Publications (23)66.9 Total impact
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Article: Infrared study of the influence of reducible iron(III) metal sites on the adsorption of CO, CO2, propane, propene and propyne in the mesoporous metal-organic framework MIL-100.
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ABSTRACT: The present study illustrates the importance of the oxidation state of iron within the mesoporous iron trimesate [{Fe(3)O(H(2)O)(2)F(0.81)(OH)(0.19)}{C(6)H(3)(CO(2))(3)}(2)] denoted MIL-100(Fe) (MIL= Material from Institut Lavoisier) during adsorption of molecules that can interact with the accessible metal sites through π-back donation. Adsorption of CO has been first followed by FTIR spectroscopy to quantify the Lewis acid sites in the dehydrated Fe(III) sample, outgassed at 150 °C, and on the partially reduced Fe(II/III), outgassed at 250 °C. The exposure of MIL-100(Fe) to CO(2), propane, propene and propyne has then been studied by FTIR spectroscopy and microcalorimetry. It appears that π-back donating molecules are strongly adsorbed on reduced iron(II) sites despite the weaker Lewis acidity of cus Fe(2+) sites compared to that of Fe(3+) ones, as shown by pyridine adsorption.Physical Chemistry Chemical Physics 06/2011; 13(24):11748-56. · 3.57 Impact Factor -
Article: Molecular Insight into the Adsorption of H2S in the Flexible MIL-53(Cr) and Rigid MIL-47(V) MOFs: Infrared Spectroscopy Combined to Molecular Simulations
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ABSTRACT: The adsorption of the acid gas H2S has been explored in both MIL-47(V) and MIL-53(Cr) porous metal−organic frameworks (MOFs) by combining infrared measurements and molecular simulations. It is shown that while the MIL-47(V) structure remains rigid upon H2S adsorption up to a pressure of 1.8 MPa, the MIL-53(Cr) solid initially present in the large pore form (LP) switches to its narrow pore version (NP) at very low pressure before undergoing a second structural transition from the NP to the LP versions at higher pressure. Such structural transitions further explain the different shape of the adsorption isotherms for both MILs. A further step consists of providing some insights into the microscopic arrangements of the adsorbate molecules within the pores of the MILs. At the initial stage of adsorption, the H2S molecules mainly form hydrogen bonded species, either as hydrogen donor (in MIL-47 V) or hydrogen-acceptor (in MIL-53Cr) with the μ2-O and μ2-OH groups, respectively, present at the MOF surfaces. At higher pressure (1.8 MPa), the adsorbates are preferentially arranged within the channel in order to form dimers with a high orientational disorder. Both experimental and simulated adsorption enthalpies for H2S decrease in the following sequence: MIL-53(Cr) NP > MIL-47(V) > MIL-53(Cr) LP. The conclusions drawn from this work are then discussed considering the use of such materials for the CH4/H2S separation by means of Pressure Swing Adsorption.01/2011; -
Article: Combined XRD and infrared studies of pyridinium species in (PyH)(3)[PW(12)O(40)] single crystals.
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ABSTRACT: The pyridinium salts of 12-tungstophosphoric acid (PyH)(3)[PW(12)O(40)]·2CH(3)CN (1) and (PyH)(3)[PW(12)O(40)] (2) have been prepared and studied by single crystal and powder X-ray diffraction (XRD) in order to characterize the crystallographic sites occupied by the pyridinium species. The three PyH(+) species are located on two unequivalent sites. Two species are linearly H-bonded to the oxygen atoms of the Keggins unit (α species), whereas the third one (β) forms a bent H-bond. In order to determine the infrared bands characterizing each type of pyridinium species in the 1650-1300 cm(-1) range, infrared spectra have been recorded from room temperature to 100 K. They reveal that only α pyridinium species give rise to the unusual splitting of the PyH(+)ν8b and ν19b modes, whereas β pyridinium species lead to a classical pyridinium spectrum.Physical Chemistry Chemical Physics 10/2010; 13(1):322-7. · 3.57 Impact Factor -
Article: Explanation of the adsorption of polar vapors in the highly flexible metal organic framework MIL-53(Cr).
