Extraframework Sites Research Articles

Robust palladium oxide nano-cluster catalysts using atomic ions and strong interactions for high-performance methane oxidation

Optimizing metal catalyst structures to achieve desired states is vital for efficient surface reactions, yet remains challenging due to the lack of well-defined precursor materials and weak metal-support interaction. Palladium-based catalysts, when not properly tailored for complete methane oxidation exhibit insufficient performance. Herein, we fabricate Pd oxide nano-clusters supported on SSZ-13 using atomic ions with strong metal-support interaction (SMSI). Steam treatment of Pd/SSZ-13 transforms Pd particles into ions and induces SMSI. Subsequently, CO reduction and O2 oxidation yield mildly sintered Pd oxide nano-clusters firmly anchored on extra-framework Alpenta sites of SSZ-13, facilitating superior activity. The robustness from SMSI prevents irreversible deactivation, and water-resistance by complete dehydration suppresses reversible degradation in wet conditions. This catalyst exhibits high performance in bench-scale reactions using monolith catalysts, ensuring applicability for industrial methane abatement. The results demonstrate that sequential treatment to Pd/SSZ-13 offers a promising approach for tailoring metal structures to enable high-performance methane oxidation.

Plumbogaidonnayite, PbZrSi3O9⋅2H2O, a new Pb-member of the gaidonnayite group from the Saima alkaline complex, Liaoning Province, China

AbstractPlumbogaidonnayite, ideally PbZrSi3O9⋅2H2O, is a new gaidonnayite-group mineral discovered as a secondary product derived from the alteration of eudialyte from the Saima alkaline complex, China. It occurs as aggregates (up to 1 mm) composed of subhedral to anhedral or platy crystals (individually 5–50 μm), associated closely with microcline, natrolite, aegirine, gaidonnayite, georgechaoite, zircon, bobtraillite and britholite-(Ce) in eudialyte pseudomorphs. The crystals are transparent, colourless or light brown with a vitreous lustre. Plumbogaidonnayite is brittle with conchoidal fracture, and it has a Mohs hardness of ~5 and a calculated density of 3.264 g/cm3. It is optically biaxial (+) with α = 1.61(3), β = 1.63(3) and γ = 1.66(4). The calculated 2V is 80°, with the optical orientations X, Y and Z parallel to the crystallographic a, b and c axes, respectively. The empirical formula is (Pb0.70Ca0.17Ba0.01K0.11Na0.01Y0.01)Σ1.01(Zr1.00Hf0.01Ti0.01)Σ1.02Si3.01O9⋅2H2O calculated on the basis of nine oxygen atoms per formula unit and assuming the occurrence of two H2O groups. Plumbogaidonnayite is orthorhombic, P21nb, a = 11.7690(4) Å, b = 12.9867(3) Å, c = 6.66165(16) Å, V = 1018.17(5) Å3 and Z = 4. The nine strongest lines of its powder XRD pattern [d in Å (I, %) (hkl)] are: 6.489 (36) (020), 5.803 (100) (101), 4.661 (27) (021), 4.336 (29) (121), 3.640 (30) (221), 3.114 (79) (112), 2.947 (27) (400), 2.622 (27) (241) and 2.493 (27) (312). Plumbogaidonnayite has a similar spiral chain framework structure with gaidonnayite and georgechaoite, which is composed of SiO4 tetrahedra and ZrO6 octahedra, but with disordered extra-framework sites (cations and H2O groups) characterised by the substitution of 2Na+ (K+)→Pb2+ (Ca2+) + □ (vacancy). The discovery of plumbogaidonnayite adds a new perspective on the cation ordering and heterovalent substitution mechanism in gaidonnayite-group minerals.

Propane dehydrogenation on an extra-framework and framework-embedded metal site within ZSM-5 zeolite from first-principles microkinetic simulations

The Lewis acid sites in ZSM-5 zeolite involving Co, Ni, and Cu cations were computationally studied on the stability and the PDH catalytic activity.

