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Personne :
Kleitz, Freddy

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Kleitz

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Freddy

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Département de chimie, Faculté des sciences et de génie, Université Laval

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ncf11860447

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Voici les éléments 1 - 10 sur 11
  • PublicationAccès libre
    Carbon dioxide oversolubility in nanoconfined liquids for the synthesis of cyclic carbonates
    (Wiley, 2017-02-10) Fontaine, Frédéric-Georges; Zakharova, Maria; Kleitz, Freddy
    The physical phenomenon of gas oversolubility in nanoconfined liquids was successfully applied for the catalytic cycloaddition of carbon dioxide to epoxides to generate organic cyclic carbonates. Hybrid adsorbents based on MCM‐41 and SBA‐15 mesoporous silica materials were synthesized, and efficient nucleophile deposition on the surface of the support was achieved through a grafting procedure, which allowed for an effective and durable metal‐free catalytic system. Room‐temperature transformation of styrene and hexene oxides to the corresponding organic carbonates at atmospheric pressure of carbon dioxide was explored.
  • PublicationAccès libre
    Substantiating the influence of pore surface functionalities on the stability of grubbs catalyst in mesoporous SBA-15 silica
    (VCH Verlagsgesellschaft/Verla, 2011-03-08) Fontaine, Frédéric-Georges; Kleitz, Freddy; Staub, Hélène; Kayser, Laure; Even, Nicolas; Guillet-Nicolas, Rémy
    The influence of pore surface functionalities in mesoporous SBA‐15 silica on the stability of a model olefin metathesis catalyst, namely Grubbs I, is substantiated. In particular, it is demonstrated that the nature of the interaction between the ruthenium complex and the surface is strongly depending on the presence of surface silanols. For this study, differently functionalized mesoporous SBA‐15 silica materials were synthesized according to standard procedures and, subsequently, the Grubbs I catalyst was incorporated into these different host materials. All of the materials were thoroughly characterized by elemental analyses, nitrogen physisorption at −196 °C, thermogravimetric analyses, solid‐state NMR spectroscopy, and infrared spectroscopy (ATR‐IR). By such in‐depth characterization of the materials, it became possible to achieve models for the surface/catalyst interactions as a function of surface functionalities in SBA‐15; for example, in the case of purely siliceous silanol‐rich SBA‐15, octenyl‐silane modified SBA‐15, and silylated equivalents. It was evidenced that large portions of the chemisorbed species that are detected spectroscopically arise from interactions between the tricyclohexylphosphine and the surface silanols. A catalytic study using diethyldiallylmalonate in presence of the various functionalized silicas shows that the presence of surface silanols significantly decreases the longevity of the ring‐closing metathesis catalyst, whereas the passivation of the surface by trimethylsilyl groups slows down the catalysis rate, but does not affect significantly the lifetime of the catalyst. This contribution thus provides new insights into the functionalization of SBA‐15 materials and the role of surface interactions for the grafting of organometallic complexes.
  • PublicationAccès libre
    Lewis acidity quantification and catalytic activity of Ti, Zr and Al-supported mesoporous silica
    (Royal Society of Chemistry, 2017-02-14) Fontaine, Frédéric-Georges; Zakharova, Maria; Kleitz, Freddy
    Water-tolerant supported Lewis acids are actively sought after, in particular to address the challenging direct amidation reaction. To this aim, a versatile and easy synthesis of large pore silica materials with supported Ti-, Al-, Zr-Lewis acids, using acetyl acetonate as a metal-stabilizing agent, was accomplished. The formation of bulk metal oxides was not observed, even at high concentrations of metal species. The Lewis acidity was demonstrated using quantitative and qualitative titration techniques using a series of Hammett indicators, such as butter yellow, phenylazodiphenylphosphine and dicinnamalacetone. The optimal concentration of metals corresponding to the highest Lewis acidity of solids was found to be 4% for Al-SBA-15, 12–15% for Ti-SBA-15 and 7% for Zr-SBA-15 materials. The water-tolerance of the supported metal centers was explored by a pyridine adsorption-FTIR study before and after water addition. The metalated materials were used as water-tolerant heterogeneous catalysts for the amidation of electron-poor and bulky amines, such as substituted anilines and morpholine, obtaining 59–99% yield of the corresponding amides.
  • PublicationAccès libre
    Confinement of the Grubbs catalyst in alkene-functionalized mesoporous silica
