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Ayari F.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Mhamdi M.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Alvarez-Rodriguez J.,Spanish University for Distance Education (UNED) | Guerrero Ruiz A.R.,Spanish University for Distance Education (UNED) | And 2 more authors.
Applied Catalysis A: General | Year: 2012

Catalytic performances of Cr-ZSM-5 catalysts (5 wt.% of Cr, Si/Al = 26), prepared by solid-state reaction and aqueous exchange, from Cr nitrate and Cr acetate precursors, were evaluated in the selective ammoxidation of ethylene into acetonitrile in the temperature range 425.500 °C. Catalysts were characterized by chemical and thermal analysis, XRD, N 2 physisorption, 27Al MAS NMR, TEM, UV-vis DRS, Raman, DRIFTS and H 2-TPR. Characterization results shown that solid-state exchange was favorable for Cr 2O 3 formation, while exchanging chromium in aqueous phase led, essentially, to Cr(VI) species. Catalysts were actives and selectives in the studied reaction, and among them, those, prepared from aqueous exchange, exhibited the highest acetonitrile yields (23±0.5%, at 500 °C). Improved catalytic properties can be correlated with the chromium species nature. In fact, mono/di-chromates and/or polychromate species, sited in the charge compensation positions, were definitively shown, as being, the active sites. Furthermore, during solid-state reaction, the agglomeration of Cr 2O 3 oxide should be avoided since these species inhibit the catalyst activity. © 2011 Elsevier B.V. All rights reserved.


Ben Zid T.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Khedher I.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Fraile J.M.,University of Zaragoza
Journal of Chemical Research | Year: 2013

V/MCM-41 was prepared by impregnation of MCM-41, calcined at two different temperatures (550 and 750 °C), with vanadium (V) oxytriisopropoxide (VO(OiPr)3). The calcination temperature of the support controls the surface silanol density, leading to different surface organometallic species, as shown by different characterisation techniques, such as 29Si CP-MAS NMR, UV-Vis and FT-IR. Monopodal ≡SiO-VO(O iPr)2 and bipodal (≡SiO)2-VO(O iPr) species are the major ones in V-MCM750, whereas bipodal and tripodal (≡SiO)3-VO are the major ones in V-MCM550. Monopodal and bipodal species are more active in the oxidation of methyl phenyl sulfide with alkyl hydroperoxides, with higher selectivity to sulfoxide than tripodal ones, but at the same time they are more easily deactivated. It is possible to perform the enantioselective oxidation using (S,S)-(+)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediamine as chiral ligand, with the monopodal species being the most efficient.


Turki A.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Turki A.,Institute National Of Recherche Et Danalyse Physico Chimique | Kochkar H.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Kochkar H.,Center National Of Recherches En Science Des Materiaux Cnrsm | And 3 more authors.
Applied Catalysis B: Environmental | Year: 2013

The influence of the sodium content on thermal stability and photocatalytic activity of calcined titanate nanotubes (TNT) was herein evaluated by preparing different samples through hydrothermal treatment of TiO2 powder (P25) in a concentrated NaOH solution (11.25M) at 130°C during 20h followed by acid washing steps. Titanate nanotubes samples with sodium (Na-TNT) and sodium-free (H-TNT) were then obtained using different concentrations of HCl aqueous solutions namely 0.1M and 1M respectively. As synthesized nanomaterials with different Na percentages were then calcined at temperatures varying between 400°C and 700°C. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77K, thermal analysis (DTA, TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance spectroscopy (DRS). The photocatalytic activities of Na-TNT and H-TNT derived nanomaterials were then evaluated through the photocatalytic degradation of formic acid (FA).Results show that the presence of sodium retards the dehydration process during the transformation of titanate into TiO2 shifting the formation of anatase phase to higher temperatures. However, sodium is not necessary to preserve the nanotubular morphology. The presence of sodium after calcination strongly impacts negatively the photocatalytic properties. If sodium is completely removed from the initial titanate orthorhombic phase, calcination leads to TiO2 anatase materials with enhanced photocatalytic properties compared to P25 in the degradation of formic acid, particularly if nanotubular morphology is preserved. The highest activity was therefore achieved for the H-TNT sample calcined at 400°C. The photodegradation activity of formic acid depends on the specific surface areas and TiO2 crystallinity. In pure anatase nanoparticles the activity strongly decreases with coherent crystallographic domains ≥10nm. © 2013 Elsevier B.V.


