232 research outputs found
Functionalized nanodiamond as potential synergist in flame-retardant ethylene vinyl acetate
International audiencePristine and phosphorylated detonation nanodiamonds (ND) were incorporated in ethylene vinyl acetate (EVA)as potential synergist agents to improve flame retardancy. Combinations of 5 wt% of pristine or modified ND and20 or 25 wt% of Ammonium Polyphosphate (APP) were investigated using ThermoGravimetric Analysis (TGA),Pyrolysis Combustion Flow Calorimeter (PCFC), and Cone Calorimeter (CC). The study of thermal stability showsthat APP and pure ND interacts, resulting in the formation of a char residue which is stable up to 750 °C. A strongreduction in the peak of HRR at Cone Calorimeter is highlighted for APP/ND combinations. PCFC data show thatthe peak of heat release rate (pHRR) decreases with the additive content. All these experiments suggest theformation of a thick charring layer, able to protect the material during thermal degradation. SEM micrographsconfirm that EVA/APP/ND residues are more cohesive than EVA/APP ones
Dehydration of Alginic Acid Cryogel by TiCl4 vapor : Direct Access to Mesoporous TiO2@C Nanocomposites and Their Performance in Lithium-Ion Batteries
A new strategy for the synthesis of mesoporous TiO2@C nanocomposites through the direct mineralization of seaweed-derived alginic acid cryogel by TiCl4 through a solid/vapor reaction pathway is presented. In this synthesis, alginic acid cryogel can have multiple roles; i) mesoporous template, ii) carbon source, and iii) oxygen source for the TiO2 precursor, TiCl4. The resulting TiO2@alginic acid composite was transformed either into pure mesoporous TiO2 by calcination or into mesoporous TiO2@C nanocomposites by pyrolysis. By comparing with a nonporous TiO2@C composite, the importance of the mesopores on the performance of electrodes for lithium-ion batteries based on mesoporous TiO2@C composite was clearly evidenced. In addition, the carbon matrix in the mesoporous TiO2@C nanocomposite also showed electrochemical activity versus lithium ions, providing twice the capacity of pure mesoporous TiO2 or alginic acid-derived mesoporous carbon (A600). Given the simplicity and environmental friendliness of the process, the mesoporous TiO2@C nanocomposite could satisfy the main prerequisites of green and sustainable chemistry while showing improved electrochemical performance as a negative electrode for lithium-ion batteries
EURYDICE : A platform for unified access to documents
rédigé le 14 octobre 2001In this paper we present Eurydice, a platform dedicated to provide a unified gateway to documents. Its basic functionalities about collecting documents have been designed based on a long experience about the management of scientific documentation among large and demanding academic communities such as IMAG and INRIA. Besides the basic problem of accessing documents - which was of course the original and main motivation of the project - a great effort has been dedicated to the development of management functionalities which could help institutions to control, analyse the current situation about the use of the documentation, and finally to set a better ground for a documentation policy. Finally a great emphasis - and corresponding technical investment - has been put on the protection of property and reproduction rights both from the users' intitution side and from the editors' side
Proton conductivity versus acidic strength of one-pot synthesized acidic functionalized SBA-15 Mesoporous silica
