease. The tumoral risk in the patients and their relatives requires adequate screening protocols., (© 2011 Wiley-Liss, Inc.)

The effect of confinement within some zeolitic structures on the activity and selectivity of metallocene catalysts for the ethylene oligomerization has been investigated using grand canonical Monte Carlo simulations (GCMC). The following zeolite (host) frameworks displaying different pore sizes, have been studied as solid hosts: mazzite (MAZ), AIPO-8 (AET), UTD-1F (DON), faujasite (FAU), and VPI-5 (VFI). Intermediates and transition states involved in the ethylene trimerization reaction catalyzed by a Ti-based catalyst [(η(5)-C(5)H(4)CMe(2)C(6)H(5))TiCl(3)/MAO] have been used as sorbates (guests). We have demonstrated linear correlations with slope a(H,j) between the adsorption enthalpy and the molecular volume V(m) of the sorbates, each holding for a given microporous host below a host-specific threshold V(mmax,j). Beyond this maximal molecular volume, the adsorption vanishes due to steric exclusion. a(H,j) increases, and V(mmax,j) decreases with decreasing host pore size, in line with the confinement concept. We moreover showed that, in the limit of vanishing loading (Henry regime), the enthalpies and entropies of adsorption in a given host are linearly correlated. We have defined a host-specific confinement compensation temperature a(j), which refers to a temperature where the stabilizing adsorption enthalpic interactions are canceled out against the loss in entropy. However, calculated a(j) are much larger than the operating temperatures. With a setup microkinetic model, we predict that the activity and selectivity of the confined Ti-catalyst in ethylene oligomerization can be significantly altered with respect to homogeneous phase conditions, since the adsorption free energies of transition states and intermediates also become functions of a(H,j) and V(m). We have applied this theory to predict the optimum host pore size to get maximum α-octene production, instead of α-hexene, which is primarily produced in the homogeneous phase. We also predict a significantly increased activity for confined catalysts.

The thermochemistry of chlorinated gamma-alumina surfaces is explored by means of density functional calculations as a function of relevant reaction conditions used in experiments and in high-octane fuel production in the refining industry such as hydrocarbon isomerization and reforming. The role of chlorine as a dope of the Brønsted acidity of gamma-alumina surfaces is investigated at an atomic scale. Combining infrared spectroscopy and density functional theory calculations, the most favorable location of chlorine atoms on the (110), (100) and (111) surfaces of gamma-alumina is found to result either from direct adsorption or from the exchange of basic hydroxyl groups. Moreover, the modification of the hydrogen bond network upon chlorine adsorption is put forward as a key parameter for changing the Brønsted acidity. In a second step, we use a thermodynamic approach based on DFT total energy calculations corrected by the chemical potentials of HCl and H2O to determine the adsorption isotherms of chlorine and the relative surface concentration of hydroxyl groups and chlorine species on the gamma-alumina surfaces. The determination of chlorine content as a function of temperature and partial pressures of H2O and HCl offers new quantitative data required for optimizing the state of the support surface in industrial conditions. The mechanisms of chlorination are also discussed as a function of reaction conditions.

The sodium cation is well known as an efficient poison of gamma-alumina surface acidity. This poisoning effect has been revealed both by characterization methods and catalytic tests. In this work, we propose an accurate model of sodium exchanged gamma-alumina surfaces. On realistic models of hydroxylated gamma-alumina surfaces, the location of sodium cation is determined by the use of density functional theory (DFT) methods. For the (100) and (110) surfaces of gamma-alumina, the sodium cation is found in a solvated state within an inner solvation sphere complex. Its coordination sphere is constituted by O-mu(2), O-mu(3) and HO-mu(1) surface groups. The stretching frequency of these HO-mu(1) groups is shifted, leading to the appearance of a new band predicted and observed at about 3754 cm(-1) on the IR spectrum.

Controlling gelation kinetics is an important objective for several applications (ceramic and thin film syntheses, reduction in permeability of porous rock, etc). There is a growing interest in studying the gelation of polymers by zirconium, a crosslinker of lower toxicity than the chromium which is still commonly used. XAS at the Zr K-edge was performed at the European Synchrotron Radiation Facility (ESRF) on the BM32 beamline. The fluorescence detection was used to carry out successful in situ speciation at concentrations as low as 36 ppm. The Zr speciation was determined both in ZrLa (where La stands for lactate) aqueous solutions and in gels of a terpolymer of acrylamide having 2% of zirconium reactive acrylate side groups and 2% of sulfonate groups introduced to prevent syneresis. XANES results show that Zr is always in a dodecahedral geometry. In ZrLa solutions. EXAFS results indicate that Zr species grow from a dimer Zr2(La)6 to a tetramer (Zr4(La)x) and then to larger polymers resulting from tetramer associations, as the Zr concentration decreases from 51840 ppm to 36ppm. In polymer gels, Zr species appear to be dimers at pH 6 while tetramers are found when gelation occurred at pH 7. Calculations taking into account multiple scattering effects as well as dynamic molecular calculation confirmed conclusions derived from conventional EXAFS analysis.