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1.
Artigo em Inglês | MEDLINE | ID: mdl-32453899

RESUMO

There are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet-like crystal morphology, large surface area, fully four-coordinated Al species, and abundant acidic sites. Methanol-to-propylene (MTP) tests reveal that the Al-ITH zeolite shows much higher selectivity for propylene and longer lifetime than commercial ZSM-5. FCC tests show that Al-ITH zeolite is a good candidate as a shape-selective FCC additive for enhancing propylene and butylene selectivity.

2.
J Am Chem Soc ; 141(45): 18318-18324, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31644275

RESUMO

A large amount of zeolite structures are still not synthetically available or not available in the form of aluminosilicate currently. Despite significant progress in the development of predictive concepts for zeolite synthesis, accessing some of these new materials is still challenging. One example is the IWR structure as well. Despite successful synthesis of Ge-based IWR zeolites, direct synthesis of aluminosilicate IWR zeolite is still not successful. In this report we show how a suitable organic structure directing agent (OSDA), through modeling of an OSDA/zeolite cage interaction, could access directly the aluminum-containing IWR structure (denoted as COE-6), which might allow access to new classes of materials and thus open opportunities in valuable chemical applications. The experimental results reveal that the COE-6 zeolites with a SiO2/Al2O3 ratio as low as 30 could be obtained. Very interestingly, the COE-6 zeolite has much higher hydrothermal and thermal stabilities than those of the conventional Ge-Al-IWR zeolite. In methanol-to-propylene (MTP) reaction, the COE-6 zeolite exhibits excellent selectivity for propylene, offering a potential catalyst for MTP reaction in the future.

3.
Acta Crystallogr A Found Adv ; 74(Pt 2): 93-101, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29493538

RESUMO

Nanoscaled porous materials such as zeolites have attracted substantial attention in industry due to their catalytic activity, and their performance in sorption and separation processes. In order to understand the properties of such materials, current research focuses increasingly on the determination of structural features beyond the averaged crystal structure. Small particle sizes, various types of disorder and intergrown structures render the description of structures at atomic level by standard crystallographic methods difficult. This paper reports the characterization of a strongly disordered zeolite structure, using a combination of electron exit-wave reconstruction, automated diffraction tomography (ADT), crystal disorder modelling and electron diffraction simulations. Zeolite beta was chosen for a proof-of-principle study of the techniques, because it consists of two different intergrown polymorphs that are built from identical layer types but with different stacking sequences. Imaging of the projected inner Coulomb potential of zeolite beta crystals shows the intergrowth of the polymorphs BEA and BEB. The structures of BEA as well as BEB could be extracted from one single ADT data set using direct methods. A ratio for BEA/BEB = 48:52 was determined by comparison of the reconstructed reciprocal space based on ADT data with simulated electron diffraction data for virtual nanocrystals, built with different ratios of BEA/BEB. In this way, it is demonstrated that this smart interplay of the above-mentioned techniques allows the elaboration of the real structures of functional materials in detail - even if they possess a severely disordered structure.

4.
Angew Chem Int Ed Engl ; 57(15): 4093-4097, 2018 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-29377499

RESUMO

In order to design more powerful electrocatalysts, developing our understanding of the role of the surface structure and composition of widely abundant bulk materials is crucial. This is particularly true in the search for alternative hydrogen evolution reaction (HER) catalysts to replace platinum. We report scanning electrochemical cell microscopy (SECCM) measurements of the (111)-crystal planes of Fe4.5 Ni4.5 S8 , a highly active HER catalyst. In combination with structural characterization methods, we show that this technique can reveal differences in activity arising from even the slightest compositional changes. By probing electrochemical properties at the nanoscale, in conjunction with complementary structural information, novel design principles are revealed for application to rational material synthesis.

5.
Dalton Trans ; 45(25): 10155-64, 2016 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-27151550

RESUMO

ITQ-8 is a new hydrous layer silicate (HLS) with a chemical composition of [C4H8(C7H13N)2]8 [Si64O128(OH)16]·48H2O per unit cell. The synthesis of ITQ-8 was first described in 2002 by Díaz-Cabañas et al., the structure of this material, however, remained unsolved at that time. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and FTIR spectroscopy confirmed that ITQ-8 is a layer silicate. The XRD powder pattern was indexed in the monoclinic system with lattice parameters of a0 = 35.5168(5) Å, b0 = 13.3989(2) Å, c0 = 16.0351(2) Å, ß = 106.74(2)°. The crystal structure was solved by simulated annealing. Rietveld refinement of the structure in space group C2/c converged to residual values of RBragg = 0.023, RF = 0.022 and chi(2) = 2.3 confirming the structure model. The structure of ITQ-8 contains silicate layers with a topology that resembles a (11-1) section of the framework of zeolite levyne. So far, this layer topology is unique among layer silicates. The layer can be regarded as made up of 4-, 6-, double-six and 8-rings which are interconnected to form cup-like "half-cages". Unlike other HLSs, which possess impermeable silicate layers, ITQ-8 contains 8-rings pores with a free diameter of 3.5 Å × 3.4 Å and can be regarded as a "small-pore layer silicate". In the crystal structure, the organic cations, 1,4-diquiniclidiniumbutane, used as structure directing agents during synthesis are intercalated between the silicate layers. Clusters (bands) of water molecules which are hydrogen bonded to each other and to the terminal Si-OH/Si-O(-) groups are located between the organic cations and interconnect the silicate layers. ITQ-8 is a very interesting material as precursor for the synthesis of microporous framework silicates by topotactic condensation or interlayer expansion reactions leading to 3D micro-pore systems which may be useful in applications as e.g. catalysts, catalyst supports and adsorbents of for separation.