International audienceThis paper reports the one-pot synthesis and characterization of functionalized mesoporous SBA-15 silica, containing two loadings of different acid groups (-CO2H, -PO(OH)2 and -SO3H). The thermodynamic features of the water confined in these porous silicas is investigated by Differential Scanning Calorimetry (DSC). The results show that the melting behaviour of the confined water is mainly governed by the pore diameter and, as a consequence, indicate that the chemical "decoration" of the porous surface does not play any key role on water thermodynamics in that case. On the contrary, the proton conductivity of the hydrated mesoporous materials, examined in a wide range of temperatures (-100 to 70°C), turns out to be strongly dependent on both the physical state of the confined water and the acidity of the functions located at the porous surface. The proton conductivity is shown to be directly related to the pKa and the density of the functional groups attached to the mesopore surface. The high conductivity values obtained at low temperature when the confined water is frozen, let us think that the -SO3H functionalized SBA-15 investigated here could be promising candidates for electrolyte solids applications in fuel cells
Alginic acid-derived mesoporous carbonaceous materials (StarbonÂź) as negative electrodes for lithium ion batteries : Importance of porosity and electronic conductivity
Alginic acid-derived mesoporous carbonaceous materials (StarbonÂź A800 series) were investigated as negative electrodes for lithium ion batteries. To this extent, a set of mesoporous carbons with different pore volume and electronic conductivity was tested. The best electrochemical performance was obtained for A800 with High Pore Volume (A800HPV), which displays both the highest pore volume (0.9 cm3 gâ1) and the highest electronic conductivity (84 S mâ1) of the tested materials. When compared to a commercial mesoporous carbon, A800HPV was found to exhibit both better long-term stability, and a markedly improved rate capability. The presence of a hierarchical interconnected pore network in A800HPV, accounting for a high electrolyte accessibility, could lay at the origin of the good electrochemical performance. Overall, the electronic conductivity and the mesopore size appear to be the most important parameters, much more than the specific surface area. Finally, A800HPV electrodes display similar electrochemical performance when formulated with or without added conductive additive, which could make for a simpler and more eco-friendly electrode processing
Sustainable polysaccharide-derived mesoporous carbons (StarbonÂź) as additives in lithium-ion batteries negative electrodes
For the first time, polysaccharide-derived mesoporous carbonaceous materials (StarbonÂź) are used as carbon additives in Li-ion battery negative electrodes. A set of samples with pore volumes ranging from â0 to 0.91 cm3 g-1 was prepared to evidence the role of porosity in such sustainable carbon additives. Both pore volume and pore diameter have been found crucial parameters for improving the electrodes performance e.g. reversible capacity. Mesoporous carbons with large pore volumes and pore diameters provide efficient pathways for both lithium ions and electrons as proven by the improved electrochemical performances of Li4Ti5O12 (LTO) and TiO2 based electrodes compared to conventional carbon additives. The mesopores provide easy access for the electrolyte to the active material surface, and the fibrous morphology favors the connection of active materials particles. These results suggest that polysaccharide-derived mesoporous carbonaceous materials are promising, sustainable carbon additives for Li-ion batteries