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ABSTRACT: A comparison of the adsorption of water, methanol, and ethanol polar vapors by the flexible porous chromium(III) terephthalate MIL-53(Cr) was investigated by complementary techniques including adsorption gravimetry, ex situ X-ray powder diffraction, microcalorimetry, thermal analysis, IR spectroscopy, and molecular modeling. The breathing steps observed during adsorption strongly depend on the nature of the vapor. With water, a significant contraction of the framework is observed. For the alcohols, the initial contraction is followed by an expansion of the framework. A combination of IR analysis, X-ray diffraction, and computer modeling leads to the molecular localization of the guest molecules and to the identification of the specific guest-guest and host-guest interactions. The enthalpies of adsorption, measured by microcalorimetry, show that the strength of the interactions decreases from ethanol to water. Differential scanning calorimetry experiments on an EtOH/H(2)O mixture suggest a selective adsorption of ethanol over water.Journal of the American Chemical Society 07/2010; 132(27):9488-98. · 9.91 Impact Factor -
Article: Infrared Investigation of the Acid and Basic Properties of a Sol−Gel Prepared MgF2
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ABSTRACT: This Article reports the use of FTIR spectroscopy of adsorbed probe molecules for the characterization of the acidity and basicity of sol−gel prepared MgF2. The CO adsorption shows that this material possesses 3-, 4- and 5-fold coordinated unsaturated magnesium atoms on the surface. The strength of these Lewis acid sites is medium or weak, but their number is very high (5−6 sites/nm2). Whereas chloroform mainly adsorbs on Lewis acid sites, pyrrole adsorption reveals the presence of weak basic sites which are the first evidence of the basicity of fluorine atoms on the surface of metal fluorites. Both Lewis basic and acidic sites play a role in water adsorption, which is adsorbed on the surface at room temperature.02/2010; -
Article: Functionalization in flexible porous solids: effects on the pore opening and the host-guest interactions.
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ABSTRACT: The synthesis on the gram scale and characterization of a series of flexible functionalized iron terephthalate MIL-53(Fe) type solids are reported. Chemical groups of various polarities, hydrophilicities, and acidities (-Cl, -Br, -CF(3), -CH(3), -NH(2), -OH, -CO(2)H) were introduced through the aromatic linker, to systematically modify the pore surface. X-ray powder diffraction (XRPD), molecular simulations, thermogravimetric analyses, and in situ IR and (57)Fe Mössbauer spectrometries indicate some similarities with the pristine MIL-53(Fe) solid, with the adoption of the narrow pore form for all solids in both the hydrated and dry forms. Combined XRPD and computational structure determinations allow concluding that the geometry of the pore opening is predominantly correlated with the intraframework interactions rather than the steric hindrance of the substituent. Only (MIL-53(Fe)-(CF(3))(2)) exhibits a nitrogen accessible porosity (S(BET) approximately 100 m(2) g(-1)). The adsorption of some liquids leads to pore openings showing some very specific behaviors depending on the guest-MIL-53(Fe) framework interactions, which can be related to the energy difference between the narrow and large pore forms evaluated by molecular simulation.Journal of the American Chemical Society 01/2010; 132(3):1127-36. · 9.91 Impact Factor -
Article: Combined XRD and infrared studies of pyridinium speciesin (PyH)3[PW12O40] single crystals
Physical Chemistry Chemical Physics 01/2010; 12. · 3.57 Impact Factor -
Article: Quantification of water and silanol species on various silicas by coupling IR spectroscopy and in-situ thermogravimetry.
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ABSTRACT: Five silica samples (four precipitated silicas provided by commercial suppliers and one with the MCM-41 structure) have been studied by infrared spectroscopy and by a homemade thermogravimetry-infrared spectrum (TG-IR) setup. The silanol amount, accessibility to water, and different alcohols, and the affinity to water of these various silicas were compared and quantified. TG-IR measurements allowed the precise determination of the integrated molar absorption coefficient of the (nu+delta)OH band, epsilon(nu+delta)OH=(0.16+/-0.01) cm micromol(-1). It is independent of the sample origin and the concentration of silanol groups on silicas. For the precipitated dried samples evacuated at room temperature, the silanol concentration COH varies between 3.6 and 7.0 mmol g(-1). It is 5.3 mmol g(-1) in the case of the MCM-41 sample. Exchange experiments with D2O, followed by back-exchanges with different alcohols (methanol, propan-2-ol, 2-methyl-propan-2-ol, and 3-ethyl-pentan-3-ol) have been followed by infrared spectroscopy. All of the silanols of the MCM-41 sample are accessible to water and alcohol molecules. By contrast, about 20% of the silanols in precipitated samples are not exchanged by D2O (internal silanols). Accessibility decreases with alcohol size; the main effect is relative to methanol. Taking into account the sample specific surface areas and the silanol accessibility to D2O, the surface silanol density of precipitated silicas is close to 8 OH per nm2, at maximum coverage. At variance, the silanol surface density of the MCM silica is much lower, 4 OH per nm2. The TG-IR setup has also been used to determine the amount of water adsorbed on silicas through the intensity of the deltaH2O band. It varies linearly with the concentration of adsorbed water, whatever the silica sample. The integrated molar absorption coefficient of two bands, epsilondeltaH2O=(1.53+/-0.03) cm micromol(-1) and epsilon(nu+delta)H2O=(0.22+/-0.01) cm micromol(-1), have been determined. The number of H2O molecules adsorbed per nm2 has been compared on the five samples under an equilibrium pressure of 13 hPa at room temperature. Taking into account the number of silanols accessible to D2O for each sample, the silica-water affinity has been defined by the H2O/(SiOHsurf) ratio. It is close to 0.8-0.9 for the precipitated samples but lower (0.7) in the case of the MCM one. This result is explained by the more important amount of isolated silanol groups presented by this sample.Langmuir 06/2009; 25(10):5825-34. · 4.19 Impact Factor -
Article: The use of multiple probe molecules for the study of the acid-base properties of aluminium hydroxyfluoride having the hexagonal tungsten bronze structure: FTIR and [36Cl] radiotracer studies.
