Modulating active sites in MOFs for improved Lewis acid or base catalysis

International audienc

Influence of functionalization of terephthalate linker on the catalytic activity of UiO-66 for epoxide ring opening

[EN] A series of five isostructural zirconium terephthalate UiO-66 metal organic frameworks bearing different functional groups on the terephthalate linker (UiO-66-X; X = H, NH2, NO2, Br, Cl,) have been successfully prepared and characterized. UiO-66-X materials were evaluated as heterogeneous catalysts for the epoxide ring opening of styrene oxide by methanol, observing an increase in the initial reaction rate from UiO-66-H to UiO-66-Br, over one order of magnitude. The reactivity order, however, does not follow a linear relationship between the Hammett constant value of the substituent and the initial reaction rate. UiO-66-Br exhibits a wide scope, its activity depending on the structure of epoxide and nucleophile. The absence of Zr leaching to the solution together with the preservation of the UiO-66-X crystallinity confirms the stability of the framework under the reaction conditions. Nevertheless, UiO-66 undergoes a progressive deactivation upon reuse that was attributed to a strong adsorption of the reaction product.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2015-69153 and CTQ2014-53292-R and Generalitat Valenciana (Prometeo 2013/14) and is grateful acknowledged. We also thank EU under the Being Energy contract for partial funding. J.F.B. thanks the Universitat Politecnica de Valencia for a postgraduate scholarship. S.N. thanks the Spanish Ministerio de Educacion, Cultura y Deporte for Jose Castillejo mobility programme (CAS14/00067).Blandez, JF.; Santiago-Portillo, A.; Navalón Oltra, S.; Gimenez Marques, M.; Alvaro Rodríguez, MM.; Horcajada, P.; García Gómez, H. (2016). Influence of functionalization of terephthalate linker on the catalytic activity of UiO-66 for epoxide ring opening. Journal of Molecular Catalysis A Chemical. 425:332-339. https://doi.org/10.1016/j.molcata.2016.10.022S33233942

MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst

A bifunctional MOF catalyst containing coordinatively unsaturated Cr3+ sites and palladium nanoparticles (Pd@MIL-101) has been used for the cyclization of citronellal to isopulegol and for the one-pot tandem isomerization/hydrogenation of citronellal to menthol. The MOF was found to be stable under the reaction conditions used, and the results obtained indicate that the performance of this bifunctional solid catalyst is comparable with other state-of-the-art materials for the tandem reaction: Full citronellal conversion was attained over Pd@MIL-101 in 18 h, with 86% selectivity to menthols and a diastereoselectivity of 81% to the desired (-)-menthol, while up to 30 h were necessary for attaining similar values over Ir/H-beta under analogous reaction conditions.Financial support by Ministerio de Educacion y Ciencia e Innovacion (Project MIYCIN, CSD2009-00050; PROGRAMA CONSOLIDER. INGENIO 2009), Generalidad Valenciana (GV PROMETEO/2008/130) and the CSIC (Proyectos Intramurales Especiales 201080I020) is gratefully acknowledged.García Cirujano, F.; Llabrés I Xamena, FX.; Corma Canós, A. (2012). MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst. Dalton Transactions. 41:4249-4254. https://doi.org/10.1039/c2dt12480gS4249425441Corma, A., García, H., & Llabrés i Xamena, F. X. (2010). Engineering Metal Organic Frameworks for Heterogeneous Catalysis. Chemical Reviews, 110(8), 4606-4655. doi:10.1021/cr9003924Farrusseng, D., Aguado, S., & Pinel, C. (2009). Metal-Organic Frameworks: Opportunities for Catalysis. Angewandte Chemie International Edition, 48(41), 7502-7513. doi:10.1002/anie.200806063Lee, J., Farha, O. K., Roberts, J., Scheidt, K. A., Nguyen, S. T., & Hupp, J. T. (2009). Metal–organic framework materials as catalysts. 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Chemical Communications, (35), 4192. doi:10.1039/b718371bVermoortele, F., Ameloot, R., Vimont, A., Serre, C., & De Vos, D. (2011). An amino-modified Zr-terephthalate metal–organic framework as an acid–base catalyst for cross-aldol condensation. Chem. Commun., 47(5), 1521-1523. doi:10.1039/c0cc03038dWu, P., Wang, J., Li, Y., He, C., Xie, Z., & Duan, C. (2011). Luminescent Sensing and Catalytic Performances of a Multifunctional Lanthanide-Organic Framework Comprising a Triphenylamine Moiety. Advanced Functional Materials, 21(14), 2788-2794. doi:10.1002/adfm.201100115Pan, Y., Yuan, B., Li, Y., & He, D. (2010). Multifunctional catalysis by Pd@MIL-101: one-step synthesis of methyl isobutyl ketone over palladium nanoparticles deposited on a metal–organic framework. Chemical Communications, 46(13), 2280. doi:10.1039/b922061eCliment, M. J., Corma, A., Guil-López, R., Iborra, S., & Primo, J. (1998). Use of Mesoporous MCM-41 Aluminosilicates as Catalysts in the Preparation of Fine Chemicals. Journal of Catalysis, 175(1), 70-79. doi:10.1006/jcat.1998.1970Climent, M. J., Corma, A., Iborra, S., & Velty, A. (2002). Designing the adequate base solid catalyst with Lewis or Bronsted basic sites or with acid–base pairs. Journal of Molecular Catalysis A: Chemical, 182-183, 327-342. doi:10.1016/s1381-1169(01)00501-5Boronat, M., Climent, M. J., Corma, A., Iborra, S., Montón, R., & Sabater, M. J. (2010). Bifunctional Acid-Base Ionic Liquid Organocatalysts with a Controlled Distance Between Acid and Base Sites. Chemistry - A European Journal, 16(4), 1221-1231. doi:10.1002/chem.200901519Corma, A., Díaz, U., García, T., Sastre, G., & Velty, A. (2010). Multifunctional Hybrid Organic−Inorganic 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/ja106272zFerey, G. (2005). A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area. Science, 309(5743), 2040-2042. doi:10.1126/science.1116275Corma, A., & Renz, M. (2004). Sn-Beta zeolite as diastereoselective water-resistant heterogeneous Lewis-acid catalyst for carbon–carbon bond formation in the intramolecular carbonyl–ene reaction. Chem. Commun., (5), 550-551. doi:10.1039/b313738dIosif, F., Coman, S., Pârvulescu, V., Grange, P., Delsarte, S., Vos, D. D., & Jacobs, P. (2004). Ir-Beta zeolite as a heterogeneous catalyst for the one-pot transformation of citronellal to menthol. Chem. Commun., (11), 1292-1293. doi:10.1039/b403692aNeaţu, F., Coman, S., Pârvulescu, V. I., Poncelet, G., De Vos, D., & Jacobs, P. (2009). Heterogeneous Catalytic Transformation of Citronellal to Menthol in a Single Step on Ir-Beta Zeolite Catalysts. Topics in Catalysis, 52(9), 1292-1300. doi:10.1007/s11244-009-9270-9MERTENS, P., VERPOORT, F., PARVULESCU, A., & DEVOS, D. (2006). Pt/H-beta zeolites as productive bifunctional catalysts for the one-step citronellal-to-menthol conversion. Journal of Catalysis, 243(1), 7-13. doi:10.1016/j.jcat.2006.06.017Da Silva Rocha, K. A., Robles-Dutenhefner, P. A., Sousa, E. M. B., Kozhevnikova, E. F., Kozhevnikov, I. V., & Gusevskaya, E. V. (2007). Pd–heteropoly acid as a bifunctional heterogeneous catalyst for one-pot conversion of citronellal to menthol. Applied Catalysis A: General, 317(2), 171-174. doi:10.1016/j.apcata.2006.10.019Trasarti, A. F., Marchi, A. J., & Apesteguı́a, C. R. (2004). Highly selective synthesis of menthols from citral in a one-step process. Journal of Catalysis, 224(2), 484-488. doi:10.1016/j.jcat.2004.03.016TRASARTI, A., MARCHI, A., & APESTEGUIA, C. (2007). Design of catalyst systems for the one-pot synthesis of menthols from citral. Journal of Catalysis, 247(2), 155-165. doi:10.1016/j.jcat.2007.01.016Alaerts, L., Séguin, E., Poelman, H., Thibault-Starzyk, F., Jacobs, P. A., & De Vos, D. E. (2006). Probing the Lewis Acidity and Catalytic Activity of the Metal–Organic Framework [Cu3(btc)2] (BTC=Benzene-1,3,5-tricarboxylate). Chemistry - A European Journal, 12(28), 7353-7363. doi:10.1002/chem.200600220Horcajada, P., Surblé, S., Serre, C., Hong, D.-Y., Seo, Y.-K., Chang, J.-S., … Férey, G. (2007). Synthesis and catalytic properties of MIL-100(Fe), an iron(iii) carboxylate with large pores. Chem. Commun., (27), 2820-2822. doi:10.1039/b704325bRavon, U., Chaplais, G., Chizallet, C., Seyyedi, B., Bonino, F., Bordiga, S., … Farrusseng, D. (2010). Investigation of Acid Centers in MIL-53(Al, Ga) for Brønsted-Type Catalysis: In Situ FTIR and Ab Initio Molecular Modeling. ChemCatChem, 2(10), 1235-1238. doi:10.1002/cctc.201000055Vimont, A., Leclerc, H., Maugé, F., Daturi, M., Lavalley, J.-C., Surblé, S., … Férey, G. (2007). Creation of Controlled Brønsted Acidity on a Zeotypic Mesoporous Chromium(III) Carboxylate by Grafting Water and Alcohol Molecules. The Journal of Physical Chemistry C, 111(1), 383-388. doi:10.1021/jp064686