One-pot synthesis of hierarchical porous layered hybrid materials based on aluminosilicate sheets and organic functional pillars
Layered hybrid materials (LHMs) based on ordered silicoaluminate sheets linked with organic fragments, perpendicularly located and stabilized in the interlayer space, were synthesized by a one-pot direct hydrothermal process in the absence of structural directing agents (SDAs) and using bridged silsesquioxanes as organosilicon precursors. By following the synthesis described here, the preliminary preparation of inorganic layered precursors, post-synthesis swelling and/or pillaring treatments can be avoided. The physico-chemical and structural characteristics of the materials were studied by chemical and thermogravimetrical analyses, X-ray diffraction, TEM microscopy, spectroscopic techniques (NMR and FTIR) and textural measurements. The complete exchange of intracrystalline sodium cations by protons, without substantial structural alteration of the hybrid materials, facilitated the generation of hybrid materials, which contained acid and base sites located in the inorganic (silicoaluminate layers) and in the organic interlayer linkers, respectively, with the resultant acid base materials showing promise as active and selective catalysts.The authors thank financial support to Spanish Government by Consolider-Ingenio MULTICAT CSD2009-00050, MAT2011-29020-C02-01 and Severo Ochoa Excellence Program SEV-2012-0267. AG and JMM thank pre-doctoral fellowships from MINECO for economical support.Gaona Cordero, A.; Moreno, JM.; Velty, A.; DĂaz Morales, UM.; Corma CanĂłs, A. (2014). One-pot synthesis of hierarchical porous layered hybrid materials based on aluminosilicate sheets and organic functional pillars. Journal of Materials Chemistry A. 2(45):19360-19375. https://doi.org/10.1039/c4ta04742gS1936019375245Fontecave, T., Sanchez, C., AzaĂŻs, T., & BoissiĂšre, C. (2012). Chemical Modification As a Versatile Tool for Tuning Stability of Silica Based Mesoporous Carriers in Biologically Relevant Conditions. Chemistry of Materials, 24(22), 4326-4336. doi:10.1021/cm302142kDrisko, G. L., & Sanchez, C. (2012). Hybridization in Materials Science - Evolution, Current State, and Future Aspirations. European Journal of Inorganic Chemistry, 2012(32), 5097-5105. doi:10.1002/ejic.201201216Nicole, L., Laberty-Robert, C., Rozes, L., & Sanchez, C. (2014). Hybrid materials science: a promised land for the integrative design of multifunctional materials. Nanoscale, 6(12), 6267-6292. doi:10.1039/c4nr01788aWight, A. P., & Davis, M. E. (2002). Design and Preparation of OrganicâInorganic Hybrid Catalysts. Chemical Reviews, 102(10), 3589-3614. doi:10.1021/cr010334mFĂ©rey, G. (2008). Hybrid porous solids: past, present, future. Chem. Soc. Rev., 37(1), 191-214. doi:10.1039/b618320bHoffmann, F., Cornelius, M., Morell, J., & Fröba, M. (2006). Silica-Based Mesoporous OrganicâInorganic Hybrid Materials. Angewandte Chemie International Edition, 45(20), 3216-3251. doi:10.1002/anie.200503075Sanchez, C., Boissiere, C., Cassaignon, S., Chaneac, C., Durupthy, O., Faustini, M., ⊠Sassoye, C. (2013). Molecular Engineering of Functional Inorganic and Hybrid Materials. Chemistry of Materials, 26(1), 221-238. doi:10.1021/cm402528bSanchez, C., JuliĂĄn, B., Belleville, P., & Popall, M. (2005). Applications of hybrid organicâinorganic nanocomposites. Journal of Materials Chemistry, 15(35-36), 3559. doi:10.1039/b509097kInagaki, S., Guan, S., Ohsuna, T., & Terasaki, O. (2002). An