Meltable, Glass-Forming, Iron Zeolitic Imidazolate Frameworks.

We describe the first meltable iron-based zeolitic imidazolate framework (ZIF), denoted MUV-24. This material, elusive from direct synthesis, is obtained from the thermal treatment of [Fe3(im)6(Him)2], which yields Fe(im)2 upon loss of the neutral imidazole molecules. Different crystalline phase transformations are observed upon further heating, until the material melts at 482 °C. Vitrification upon cooling of the liquid phase gives rise to the first Fe-metal-organic framework glass. X-ray total scattering experiments show that the tetrahedral environment of the crystalline solids is maintained in the glass, whereas nanoindentation measurements reveal an increase in Young's modulus, in agreement with stiffening upon vitrification.

Synthesis and Structure of a 22 × 12 × 12 Extra-Large Pore Zeolite ITQ-56 Determined by 3D Electron Diffraction.

A multidimensional extra-large pore germanosilicate, denoted ITQ-56, has been synthesized by using modified memantine as an organic structure-directing agent. ITQ-56 crystallizes as plate-like nanocrystals. Its structure was determined by 3D electron diffraction/MicroED. The structure of ITQ-56 contains extra-large 22-ring channels intersecting with straight 12-ring channels. ITQ-56 is the first zeolite with 22-ring pores, which is a result of ordered vacancies of double 4-ring (d4r) units in a fully connected zeolite framework. The framework density is as low as 12.4 T atoms/1000 Å3. The discovery of the ITQ-56 structure not only fills the missing member of extra-large pore zeolite with 22-ring channels but also creates a new approach of making extra-large pore zeolites by introducing ordered vacancies in zeolite frameworks.

ITQ-69: A Germanium-Containing Zeolite and its Synthesis, Structure Determination, and Adsorption Properties.

In this work, a new zeolite named as ITQ-69, has been synthesized, characterized and its application as selective adsorbent for industrially relevant light olefins/paraffins separations has been assessed. This material has been obtained as pure germania as well as silica-germania zeolites with different Si/Ge ratios using a diquaternary ammonium cation as organic structure directing agent. Its structure was determined by single-crystal X-Ray diffraction showing a triclinic unit cell forming a tridirectional small pore channel system (8×8×8R). Also, it has been found that Si preferentially occupies some special T sites of the structure as deduced from Rietveld analysis of the powder X-ray diffraction patterns. In addition, the new zeolite ITQ-69 has been found to be stable upon calcination and thus, its adsorption properties were evaluated, showing a promising kinetic selectivity for light olefin separations in the C3 fraction.

Use of Alkylarsonium Directing Agents for the Synthesis and Study of Zeolites.

Expanding the previously known family of -onium (ammonium, phosphonium, and sulfonium) organic structure-directing agents (OSDAs) for the synthesis of zeolite MFI, a new member, the arsonium cation, is used for the first time. The new group of tetraalkylarsonium cations has allowed the synthesis of the zeolite ZSM-5 with several different chemical compositions, opening a route for the synthesis of zeolites with a new series of OSDA. Moreover, the use of As replacing N in the OSDA allows the introduction of probe atoms that facilitate the study of these molecules by powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (MAS NMR), and X-ray absorption spectroscopy (XAS). Finally, the influence of trivalent elements such as B, Al, or Ga isomorphically replacing Si atoms in the framework structure and its interaction with the As species has been studied. The suitability of the tetraalkylarsonium cation for carrying out the crystallization of zeolites is demonstrated along with the benefit of the presence of As atoms in the occluded OSDA, which allows its advanced characterization as well as the study of its evolution during OSDA removal by thermal treatments.

An Ultrahigh CO2-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures.

We report the formation of an ultrahigh CO2-loaded pure-SiO2 silicalite-1 structure at high pressure (0.7 GPa) from the interaction of empty zeolite and fluid CO2 medium. The CO2-filled structure was characterized in situ by means of synchrotron powder X-ray diffraction. Rietveld refinements and Fourier recycling allowed the location of 16 guest carbon dioxide molecules per unit cell within the straight and sinusoidal channels of the porous framework to be analyzed. The complete filling of pores by CO2 molecules favors structural stability under compression, avoiding pressure-induced amorphization below 20 GPa, and significantly reduces the compressibility of the system compared to that of the parental empty one. The structure of CO2-loaded silicalite-1 was also monitored at high pressures and temperatures, and its thermal expansivity was estimated.

Ultrafast Electron Diffraction Tomography for Structure Determination of the New Zeolite ITQ-58.