    (Elsevier BV, 2013-03-15) Fontaine, Frédéric-Georges; Kleitz, Freddy; Staub, Hélène
    Herein, we report on the impact of alkyl chain length of olefin moieties anchored into silica mesopores on the confinement behavior and stability of the first-generation Grubbs catalyst, i.e., [RuCl2(C(H)(Ph))(PCy3)2] . In this contribution, ordered mesoporous SBA-15 silica materials were functionalized with alkenyl-trichlorosilanes exhibiting different carbon chain lengths, e.g., vinyl- (C2), allyl- (C3), hexenyl- (C6) and octenyl- (C8) trichlorosilanes. Subsequently, the Grubbs I catalyst was incorporated into these different host materials in the presence of organic solvent. The thus-obtained materials, before and after interaction with Grubbs I, were characterized by a variety of methods, including N2 physisorption, thermogravimetric analyses, solid state NMR (13C, 31P and 29Si) and attenuated total reflectance (ATR) infra-red spectroscopy. Our investigations reveal a pronounced dependence of the Grubbs surface stability as a function of the grafted alkyl chain length of the alkene moieties. The nature of the immobilized Ru-based species is function of the surface modification and the presence of residual silanol groups.
  • PublicationAccès libre
    Highly efficient and selective recovery of rare earth elements using mesoporous silica functionalized by preorganized chelating ligands
    (American Chemical Society, 2017-10-02) Drouin, Élisabeth; Fontaine, Frédéric-Georges; Larivière, Dominic; Kleitz, Freddy; Hu, Yimu
    Separating the rare earth elements (REEs) in an economically and environmentally sustainable manner is one of the most pressing technological issues of our time. Herein, a series of preorganized bidentate phthaloyl diamide (PA) ligands was synthesized and grafted on large-pore 3-dimensional (3-D) KIT-6 mesoporous silica. The synthesized sorbents were fully characterized by N2 physisorption, FT-IR, 13C cross-polarization (CP) and 29Si magic-angle spinning (MAS) NMR, thermogravimetric analysis-differential thermal analysis (TGA-DTA), and elemental analysis. Overall, the grafting of PA-type ligands was found to have significantly improved the extraction performance of the sorbents toward REEs compared to the homogeneous analogues. Specifically, the sorbent modified with the 1,2-phtaloyl ligand shows high preference over lanthanides with smaller size, whereas the 1,3-phtaloyl ligand exhibits selectivity toward elements with larger ion radius. This selectivity drastically changes from the homogeneous models that do not exhibit any selectivity. The possibility of regenerating the mesoporous sorbents through simple stripping using oxalate salt is demonstrated over up to 10 cycles with no significant loss in REEs extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials. Despite the complex ion matrix and high ionic composition, the exposure of industrial mining deposits containing REEs to the sorbents results in selective recovery of target REEs.
  • PublicationAccès libre
    Recent advances in the separation of rare earth elements using Mesoporous hybrid materials
    (Wiley, 2018-05-27) Fontaine, Frédéric-Georges; Larivière, Dominic; Kleitz, Freddy; Hu, Yimu
    Over the past decades, the need for rare earth elements (REEs) has increased substantially, mostly because these elements are used as valuable additives in advanced technologies. However, the difference in ionic radius between neighboring REEs is small, which renders an efficient sized‐based separation extremely challenging. Among different types of extraction methods, solid‐phase extraction (SPE) is a promising candidate, featuring high enrichment factor, rapid adsorption kinetics, reduced solvent consumption and minimized waste generation. The great challenge remains yet to develop highly efficient and selective adsorbents for this process. In this regard, ordered mesoporous materials (OMMs) possess high specific surface area, tunable pore size, large pore volume, as well as stable and interconnected frameworks with active pore surfaces for functionalization. Such features meet the requirements for enhanced adsorbents, not only providing huge reactional interface and large surface capable of accommodating guest species, but also enabling the possibility of ion‐specific binding for enrichment and separation purposes. This short personal account summarizes some of the recent advances in the use of porous hybrid materials as selective sorbents for REE separation and purification, with particular attention devoted to ordered mesoporous silica and carbon‐based sorbents.
  • PublicationAccès libre
    Iron-modified mesoporous silica as efficient solid lewis acid catalyst for the mukaiyama aldol reaction
    (American Chemical Society, 2018-01-08) Ollevier, Thierry; Kleitz, Freddy; Xu, Wan