ordered mesoporous organosilica hybrid material with a crystal-like wall structure. Nature, 416(6878), 304-307. doi:10.1038/416304aCorma, A., GarciÌa, H., & LlabreÌs i Xamena, F. X. (2010). Engineering Metal Organic Frameworks for Heterogeneous Catalysis. Chemical Reviews, 110(8), 4606-4655. doi:10.1021/cr9003924Reale, E., Leyva, A., Corma, A., MartĂnez, C., GarcĂa, H., & Rey, F. (2005). A fluoride-catalyzed solâgel route to catalytically active non-ordered mesoporous silica materials in the absence of surfactants. Journal of Materials Chemistry, 15(17), 1742. doi:10.1039/b415066jLi, H., Eddaoudi, M., OâKeeffe, M., & Yaghi, O. M. (1999). Design and synthesis of an exceptionally stable and highly porous metal-organic framework. Nature, 402(6759), 276-279. doi:10.1038/46248Ruiz-Hitzky, E., Darder, M., & Aranda, P. (2005). Functional biopolymer nanocomposites based on layered solids. Journal of Materials Chemistry, 15(35-36), 3650. doi:10.1039/b505640nLeonowicz, M. E., Lawton, J. A., Lawton, S. L., & Rubin, M. K. (1994). MCM-22: A Molecular Sieve with Two Independent Multidimensional Channel Systems. Science, 264(5167), 1910-1913. doi:10.1126/science.264.5167.1910Lagaly, G. (1986). Interaction of alkylamines with different types of layered compounds. Solid State Ionics, 22(1), 43-51. doi:10.1016/0167-2738(86)90057-3Corma, A., Corell, C., PĂ©rez-Pariente, J., Guil, J. M., Guil-LĂłpez, R., Nicolopoulos, S., ⊠Vallet-Regi, M. (1996). Adsorption and catalytic properties of MCM-22: The influence of zeolite structure. Zeolites, 16(1), 7-14. doi:10.1016/0144-2449(95)00084-4Occelli, M. L. (1983). Physicochemical Properties of Montmorillonite Interlayered with Cationic Oxyaluminum Pillars. Clays and Clay Minerals, 31(1), 22-28. doi:10.1346/ccmn.1983.0310104Srivastava, V., Gaubert, K., Pucheault, M., & Vaultier, M. (2009). Organic-Inorganic Hybrid Materials for Enantioselective Organocatalysis. ChemCatChem, 1(1), 94-98. doi:10.1002/cctc.200900035Motokura, K., Tada, M., & Iwasawa, Y. (2009). Layered Materials with Coexisting Acidic and Basic Sites for Catalytic One-Pot Reaction Sequences. Journal of the American Chemical Society, 131(23), 7944-7945. doi:10.1021/ja9012003BaleizĂŁo, C., Gigante, B., Sabater, M. J., Garcia, H., & Corma, A. (2002). On the activity of chiral chromium salen complexes covalently bound to solid silicates for the enantioselective epoxide ring opening. Applied Catalysis A: General, 228(1-2), 279-288. doi:10.1016/s0926-860x(01)00979-6Ayala, V., Corma, A., Iglesias, M., RincĂłn, J. A., & SĂĄnchez, F. (2004). Hybrid organicâinorganic catalysts: a cooperative effect between support, and palladium and nickel salen complexes on catalytic hydrogenation of imines. Journal of Catalysis, 224(1), 170-177. doi:10.1016/j.jcat.2004.02.017Corma, A., Fornes, V., & Rey, F. (2002). Delaminated Zeolites: An Efficient Support for Enzymes. Advanced Materials, 14(1), 71-74. doi:10.1002/1521-4095(20020104)14:13.0.co;2-wIshii, R., Ikeda, T., Itoh, T., Ebina, T., Yokoyama, T., Hanaoka, T., & Mizukami, F. (2006). Synthesis of new microporous layered organicâinorganic hybrid nanocomposites by alkoxysilylation of a crystalline layered silicate, ilerite. J. Mater. Chem., 16(41), 4035-4043. doi:10.1039/b610088kMochizuki, D., Kowata, S., & Kuroda, K. (2006). Synthesis of Microporous InorganicâOrganic Hybrids from Layered Octosilicate by Silylation with 1,4-Bis(trichloro- and dichloromethyl-silyl)benzenes. Chemistry of Materials, 18(22), 5223-5229. doi:10.1021/cm061357qCorma, A., DiÌaz, U., GarciÌa, T., Sastre, G., & Velty, A. (2010). Multifunctional