In this work a new ultrafast data collection strategy for electron diffraction tomography is presented that allows reducing data acquisition time by one order of magnitude. This methodology minimizes the radiation damage of beam-sensitive materials, such as microporous materials. This method, combined with the precession of the electron beam, provides high quality data enabling the determination of very complex structures. Most importantly, the implementation of this new electron diffraction methodology is easily affordable in any modern electron microscope. As a proof of concept, we have solved a new highly complex zeolitic structure named ITQ-58, with a very low symmetry (triclinic) and a large unit cell volume (1874.6 Å(3)), containing 16 silicon and 32 oxygen atoms in its asymmetric unit, which would be very difficult to solve with the state of the art techniques.

High-Performance of Gas Hydrates in Confined Nanospace for Reversible CH4 /CO2 Storage.

The molecular exchange of CH4 for CO2 in gas hydrates grown in confined nanospace has been evaluated for the first time using activated carbons as a host structure. The nano-confinement effects taking place inside the carbon cavities and the exceptional physicochemical properties of the carbon structure allows us to accelerate the formation and decomposition process of the gas hydrates from the conventional timescale of hours/days in artificial bulk systems to minutes in confined nanospace. The CH4 /CO2 exchange process is fully reversible with high efficiency at practical temperature and pressure conditions. Furthermore, these activated carbons can be envisaged as promising materials for long-distance natural gas and CO2 transportation because of the combination of a high storage capacity, a high reversibility, and most important, with extremely fast kinetics for gas hydrate formation and release.

A new microporous zeolitic silicoborate (ITQ-52) with interconnected small and medium pores.

A new zeolite (named as ITQ-52) having large cavities and small and medium channels has been synthesized. This was achieved by using a new family of amino-phosphonium cations as organic structure directing agents (OSDA). These cations contain P-C and P-N bonds, and therefore they lie between previously reported P-containing OSDA, such as tetraalkylphosphonium and phosphazenes. In this study, it has been found that 1,4-butanediylbis[tris(dimethylamino)]phosphonium dication is a very efficient OSDA for crystallization of several zeolites, and in some particular conditions, the new zeolite ITQ-52 was synthesized as a pure phase. The structure of ITQ-52 has been solved using high-resolution synchrotron X-ray powder diffraction data of the calcined solid. This new zeolite crystallizes in the space group I2/m, with cell parameters a = 17.511 Å, b = 17.907 Å, c = 12.367 Å, and ß = 90.22°. The topology of ITQ-52 can be described as a replication of a composite building unit with ring notation [4(3)5(4)6(1)] that gives rise to the formation of an interconnected 8R and 10R channel system.

Sugar-based synthesis of an enantiomorphically pure zeolite.

Zeolites, well-known by their high selectivities in catalytic and separation processes due to their porous nature, play a crucial role in various applications. One significant long-term objective is the synthesis of enantiopure zeolites, potentially enabling enantioselective processes. Earlier attempts result in partial success, yielding some enantiomorphically enriched zeolites. In this study, we introduce a zeolite synthesis approach utilizing chiral organic structure directing agents (ch-OSDAs) derived from sugars, guiding the crystallization process toward achieving enantiomorphically pure S-STW zeolite. The purity of the zeolite is confirmed through extensive analyses of individual crystals using single-crystal X-ray diffraction, extracting Flack parameters and space groups. Theoretical and structural investigations confirm that the sugar-derived ch-OSDA perfectly fits the characteristic helicoidal channel of the zeolite structure, featuring its efficacy in achieving enantiopure zeolites.

Synthesis of a novel zeolite through a pressure-induced reconstructive phase transition process.

The first pressure-induced solid-phase synthesis of a zeolite has been found through compression of a common zeolite, ITQ-29 (see scheme, Si yellow, O red). The new microporous structure, ITQ-50, has a unique structure and improved performance for propene/propane separation with respect the parent material ITQ-29.

Synthesis and structure determination of a new microporous zeolite with large cavities connected by small pores.

A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure-directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group Immm with cell parameters a = 19.6007(8) Å, b = 18.3274(7) Å, and c = 16.5335(6) Å. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered-ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units.

Synthesis design and structure of a multipore zeolite with interconnected 12- and 10-MR channels.

A new molecular sieve, ITQ-38, containing interconnected large and medium pores in its structure has been synthesized. The rational combination of dicationic piperidine-derivative molecules as organic structure directing agents (OSDAs) with germanium and boron atoms in alkaline media has allowed the synthesis of ITQ-38 zeolite. High-resolution transmission electron microscopy (HRTEM) has been used to elucidate the framework topology of ITQ-38, revealing the presence of domains of perfect ITQ-38 crystals as well as very small areas containing nanosized ITQ-38/ITQ-22 intergrowths. The structure of ITQ-38 is highly related to ITQ-22 and the recently described polymorph C of ITQ-39 zeolite. It shares a common building layer with ITQ-22 and contains the same building unit as the polymorph C of ITQ-39. All three structures present similar framework density, 16.1 T atoms/1000 Å(3).