Tonelli D.,University of Bologna | Ghorbel S.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Colombari M.,University of Bologna | Guadagnini L.,University of Bologna | Ghorbel A.,Laboratoire Of Chimie Des Materiaux Et Catalyse
Journal of Electroanalytical Chemistry | Year: 2013

An ion-selective electrode (ISE) for monohydrogen phosphate, based on a dispersion of Mg/Al hydrotalcite-like compound particles into a polymeric membrane of polyvinyl butyral, in the coated-wire configuration, is described. The inorganic ionophore was ad hoc synthesized and characterized. The electrode showed a Nernstian response towards monohydrogen phosphate independently from the pH of the solution in the range 4.5-7.8 with a linearity range from 5.0 × 10-5 to 2.0 × 10-2 M and a limit of detection of 3.0 × 10-5 M. The response time varied from 10 to 25 s. Potentiometric selectivity coefficients for the proposed sensor were evaluated over several mono- and divalent anions, chosen among the most common ones. The results pointed out a reasonably good selectivity for monohydrogen phosphate. A successful application of the developed ISE for phosphate determination in hydroxyapatite samples using direct potentiometry is presented. © 2012 Elsevier B.V. All rights reserved.


Mehri A.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Kochkar H.,Center National Of Recherches En Science Des Materiaux Cnrsm | Daniele S.,CNRS Research on Catalysis and Environment in Lyon | Mendez V.,CNRS Research on Catalysis and Environment in Lyon | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2012

One-pot deposition of Pd onto TiO 2 has been achieved through directly contacting palladium(II) salt with nanosized functionalized TiO 2 support initially obtained by sol-gel process using titanium isopropoxide and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various palladium salts (Na 2PdCl 4 and Pd(NH 3) 4Cl 2·H 2O) and titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used in order to study the effect of the nature of the precursor and of the citrate content on the final Pd particle size and catalytic properties of the as-obtained Pd/TiO 2 systems. Characterization was performed using N 2 adsorption-desorption isotherms, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained hybrid Pd/TiO 2 catalysts were tested in the selective hydrogenation (HYD) of an α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Citrate-free Pd/TiO 2-based catalysts present lower selectivity into saturated alcohol. However, citrate-functionalized Pd/TiO 2 catalyst seems to control the selectivity, the particle size and dispersion of Pd NPs leading to high intrinsic activity. © 2011 Elsevier Inc.


Miri B.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Bergaoui L.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Ghorbel A.,Laboratoire Of Chimie Des Materiaux Et Catalyse
Applied Clay Science | Year: 2011

The possibility of substituting aluminum in the Keggin tridecamer [Al13O4(OH)24(H2O)12]7+ by Mn(II) has been investigated and then the obtained polycation has been used as pillars for smectite. Pillaring solutions are prepared by a slow and partial hydrolysis of Al(III)-Mn(II) aqueous solutions with different Mn/(Al+Mn) molar ratio (r=Mn/(Al+Mn)=0, 1/13, 2/13 and 3/13) and examined by 27Al NMR spectroscopy. Powder X-ray diffraction (XRD), physisorption of N2, chemical analysis and scanning electron microscope analyses (SEM) are used to study the precipitated sulfate salts and/or pillared clay minerals. This study reveals the absence of MnAl12 species in the pillaring solution. The crystal system of the obtained Al13-SO4 salt is cubic (tetrahedral particles) in absence of Mn(II) and monoclinic (plate particles) in presence of Mn(II). When r is equal to 3/13, in addition to the monoclinic phase, an amorphous phase takes place.The intercalation process of montmorillonite is only disturbed, when r is equal to 3/13, because of the presence of a high polymeric aluminum phase. © 2011 Elsevier B.V.