Hybrid OrganicâInorganic Catalytic Materials with a Hierarchical System of Well-Defined Micro- and Mesopores. Journal of the American Chemical Society, 132(42), 15011-15021. doi:10.1021/ja106272zShiju, N. R., Alberts, A. H., Khalid, S., Brown, D. R., & Rothenberg, G. (2011). Mesoporous Silica with Site-Isolated Amine and Phosphotungstic Acid Groups: A Solid Catalyst with Tunable Antagonistic Functions for One-Pot Tandem Reactions. Angewandte Chemie International Edition, 50(41), 9615-9619. doi:10.1002/anie.201101449Shylesh, S., Wagener, A., Seifert, A., Ernst, S., & Thiel, W. R. (2009). Mesoporous Organosilicas with Acidic Frameworks and Basic Sites in the Pores: An Approach to Cooperative Catalytic Reactions. Angewandte Chemie International Edition, 49(1), 184-187. doi:10.1002/anie.200903985Opanasenko, M., Parker, W. O., Shamzhy, M., Montanari, E., Bellettato, M., Mazur, M., ⊠Äejka, J. (2014). Hierarchical Hybrid OrganicâInorganic Materials with Tunable Textural Properties Obtained Using Zeolitic-Layered Precursor. Journal of the American Chemical Society, 136(6), 2511-2519. doi:10.1021/ja410844fCorma, A., Fornes, V., Pergher, S. B., Maesen, T. L. M., & Buglass, J. G. (1998). Delaminated zeolite precursors as selective acidic catalysts. Nature, 396(6709), 353-356. doi:10.1038/24592Corma, A., Diaz, U., Domine, M. E., & FornĂ©s, V. (2000). New Aluminosilicate and Titanosilicate Delaminated Materials Active for Acid Catalysis, and Oxidation Reactions Using H2O2. Journal of the American Chemical Society, 122(12), 2804-2809. doi:10.1021/ja9938130GonzĂĄlez-Arellano, C., Corma, A., Iglesias, M., & SĂĄnchez, F. (2004). Pd(II)-Schiff Base Complexes Heterogenised on MCM-41 and Delaminated Zeolites as Efficient and Recyclable Catalysts for the Heck Reaction. Advanced Synthesis & Catalysis, 346(13-15), 1758-1764. doi:10.1002/adsc.200404119Corma, A., GutiĂ©rrez-Puebla, E., Iglesias, M., Monge, A., PĂ©rez-Ferreras, S., & SĂĄnchez, F. (2006). New Heterogenized Gold(I)-Heterocyclic Carbene Complexes as Reusable Catalysts in Hydrogenation and Cross-Coupling Reactions. Advanced Synthesis & Catalysis, 348(14), 1899-1907. doi:10.1002/adsc.200606163Barth, J.-O., Kornatowski, J., & Lercher*, J. A. (2002). Synthesis of new MCM-36 derivatives pillared with alumina or magnesiaâalumina. Journal of Materials Chemistry, 12(2), 369-373. doi:10.1039/b104824bAlauzun, J., Mehdi, A., Mouawia, R., ReyĂ©, C., & Corriu, R. J. P. (2008). Synthesis of new lamellar materials by self-assembly and coordination chemistry in the solids. Journal of Sol-Gel Science and Technology, 46(3), 383-392. doi:10.1007/s10971-008-1710-7Moreau, J. J. E., Vellutini, L., Wong Chi Man, M., & Bied, C. (2001). New Hybrid OrganicâInorganic Solids with Helical Morphology via H-Bond Mediated SolâGel Hydrolysis of Silyl Derivatives of Chiral (R,R)- or (S,S)-Diureidocyclohexane. Journal of the American Chemical Society, 123(7), 1509-1510. doi:10.1021/ja003843zMoreau, J. J. E., Pichon, B. P., Wong Chi Man, M., Bied, C., Pritzkow, H., Bantignies, J.-L., ⊠Sauvajol, J.