Insights into the formation of metal carbon nanocomposites for energy storage using hybrid NiFe layered double hydroxides as precursors.

NiFe-carbon magnetic nanocomposites prepared using hybrid sebacate intercalated layered double hydroxides (LDHs) as precursors are shown to be of interest as supercapacitors. Here, the low-temperature formation mechanism of these materials has been deciphered by means of a combined study using complementary in situ (temperature-dependent) techniques. Specifically, studies involving X-ray powder diffraction, thermogravimetry coupled to mass spectrometry (TG-MS), statistical Raman spectroscopy (SRS), aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have been carried out. The experimental results confirm the early formation of FeNi3 nanoparticles at ca. 200-250 °C, preceding the concerted collapse of the starting NiFe-LDH laminar structure over just 50 °C (from 350 to 400 °C). At the same time, the catalytic interactions between the metallic atoms and the organic molecules permit the concomitant formation of a graphitic carbon matrix leading to the formation of the final FeNi3-carbon nanocomposite. Furthermore, in situ temperature-dependent experiments in the presence of the intrinsic magnetic field of the STEM-EELS allow observing the complete metal segregation of Ni and Fe even at 400 °C. These results provide fundamental insights into the catalytic formation of carbon-based nanocomposites using LDHs as precursors and pave the way for the fine-tuning of their properties, with special interest in the field of energy storage and conversion.

Cobalt Metal-Organic Framework Based on Two Dinuclear Secondary Building Units for Electrocatalytic Oxygen Evolution.

The synthesis of a new microporous metal-organic framework (MOF) based on two secondary building units, with dinuclear cobalt centers, has been developed. The employment of a well-defined cobalt cluster results in an unusual topology of the Co2-MOF, where one of the cobalt centers has three open coordination positions, which has no precedent in MOF materials based on cobalt. Adsorption isotherms have revealed that Co2-MOF is in the range of best CO2 adsorbents among the carbon materials, with very high CO2/CH4 selectivity. On the other hand, dispersion of Co2-MOF in an alcoholic solution of Nafion gives rise to a composite (Co2-MOF@Nafion) with great resistance to hydrolysis in aqueous media and good adherence to graphite electrodes. In fact, it exhibits high electrocatalytic activity and robustness for the oxygen evolution reaction (OER), with a turnover frequency number value superior to those reported for similar electrocatalysts. Overall, this work has provided the basis for the rational design of new cobalt OER catalysts and related materials employing well-defined metal clusters as directing agents of the MOF structure.

Synthesis and structure determination via ultra-fast electron diffraction of the new microporous zeolitic germanosilicate ITQ-62.

Here, we present the synthesis and structure determination of the new zeolite ITQ-62. Its structure was determined via ultra-fast electron diffraction tomography and refined using powder XRD data of the calcined material. This new zeolite contains a tridirectional channel system of highly distorted 8-rings, as well as a monodirectional 12-ring channel system.

Gas confinement in compartmentalized coordination polymers for highly selective sorption.

Discrimination between different gases is an essential aspect for industrial and environmental applications involving sensing and separation. Several classes of porous materials have been used in this context, including zeolites and more recently MOFs. However, to reach high selectivities for the separation of gas mixtures is a challenging task that often requires the understanding of the specific interactions established between the porous framework and the gases. Here we propose an approach to obtain an enhanced selectivity based on the use of compartmentalized coordination polymers, named CCP-1 and CCP-2, which are crystalline materials comprising isolated discrete cavities. These compartmentalized materials are excellent candidates for the selective separation of CO2 from methane and nitrogen. A complete understanding of the sorption process is accomplished with the use of complementary experimental techniques including X-ray diffraction, adsorption studies, inelastic- and quasi-elastic neutron scattering, magnetic measurements and molecular dynamics calculations.

Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene.

The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

Paving the way for methane hydrate formation on metal-organic frameworks (MOFs).

The presence of a highly tunable porous structure and surface chemistry makes metal-organic framework (MOF) materials excellent candidates for artificial methane hydrate formation under mild temperature and pressure conditions (2 °C and 3-5 MPa). Experimental results using MOFs with a different pore structure and chemical nature (MIL-100 (Fe) and ZIF-8) clearly show that the water-framework interactions play a crucial role in defining the extent and nature of the gas hydrates formed. Whereas the hydrophobic MOF promotes methane hydrate formation with a high yield, the hydrophilic one does not. The formation of these methane hydrates on MOFs has been identified for the first time using inelastic neutron scattering (INS) and synchrotron X-ray powder diffraction (SXRPD). The results described in this work pave the way towards the design of new MOF structures able to promote artificial methane hydrate formation upon request (confined or non-confined) and under milder conditions than in nature.