Natural methane hydrates are believed to be the largest source of hydrocarbons on Earth. These structures are formed in specific locations such as deep-sea sediments and the permafrost based on ...demanding conditions of high pressure and low temperature. Here we report that, by taking advantage of the confinement effects on nanopore space, synthetic methane hydrates grow under mild conditions (3.5 MPa and 2 °C), with faster kinetics (within minutes) than nature, fully reversibly and with a nominal stoichiometry that mimics nature. The formation of the hydrate structures in nanospace and their similarity to natural hydrates is confirmed using inelastic neutron scattering experiments and synchrotron X-ray powder diffraction. These findings may be a step towards the application of a smart synthesis of methane hydrates in energy-demanding applications (for example, transportation).
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-butanediylbistris(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 β = 90.22°. The topology of ITQ-52 can be described as a replication of a composite building unit with ring notation 435461 that gives rise to the formation of an interconnected 8R and 10R channel system.
Shining bright: Porous metal–organic framework materials are important owing to their potential applications as sensors. A new family of nanoporous, multifunctional rare‐earth metal–organic materials ...displays emission quantum yields and efficiencies that are the highest reported for solid‐state Eu3+ compounds with organic ligands and magnetic properties. The picture shows Gd,Eu‐ and Tb‐containing materials under UV light and interacting with a magnet.
Zeolite Rho is able to successfully separate CO(2) from CH(4) with the highest selectivity ever observed on the basis of pore diameter and surface polarity. The adsorption of CO(2) provokes ...structural changes in the zeolite Rho.
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.
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.
ITQ‐69 has been synthesized, characterized, and its application as selective adsorbent for light olefins/paraffins has been tested.
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.
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.
As organic structure‐directing agents: Tetraalkylarsonium cations, a novel member of the ‐onium (ammonium, phosphonium, and sulfonium) family of organic structure‐directing agents for the synthesis of zeolites, are presented for the first time. These cations permit the synthesis of the zeolite ZSM‐5 as well as serving as probes for the study of the zeolite and the occluded cation by several techniques, as powder XRD, solid‐state NMR spectroscopy, and XAS.
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.
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 Co 2 -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 Co 2 -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 Co 2 -MOF in an alcoholic solution of Nafion gives rise to a composite (Co 2 -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.
PDF