-L. (2004). A Better Understanding of the Self-Structuration of Bridged Silsesquioxanes. Angewandte Chemie International Edition, 43(2), 203-206. doi:10.1002/anie.200352485Bellussi, G., Millini, R., Montanari, E., Carati, A., Rizzo, C., Parker, W. O., ⊠Zanardi, S. (2012). A highly crystalline microporous hybrid organicâinorganic aluminosilicate resembling the AFI-type zeolite. Chemical Communications, 48(59), 7356. doi:10.1039/c2cc33417hBellussi, G., Carati, A., Di Paola, E., Millini, R., Parker, W. O., Rizzo, C., & Zanardi, S. (2008). Crystalline hybrid organicâinorganic alumino-silicates. Microporous and Mesoporous Materials, 113(1-3), 252-260. doi:10.1016/j.micromeso.2007.11.024Zanardi, S., Bellussi, G., Carati, A., Di Paola, E., Millini, R., Parker, W. O., & Rizzo, C. (2008). On the crystal structure solution and characterization of ECS-2, a novel microporous hybrid organic-inorganic material. Studies in Surface Science and Catalysis, 965-968. doi:10.1016/s0167-2991(08)80050-xBellussi, G., Montanari, E., Di Paola, E., Millini, R., Carati, A., Rizzo, C., ⊠Zanardi, S. (2011). ECS-3: A Crystalline Hybrid Organic-Inorganic Aluminosilicate with Open Porosity. Angewandte Chemie International Edition, 51(3), 666-669. doi:10.1002/anie.201105496Zanardi, S., Parker, W. O., Carati, A., Botti, G., & Montanari, E. (2013). On the thermal behaviour of the crystalline hybrid organicâinorganic aluminosilicate ECS-3. Microporous and Mesoporous Materials, 172, 200-205. doi:10.1016/j.micromeso.2013.01.029Bellettato, M., Bonoldi, L., Cruciani, G., Flego, C., Guidetti, S., Millini, R., ⊠Zanardi, S. (2014). Flexible Structure of a Thermally Stable Hybrid Aluminosilicate Built with Only the Three-Ring Unit. The Journal of Physical Chemistry C, 118(14), 7458-7467. doi:10.1021/jp5005133S. J. Gregg and K. S. W.Sing, Adsorption, Surface Area and Porosity, Academic Press, London, 1982, pp. 111â190Sing, K. S. W. (1985). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure and Applied Chemistry, 57(4), 603-619. doi:10.1351/pac198557040603Barrett, E. P., Joyner, L. G., & Halenda, P. P. (1951). The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. Journal of the American Chemical Society, 73(1), 373-380. doi:10.1021/ja01145a126Dailey, J. S., & Pinnavaia, T. J. (1992). Silica-pillared derivatives of H+-magadiite, a crystalline hydrated silica. Chemistry of Materials, 4(4), 855-863. doi:10.1021/cm00022a022Roth, W. J., & Dorset, D. L. (2011). Expanded view of zeolite structures and their variability based on layered nature of 3-D frameworks. Microporous and Mesoporous Materials, 142(1), 32-36. doi:10.1016/j.micromeso.2010.11.007Brenn, U., Ernst, H., Freude, D., Herrmann, R., JĂ€hnig, R., Karge, H. ., ⊠Schwieger, W. (2000). Synthesis and characterization of the layered sodium silicate ilerite. Microporous and Mesoporous Materials, 40(1-3), 43-52. doi:10.1016/s1387-1811(00)00241-9Fletcher, R. A. (1987). Synthesis of Kenyaite and Magadiite in the Presence of Various Anions. Clays and Clay Minerals, 35(4), 318-320. doi:10.1346/ccmn.1987.0350410Mochizuki, D., Shimojima, A., Imagawa, T., & Kuroda, K. (2005). Molecular Manipulation of Two- and Three-Dimensional Silica Nanostructures by Alkoxysilylation of a Layered Silicate Octosilicate and Subsequent Hydrolysis of Alkoxy Groups. Journal of the American Chemical Society, 127(19), 7183-7191. doi:10.1021/ja042194eBlake, A. J., Franklin, K. R., & Lowe, B. M. (1988). Preparation and properties of piperazine silicate (EU-19) and a silica polymorph (EU-20). Journal of the Chemical Society, Dalton Transactions, (10), 2513. doi:10.1039/dt9880002513Schreyeck, L., Caullet, P., Mougenel, J.-C., Guth, J.-L., & Marler, B. (1995). A layered microporous aluminosilicate precursor of FER-type zeolite. Journal of the Chemical Society, Chemical Communications, (21), 2187. doi:10.1039/c39950002187Yoshina-Ishii, C., Asefa, T., Coombs, N., MacLachlan, M. J., & Ozin, G. A. (1999). Periodic mesoporous organosilicas, PMOs: fusion of organic and inorganic chemistry âinsideâ the channel walls of hexagonal mesoporous silica. Chemical Communications, (24), 2539-2540. doi:10.1039/a908252bZhou, D., Luo, X.