Host-guest and guest-guest interactions between xylene isomers confined in the MIL-47(V) pore system

The porous MIL-47 material shows a selective adsorption behavior for para-, ortho-, and meta-isomers of xylenes, making the material a serious candidate for separation applications. The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion-corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior

Liquid-Phase Adsorption and Separation of Xylene Isomers by the Flexible Porous Metal-Organic Framework MIL-53(Fe)

We report a study of the use of the porous metal–organic framework material MIL-53(Fe), FeIII(OH)0.8F0.2[O2C–C6H4–CO2], for the separation of BTEX mixtures (benzene, toluene, ethylbenzene, and the three xylene isomers). Crystal structures of the three host:guest materials MIL-53(Fe)[xylene], where xylene = the ortho, meta, or para isomer of dimethylbenzene, have been solved and refined from powder X-ray diffraction. Each exhibits a fully expanded form with a variety of host:guest and guest:guest interactions responsible for stabilizing the structure. While the ortho- and meta- isomers present a similar arrangement when occluded in the MIL-53 host, the para-xylene shows a distinctly different set of interactions with the host. Upon thermal treatment, xylenes are partially lost to give crystalline phases MIL-53(Fe)[xylene]0.5, the structures of which have also been solved. The kinetics of uptake of each xylene by MIL-53(Fe)[H2O], in which the water is replaced by the organic guest, have been studied using time-resolved energy-dispersive X-ray diffraction: this shows differences in kinetics of the adsorption of the three isomers. Under chromatographic conditions in heptane at 293 K, anhydrous MIL-53(Fe) is able to separate the three xylene isomers with elution of the para-xylene before the other two isomers, and at 323 K the host is able to resolve all components of the BTEX mixture

Bulk-to-Surface Proton-Coupled Electron Transfer Reactivity of the Metal-Organic Framework MIL-125

Stoichiometric proton-coupled electron transfer (PCET) reactions of the metal-organic framework (MOF) MIL-125, Ti8O8(OH)4(bdc)6 (bdc = terephthalate), are described. In the presence of UV light and 2-propanol, MIL-125 was photoreduced to a maximum of 2( e-/H+) per Ti8 node. This stoichiometry was shown by subsequent titration of the photoreduced material with the 2,4,6-tri- tert-butylphenoxyl radical. This reaction occurred by PCET to give the corresponding phenol and the original, oxidized MOF. The high level of charging, and the independence of charging amount with particle size of the MOF samples, shows that the MOF was photocharged throughout the bulk and not only at the surface. NMR studies showed that the product phenol is too large to fit in the pores, so the phenoxyl reaction must have occurred at the surface. Attempts to oxidize photoreduced MIL-125 with pure electron acceptors resulted in multiple products, underscoring the importance of removing e- and H+ together. Our results require that the e- and H+ stored within the MOF architecture must both be mobile to transfer to the surface for reaction. Analogous studies on the soluble cluster Ti8O8(OOC tBu)16 support the notion that reduction occurs at the Ti8 MOF nodes and furthermore that this reduction occurs via e-/H+ (H-atom) equivalents. The soluble cluster also suggests degradation pathways for the MOFs under extended irradiation. The methods described are a facile characterization technique to study redox-active materials and should be broadly applicable to, for example, porous materials like MOFs.status: publishe