6.
Angew Chem Int Ed Engl ; 53(27): 7058-62, 2014 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-24838592

RESUMO

A mixed-linker solid-solution approach was employed to modify the metal sites and introduce structural defects into the mixed-valence Ru(II/III) structural analogue of the well-known MOF family [M3(II,II)(btc)2] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene-1,3,5-tricarboxylate), with partly missing carboxylate ligators at the Ru2 paddle-wheels. Incorporation of pyridine-3,5-dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed-linker isoreticular derivatives of Ru-MOF, which display characteristics unlike those of the defect-free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the "defective" variants in the dissociative chemisorption of CO2, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins.


Assuntos
Compostos Orgânicos/química , Rutênio/química , Dióxido de Carbono/química , Monóxido de Carbono/química , Catálise , Complexos de Coordenação/química , Hidrogenação , Oxirredução
7.
Astrobiology ; 12(11): 1042-54, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23095098

RESUMO

The enthalpies of formation of synthetic MgSO(4)·4H(2)O (starkeyite) and MgSO(4)·3H(2)O were obtained by solution calorimetry at T=298.15 K. The resulting enthalpies of formation from the elements are [Formula: see text] (starkeyite)=-2498.7±1.1 kJ·mol(-1) and [Formula: see text] (MgSO(4)·3H(2)O)=-2210.3±1.3 kJ·mol(-1). The standard entropy of starkeyite was derived from low-temperature heat capacity measurements acquired with a physical property measurement system (PPMS) in the temperature range 5 K

Assuntos
Sulfato de Magnésio/química , Varredura Diferencial de Calorimetria , Entropia , Cinética , Reprodutibilidade dos Testes , Temperatura , Termodinâmica
8.
Dalton Trans ; 41(40): 12408-15, 2012 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-22940750

RESUMO

For the first time, the co-templating ionothermal methodology was used in the preparation of layered aluminophosphate materials. With the addition of either 1,2-ethylenediamine or 1,6-hexanediamine to the ionic liquid 1-ethyl-3-methyl imidazolium chloride, two new 2D layered aluminophosphates RUB-A1 [Al(3)P(4)O(16)][NH(3)CH(2)CH(2)NH(3)](0.5)[C(6)N(2)H(11)](2) and RUB-A2 [Al(3)P(4)O(16)][NH(3)(CH(2))(6)NH(3)][NH(3)(CH(2))(6)NH(2)](0.5)[C(6)N(2)H(11)](0.5)[H(2)O] have been synthesized ionothermally by co-templating. The structure of RUB-A1 has been determined from single-crystal X-ray diffraction data using direct methods, while the structure of RUB-A2 has been solved ab initio from powder X-ray diffraction data with limited resolution using direct-space methods. Both of these two compounds have a 2D layered structure consisting of macroanionic sheets of composition [Al(3)P(4)O(16)](3-) stacked in an AAAA sequence. The inorganic layers are built up from alternatively vertex-sharing [AlO(4)]- and [PO(3)(=O)]-tetrahedral units forming a 4.6.8 and a 4.6.12 network for RUB-A1 and RUB-A2, respectively. The layer topology of RUB-A1 is closely related to the previously known 4.6.8-layer topology but with a different sequence of phosphoryl group orientation. Combining the results of structure analysis with the NMR, chemical analysis and TG-DTA experiments, we show that both the ionic liquid cation and the protonated diamines are located in the interlayer space and together direct the formation of these two structures.

9.
Inorg Chem ; 36(21): 4697-4701, 1997 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-11670146

RESUMO

A new thiostannate, (C(12)H(25)NH(3))(4)[Sn(2)S(6)].2H(2)O, was synthesized from SnCl(4), Na(2)S, and dodecylamine (DDA) in the ethanol-water two-solvent system at room temperature. First a suspension was obtained. With increasing crystallization time, single crystals up to several millimeters in size were found at the bottom of the vessel. The compound was characterized by single-crystal X-ray diffraction, solid state (119)Sn CPMAS NMR and (13)C CPMAS NMR, IR absorption spectroscopy, and thermal analysis. The crystal data are a = 7.533(2) Å, b = 10.162(2) Å, c = 21.688(4) Å, alpha = 101.22(3) degrees, beta = 90.76(3) degrees, gamma = 101.82(3) degrees, triclinic, space group = P&onemacr;, and Z = 1. The structure consists of one [Sn(2)S(6)](4)(-) anion, four n-dodecylammonium cations, and two water molecules per unit cell. The [Sn(2)S(6)](4)(-) dimers are formed by two edge-sharing [SnS(4)] tetrahedra. The hydrocarbon chains of the cations are straight with the chain direction running parallel to [001]. The chains are in van der Waals contact to each other with the nitrogen atoms pointing in opposite directions for neighboring chains. The positions of all hydrogen atoms were determined; in particular three positions were found which may suggest that the nitrogen atoms are protonated to form cationic groups. The nonorganic constituents of the structure, i.e., anions, water molecules, and ammonium groups, interact to form an infinite layer-like unit parallel to (001).

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