-B., Zhang, H.-L., Dong, C., Xia, Q.-H., Liu, Z.-M., & Deng, F. (2009). Synthesis and characterization of organic-functionalized molecular sieves Ph-SAPO-5 and Ph-SAPO-11. Microporous and Mesoporous Materials, 121(1-3), 194-199. doi:10.1016/j.micromeso.2009.01.033Poli, E., Merino, E., DĂaz, U., Brunel, D., & Corma, A. (2011). SiâC attachment points during solâgel synthesis of organosilicas from 2,8-bis-silylated Trögerâs base as building block precursor. Journal of Materials Chemistry, 21(24), 8524. doi:10.1039/c1jm10426hVan Bokhoven, J. A., Roest, A. L., Koningsberger, D. C., Miller, J. T., Nachtegaal, G. H., & Kentgens, A. P. M. (2000). Changes in Structural and Electronic Properties of the Zeolite Framework Induced by Extraframework Al and La in H-USY and La(x)NaY: A29Si and27Al MAS NMR and27Al MQ MAS NMR Study. The Journal of Physical Chemistry B, 104(29), 6743-6754. doi:10.1021/jp000147cL. J. Bellamy , Advances in infrared group frequencies, Chapman and Hall, London, 1968Rodriguez, I., Iborra, S., Rey, F., & Corma, A. (2000). Heterogeneized Brönsted base catalysts for fine chemicals production: grafted quaternary organic ammonium hydroxides as catalyst for the production of chromenes and coumarins. Applied Catalysis A: General, 194-195, 241-252. doi:10.1016/s0926-860x(99)00371-3CLIMENT, M. (2004). Increasing the basicity and catalytic activity of hydrotalcites by different synthesis procedures. Journal of Catalysis, 225(2), 316-326. doi:10.1016/j.jcat.2004.04.027Prout, F. S., Beaucaire, V. D., Dyrkacz, G. R., Koppes, W. M., Kuznicki, R. E., Marlewski, T. A., ⊠Puda, J. M. (1973). Konevenagel Reaction. Kinetic study of the reaction of (+)-3-methyl-cyclohexanone with malononitrile. The Journal of Organic Chemistry, 38(8), 1512-1517. doi:10.1021/jo00948a015Guyot, J., & Kergomard, A. (1983). CinĂ©tique et mĂ©canisme de la rĂ©action de knoevenagel dans le benzĂšne-2. Tetrahedron, 39(7), 1167-1179. doi:10.1016/s0040-4020(01)91880-0Xu, L., Li, C., Zhang, K., & Wu, P. (2014). Bifunctional Tandem Catalysis on Multilamellar OrganicâInorganic Hybrid Zeolites. ACS Catalysis, 4(9), 2959-2968. doi:10.1021/cs500653pPINE, L. (1984). Prediction of cracking catalyst behavior by a zeolite unit cell size model. Journal of Catalysis, 85(2), 466-476. doi:10.1016/0021-9517(84)90235-
Mechanisms and Kinetics for Sorption of CO2 on Bicontinuous Mesoporous Silica Modified with n-Propylamine
We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.authorCount :7</p
Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts
In this study, we demonstrate how materials science can be combined with the established methods of organic chemistry to find mechanistic bottlenecks and redesign heterogeneous catalysts for improved performance. By using solid-state NMR, infrared spectroscopy, surface and kinetic analysis, we prove the existence of a substrate inhibition in the aldol condensation catalyzed by heterogeneous amines. We show that modifying the structure of the supported amines according to the proposed mechanism dramatically enhances the activity of the heterogeneous catalyst. We also provide evidence that the reaction benefits significantly from the surface chemistry of the silica support, which plays the role of a co-catalyst, giving activities up to two orders of magnitude larger than those of homogeneous amines. This study confirms that the optimization of a heterogeneous catalyst depends as much on obtaining organic mechanistic information as it does on controlling the structure of the support
- âŠ