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ABSTRACT: The combination of several probe molecules has enabled the construction of a detailed picture of the surface of aluminium hydroxyl fluoride, AlF(2.6)(OH)(0.4), which has the hexagonal tungsten bronze (HTB) structure. Using pyridine as a probe leads to features at 1628 cm(-1), ascribed to very strong Lewis acid sites, and at 1620-1623 cm(-1), which is the result of several different types of Lewis sites. This heterogeneity is indicated also from CO adsorption at 100 K; the presence of five different types of Lewis site is deduced and is suggested to arise from the hydroxylated environment. Brønsted acid sites of medium strength are indicated by adsorption of lutidine and CO. Adsorption of lutidine occurs at OH groups, which are exposed at the surface and CO reveals that these OH groups have a single environment that can be correlated with their specific location inside the bulk, assuming that the surface OH group may reflect the bulk OH periodicity. A correlation between the data obtained from CO and pyridine molecules has been established using co-adsorption experiments, which also highlight the inductive effect produced by pyridine. Adsorption of the strong Brønsted acid, anhydrous hydrogen chloride, detected by monitoring the beta(-) emission of [(36)Cl]-HCl at the surface, indicates that surface hydroxyl groups can behave also as a Brønsted base and that H(2)O-HCl interactions, either within the hexagonal channels or at the surface are possible. Finally, the formation of strongly bound H(36)Cl as a result of the room temperature dehydrochlorination of [(36)Cl]-labelled tert-butyl chloride provides additional evidence that HTB-AlF(2.6)(OH)(0.4) can behave as a Lewis acid.Physical Chemistry Chemical Physics 04/2009; 11(9):1369-79. · 3.57 Impact Factor -
Article: Coupling sol-gel synthesis and microwave-assisted techniques: a new route from amorphous to crystalline high-surface-area aluminium fluoride.
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ABSTRACT: A non-aqueous sol-gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 degrees C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 degrees C) the metastable form beta-AlF3 was obtained with a very large surface area of 125 m2 g(-1). The mechanism of the amorphous=crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 degrees C) a multi-component material mixture exhibiting a huge surface area of 525 m2 g(-1) has been obtained and further investigated after mild post-treatment fluorination using F2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m2 g(-1). HRTEM revealed that the solid is built from large particles (50 nm) identified as alpha-AlF3, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.Chemistry 02/2008; 14(20):6205-12. · 5.93 Impact Factor -
Article: Evidence of CO(2) molecule acting as an electron acceptor on a nanoporous metal-organic-framework MIL-53 or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2)).
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ABSTRACT: The adsorption mode of CO(2) at low coverage in the nanoporous metal benzenedicarboxylate MIL-53(Cr) or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2)) has been identified using IR spectroscopy; the red shift of the nu(3) band and the splitting of the nu(2) mode of CO(2) in addition to the shifts of the nu(OH) and delta(OH) bands of the MIL-53(Cr) hydroxyl groups provide evidence that CO(2) interacts with the oxygen atoms of framework OH groups as an electron-acceptor via its carbon atom; this is the first example of such an interaction between CO(2) and bridged OH groups in a solid.Chemical Communications 09/2007; · 6.17 Impact Factor -
Article: Creation of Controlled Brønsted Acidity on a Zeotypic Mesoporous Chromium(III) Carboxylate by Grafting Water and Alcohol Molecules
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ABSTRACT: This paper reports a new way of modulating the strength of the Brønsted acid sites of a porous solid. Our approach consists of the grafting of various polar molecules (H2O, CD3OH, CF3CH2OH, and (CF3)2CHOH) on MIL-100(Cr), a mesoporous crystallized chromium carboxylate with accessible unsaturated metal sites. We demonstrate, using infrared spectroscopy, that all these compounds do coordinate on the coordinatively unsaturated Cr3+ sites. This generates controlled Brønsted acid sites whose strength, measured by CO adsorption at 100 K, depends on the nature of the adsorbate. It can vary from H0 = −3 (CD3OH) to −8 ((CF3)2CHOH).11/2006; -
Article: Investigation of acid sites in a zeotypic giant pores chromium(III) carboxylate.