Ben Zid T.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Khedher I.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Ghorbel A.,Laboratoire Of Chimie Des Materiaux Et Catalyse
Reaction Kinetics, Mechanisms and Catalysis | Year: 2010

cThe chiral vanadyl salen complexwas immobilized intomesoporous silica by a covalent graftingmethod using 3-aminopropyltriethoxysilane as a reactive surface modifier. The formation and integrity of the complex have been confirmed by FT-IR, UV-vis and BET measurements and the complex was tested in the asymmetric oxidation of sulfide to sulfoxide using H2O2 as oxidant. The immobilized complex showed better catalytic activity than the neat complex, while the neat complex has deactivated in the reaction. The combination of the heterogenized catalyst, H2O2 and CH2Cl2 as solvent offers a selective catalytic system for oxidation of sulfide to sulfoxide with a low but significant enantioselectivity in the range of 8-10% ee. In addition, the heterogenized catalyst could be easily separated from the products and reused. © The Author(s) 2010.


Turki A.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Guillard C.,CNRS Research on Catalysis and Environment in Lyon | Dappozze F.,CNRS Research on Catalysis and Environment in Lyon | Berhault G.,CNRS Research on Catalysis and Environment in Lyon | And 3 more authors.
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2014

1D-TiO2 nanomaterials (nanotubes, nanorods, nanoplates, nanospheres and nanoparticles) with tuned structural and textural properties have been evaluated in the photocatalytic degradation of formic acid (FA) under UV conditions. The FA adsorption isotherms follow the model of Langmuir and the kinetic of FA photodegradation shows Langmuir-Hinshelwood model whatever the TiO2 morphologies. TiO2 nanotubes (HTNT-400), nanoplates (HTNW-700) and nanoparticles (HTNT-500 and HTNT-600) show an interesting photocatalytic activities compared to TiO2 nanospheres (P25) and nanorods (TNR). The nanotubular TiO2 (HTNT-400) has a photocatalytic activity 4 times higher than TiO2 P25. The enhanced activity is attributed to the smaller crystallite size of anatase and tuned surface area of the photocatalyst. The pH study showed that the coexistence of HCOO- and HCOOH species at natural pH (ca. 3.5) is favourable for better adsorption on active sites of titanium oxide nanomaterials and consequently to a better photocatalytic activity. © 2014 Elsevier B.V.


Khedher I.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Ghorbel A.,Laboratoire Of Chimie Des Materiaux Et Catalyse
Journal of Porous Materials | Year: 2010

The heterogeneous Kagan-type catalyst was prepared by an in situ method using MCM-41 as support. The influence of the incorporation process on the structure of MCM-41 was studied using XRD, FT-IR, UV-vis, 29Si-MAS- NMR and N2 adsorption-desorption. The obtained materials showed a definite catalytic activity on the oxidation of sulfide to sulfoxide in the medium containing dichloromethane (solvent) and H2O2 or TBHP (oxidant). © 2009 Springer Science+Business Media, LLC.


Kochkar H.,Center National Of Recherches En Science Des Materiaux Cnrsm | Aouine M.,CNRS Research on Catalysis and Environment in Lyon | Ghorbel A.,Laboratoire Of Chimie Des Materiaux Et Catalyse | Berhault G.,CNRS Research on Catalysis and Environment in Lyon
Journal of Physical Chemistry C | Year: 2011

Shape-controlled silver and palladium nanoparticles were for the first time synthesized by seed-mediated techniques in the presence of β-cyclodextrin (β-CD). Palladium and silver seeds were prepared by reduction of palladium or silver ions with sodium borohydride in the presence of sodium citrate dihydrate as a stabilizer. Seeds were then injected into a "growth" solution containing the same Pd (or Ag) precursor, ascorbic acid (as a weak reducing agent), and β-CD. Using β-cyclodextrin impacts the final morphology of silver nanoparticles through a strong capping effect slowing down the growth regime and shifting it to thermodynamiccontrolled conditions. Adjusting the β-CD/Ag molar ratio can lead to the selective formation of multiply twinned icosahedral particles presenting mainly {111} facets. On palladium, β-cyclodextrin selectively led to the controlled aggregation of primary nanoparticles into nanodendrites or multipods. After deposition on TiO 2, these nanostructured Pd catalysts show excellent activity for the hydrogenation of cinnamaldehyde. © 2011 American Chemical Society.

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