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The Remarkable Amphoteric Nature of Defective UiO‐66 in Catalytic Reactions

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      Abstract

      One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO‐66(Zr) metal organic framework is shown for acid‐base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment. To elucidate the amphoteric nature of defective UiO‐66, the Oppenauer oxidation of primary alcohols has been theoretically investigated using density functional theory (DFT) and the periodic approach. The presence of acid and basic centers within molecular distances is shown to be crucial for determining the catalytic activity of the material. Hydrated and dehydrated bricks have a distinct influence on the acidity and basicity of the active sites. In any case both functions need to cooperate in a concerted way to enable the chemical transformation. Experimental results on UiO‐66 materials of different defectivity support the theoretical observations made in this work.

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      Most cited references 41

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      Generalized Gradient Approximation Made Simple.

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        A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu.

        The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.
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          A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability.

          Porous crystals are strategic materials with industrial applications within petrochemistry, catalysis, gas storage, and selective separation. Their unique properties are based on the molecular-scale porous character. However, a principal limitation of zeolites and similar oxide-based materials is the relatively small size of the pores, typically in the range of medium-sized molecules, limiting their use in pharmaceutical and fine chemical applications. Metal organic frameworks (MOFs) provided a breakthrough in this respect. New MOFs appear at a high and an increasing pace, but the appearances of new, stable inorganic building bricks are rare. Here we present a new zirconium-based inorganic building brick that allows the synthesis of very high surface area MOFs with unprecedented stability. The high stability is based on the combination of strong Zr-O bonds and the ability of the inner Zr6-cluster to rearrange reversibly upon removal or addition of mu3-OH groups, without any changes in the connecting carboxylates. The weak thermal, chemical, and mechanical stability of most MOFs is probably the most important property that limits their use in large scale industrial applications. The Zr-MOFs presented in this work have the toughness needed for industrial applications; decomposition temperature above 500 degrees C and resistance to most chemicals, and they remain crystalline even after exposure to 10 tons/cm2 of external pressure.
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            Author and article information

            Affiliations
            [ 1 ] Center for Molecular ModelingGhent University Technologiepark 903, B- 9052 ZwijnaardeBelgium
            [ 2 ] Centre for Surface Chemistry and CatalysisUniversity of Leuven, Leuven Chem&Tech Celestijnenlaan 200F P.O. Box 2461, B- 3001 LeuvenBelgium
            Contributors
            ORCID: http://orcid.org/0000-0003-2206-178X, veronique.vanspeybroeck@ugent.be
            Journal
            ChemCatChem
            ChemCatChem
            10.1002/(ISSN)1867-3899
            CCTC
            Chemcatchem
            John Wiley and Sons Inc. (Hoboken )
            1867-3880
            1867-3899
            04 May 2017
            22 June 2017
            : 9
            : 12 , French Conference on Catalysis ( doiID: 10.1002/cctc.v9.12 )
            : 2203-2210
            5499726
            10.1002/cctc.201601689
            CCTC201601689
            © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

            This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

            Counts
            Figures: 14, Tables: 2, References: 48, Pages: 8, Words: 0
            Product
            Funding
            Funded by: European Research Council
            Award ID: 647755-DYNPOR
            Award ID: 641887
            Funded by: Federaal Wetenschapsbeleid
            Award ID: IAP/7/05
            Funded by: Fonds Wetenschappelijk Onderzoek
            Award ID: 3G048612
            Categories
            Full Paper
            Full Papers
            Custom metadata
            2.0
            cctc201601689
            June 22, 2017
            Converter:WILEY_ML3GV2_TO_NLMPMC version:5.1.2 mode:remove_FC converted:06.07.2017

            Catalysis

            brønsted base site, catalysis, lewis acid site, dft, kinetics

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