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ABSTRACT: A study of the zeotypic giant pores chromium(III) tricarboxylate Cr(III)3OF(x)(OH)(1-x)(H2O)2 x {C6H3-(CO2)3}2 x nH2O (MIL-100) has been performed. First, its thermal behavior, studied by X-ray thermodiffractometry and infrared spectroscopy, indicates that the departure of water occurs without any pore contraction and no loss in crystallinity, which confirms the robustness of the framework. In a second step, IR spectroscopy has shown the presence of three distinct types of hydroxy groups depending on the outgassing conditions; first, at high temperatures (573 K), only Cr-OH groups with a medium Brønsted acidity are present; at lower temperatures, two types of Cr-H2O terminal groups are observed; and at room temperature, their relatively high Brønsted acidity allows them to combine with H-bonded water molecules. Finally, a CO sorption study has revealed that at least three Lewis acid sites are present in MIL-100 and that fluorine atoms are located on a terminal position on the trimers of octahedra. A first result of grafting of methanol molecules acting as basic organic molecules on the chromium sites has also been shown, opening the way for a postsynthesis functionalization of MIL-100.Journal of the American Chemical Society 04/2006; 128(10):3218-27. · 9.91 Impact Factor -
Article: An example of misinterpretation of IR spectra of adsorbed species due to gas phase H 2 O: Comment on "The surface acidity and characterization of Fe-montmorillonite probed by in situ FT-IR spectroscopy of adsorbed pyridine" [Appl. Catal. A 294 (2005) 156-160]
Applied Catalysis A: General. 01/2006; 302(2):333-334. -
Article: Relationship between infrared spectra and stoichiometry of pyridine-H 3 PW 12 O 40 salts using a new TGA-infrared coupling
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ABSTRACT: A new thermogravimetric-infrared coupled apparatus was used to determine the stoichiometry of the pyridinium salts resulting from absorption of pyridine on H3PW12O40 (HPW). Gravimetric measurements showed that two pyridinium salts with definite stoichiometry--(Py2H+)3PW12O40 (bis-pyridinium salt) and (PyH+)3PW12O40 (mono-pyridinium salt)--are formed. Their infrared spectra closely correspond to those reported for pyridinium salts in strong acid solutions. The splitting of the [nu]8b and [nu]19b bands of absorbed pyridine (1610-1603 cm-1 and 1540-1532 cm-1, respectively) is characteristic of mono-pyridinium formation in the HPW structure.Journal of Catalysis. 01/2006; 241(1):221-224. -
Article: 2,6-dimethylpyridine as a probe of the strength of Brønsted acid sites: study on zeolites. Application to alumina.
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ABSTRACT: The positions of nu8a and nu*(NH) bands in the spectrum of protonated 2,6-dimethylpyridine vary with the strength of Brønsted acidity: the higher the nu*(NH) wavenumber and the lower the nu8a wavenumber, the stronger the acidity. The results obtained with 2,6-dimethylpyridine adsorption correlate with those obtained by CO adsorption experiments on a series of faujasite zeolites (LiHNaY, KHNaY, HY, HY(SA), HNaX). These relations were extended to gamma-Al2O3 having weak Brønsted acidity, not detected by pyridine and hardly detected by CO. The number (0.1 per nm2) and the strength (corresponding to delta nu (OH) by CO = 155 cm(-1)) of the most acidic OH groups of Al2O3, as well as the position of the corresponding nu (OH) band (<3700 cm(-1)) are deduced from 2,6-dimethylpyridine adsorption experiments.Physical Chemistry Chemical Physics 04/2005; 7(8):1861-9. · 3.57 Impact Factor -
Article: FT-IR study of the adsorption and transformation of formaldehyde on oxide surfaces
04/2002; -
Article: Microcalorimetric and FT-IR spectroscopic study of the adsorption of isopropyl alcohol and hexafluoroisopropyl alcohol on titanium dioxide
04/2002; -
Article: Microcalorimetric and Fourier transform infrared spectroscopic studies of methanol adsorption on alumina
04/2002; -
Article: A Spectroscopic Characterization of the Reduction of Ceria from Electronic Transitions of Intrinsic Point Defects
04/2002;
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2010
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Aix-Marseille Université
Marseille, Provence-Alpes-Cote d'Azur, France -
Université de Versailles Saint-Quentin
Versailles, Ile-de-France, France
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