    Fe-MCM-41 and Fe-SBA-15, two different iron-containing mesoporous silicas, were successfully synthesized by a straightforward and versatile method using iron acetylacetonate as a metal precursor. pH adjustment with ammonia during the synthesis was found to be an efficient way to improve the iron content. Physicochemical parameters of the iron-containing mesoporous silicas were obtained by nitrogen physisorption measurements, and the coordination environment of iron elements was validated by UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The surface acidity was tested by using a series of Hammett indicators. To further distinguish the Lewis acid sites on the surface, a pyridine adsorption FT-IR method was implemented. These prepared nanoporous catalysts were screened in the Mukaiyama aldol reaction as a model reaction catalyzed by a Lewis acid. The Lewis acid catalytic activity of the materials was fine-tuned, and the corresponding aldol products were obtained in good yield and selectivity. More importantly, the solid catalysts were very stable and could be reused at least nine times while maintaining the same catalytic activity.
  • PublicationRestreint
    A microfluidic approach to micromembrane synthesis for complex release profiles of nanocarriers
    (Royal Society of Chemistry, 2020-02-14) Nan, Jia; Greener, Jesse; Rosella, Erica; Kleitz, Freddy; Juère, Estelle; Pouliot, Roxane
    Physically crosslinked microscale biomembranes synthesized from pure chitosan are designed and demonstrated for pH-triggered release of embedded functionalized mesoporous silica nanoparticles. Nanoparticle-loaded membranes are formed in a microfluidic channel at the junction between accurately controlled co-flowing streams to achieve highly tuneable membrane properties. After formation, the loaded membranes remain stable until contact with physiological acidic conditions, resulting in controlled nanoparticle release. Furthermore, nanoparticle-loaded membranes with complex layered architectures are synthesized using different flow schemes, thus enabling customized nanoparticle release profiles. These novel materials are well-suited for integration within small medical devices as well as off-chip applications.
  • PublicationAccès libre
    Selective separation and preconcentration of Th(IV) using organo-functionalized, hierarchically porous silica monoliths
    (Royal Society of Chemistry (Great Britain), 2018-11-26) Giret, Simon; Fontaine, Frédéric-Georges; Meinusch, Rafael; Larivière, Dominic; Han, Jongho; Kleitz, Freddy; Hu, Yimu
    The potential application of thorium (Th) as nuclear fuel, as well as the environmental and public health concerns associated with it, promotes the development of economic and sustainable materials for the separation and removal of Th(IV) from minerals and environmental samples. In this work, centimeter-size, porous silica monoliths exhibiting hierarchical macroporosity–mesoporosity and a robust silica skeleton were prepared using a sol–gel process combined with post-synthetic hydrothermal treatment in ammonium hydroxide. Upon functionalization with diglycolamide (DGA), the resulting monolithic hybrid material was used as a column-type fixed bed sorbent for continuous flow extraction. An enhanced Th(IV) uptake from aqueous solution was achieved with a high enrichment factor and selectivity in the presence of competitive ions such as rare earth elements (REEs) and uranium (U). Systematic mechanistic studies show that the hierarchical pore system is crucial for enhanced adsorption kinetics and capacity. Two mineral leachates were used to assess the performances of the hybrid material, and despite the complex ion matrix and high ionic composition, the sorbent shows highly efficient recovery of Th(IV). The material was able to undergo 10 extraction–stripping–regeneration cycles, which bodes well for potential industrial applications.
  • PublicationAccès libre
    Selective recovery of rare earth elements using chelating ligands grafted on mesoporous surfaces
    (Royal Society of Chemistry, 2015-11-25) Mushtaq, Ambreen; Fontaine, Frédéric-Georges; Larivière, Dominic; Florek, Justyna Agata; Cantin, Gabrielle; Kleitz, Freddy
    Nowadays, rare earth elements (REEs) and their compounds are critical for the rapidly growing advanced technology sectors and clean energy demands. However, their separation and purification still remain challenging. Among different extracting agents used for REE separation, the diglycolamide (DGA)-based materials have attracted increasing attention as one of the most effective extracting agents. In this contribution, a series of new and element-selective sorbents were generated through derivatisation of the diglycolamide ligand (DGA), grafted to mesoporous silica and tested for the separation of rare earth elements. It is shown that, by tuning the ligand bite angle and its environment, it is possible to improve the selectivity towards specific rare earth elements.