Novel “Anti-Zeolite” Ba3Sr3B4O12: Eu3+ Phosphors: Crystal Structure, Optical Properties, and Photoluminescence

Novel Ba3Sr3B4O12: Eu3+ phosphors were synthesized by crystallization from a melt. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) solid solutions were refined from SCXRD data. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 phosphors can be described in terms of the cationic sublattice and belong to the “anti-zeolite” family of borates. Its cationic framework is constructed of Ba and Sr atoms. The Eu3+ ions occupy the Sr(1) extraframework cationic site in the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01–0.20) phosphors. The Ba3Sr2.625Eu0.25B4O12 borate crystallizes in a new structure type (I4/mcm, a = 13.132(3), c = 14.633(4) Å, V = 2523.5(11) Å3, Z = 8, R1 = 0.067). In the Ba3Sr2.625Eu0.25B4O12 crystal structure, the Eu3+ ions occupy Sr(1) and Ba/Sr(1) sites, which leads to changes in the crystal structure. The Wyckoff letter and occupancy of the O(5) site are changed; B–O anion groups contain two BO3 triangles (B(3) and B(4)), orientationally disordered over the four orientations, and two ordered BO3 triangles (B(1) and B(2)) in contrast to Ba3Sr3B4O12, in which these groups are disordered over the 4 and 8 orientations. The emission spectra of Ba3Sr3B4O12: Eu3+ show characteristic lines corresponding to the intraconfigurational 4f-4f transitions of Eu3+ ions. Ba3Sr2.7Eu0.20B4O12 demonstrates the strongest luminescent intensity among Ba3(Sr3−1.5xEux)B4O12 solid solutions. The increase in the Eu3+ content results in a gradual change in chromaticity from light red to orange-red/red. It can be concluded that Ba3Sr3B4O12: Eu3+ is a promising red phosphor.

Magnetic coupling of divalent metal centers in postsynthetic metal exchanged bimetallic DUT-49 MOFs by EPR spectroscopy

EPR measurements at X- (9.5 GHz), Q- (34 GHz) and W-band (94 GHz) on paddlewheel (PW) type post-synthetic metal exchanged DUT-49(M,M): M- Zn, Mn, Cu MOFs are here reported (DUT–Dresden University of Technology). Temperature-dependent X-band measurements are recorded from T = 7 K to T = 170 K on monometallic DUT-49(Cu), DUT-49(Mn), and bimetallic DUT-49(Cu0.7Zn0.3), DUT-49(Cu0.5Mn0.5) MOFs. In the case of the CuII - CuII dimers in DUT-49(Cu), an isotropic exchange coupling of the metal ions (2J = −240(11) cm−1) determined from the EPR intensity of the S = 1 spin state of the CuII–CuII dimers using the Bleaney Blowers equation. The sign of the found isotropic exchange coupling constant confirms an antiferromagnetic coupling between the cupric ions. Also, the MnII ions in the paddle wheels of DUT-49(Mn) are antiferromagnetically coupled. However, at low temperatures, EPR measurements reveal the presence of CuII and MnII monomers in DUT-49(Cu) and DUT-49(Mn), respectively, either associated with extra framework sites or defective paddle wheels. Otherwise, EPR signals observed for bimetallic DUT-49(Cu0.7Zn0.3) and DUT-49(Cu0.5Mn0.5) MOFs reveal the formation of mixed ion CuII–ZnII and CuII–MnII paddle wheels with SCuZn =1/2 and SCuMn = 2 spin states, respectively.

Concerning the incorporation of potassium in the crystal structure of combeite (Na2Ca2Si3O9)

Potassium incorporation in the structure of combeite has been studied in detail. Since natural combeites are known to contain only small amounts of potassium focus was laid on the Na-rich part of a hypothetical solid-solution series with composition Na2-xKxCa2Si3O9. Samples were prepared from mixtures of silica and the corresponding carbonates for nominal compositions with x = 0.2, 0.3 and 0.5, heated from ambient temperature to 1350 °C and slowly cooled to 1000 °C. After disintegration of the carbonates, the platinum capsules used as sample containers were welded shut in order to avoid losses of the volatile K2O and Na2O components. From all three batches potassium containing combeite crystals could be retrieved. Single-crystal diffraction experiments revealed the following compositions: Na2.10(1)K0.11(1)Ca1.90(1)Si3O9, Na2.09(1)K0.18(1)Ca1.91(1)Si3O9 and Na2.13(1)K0.18(1)Ca1.87(1)Si3O9. Consistently, the trigonal crystals (space group P 31 2 1) contained (i) (K + Na):Ca ratios larger than 1:1 and (ii) potassium concentrations lower than those in the starting mixtures. Since the K-contents of the samples obtained from the runs with x = 0.3 and 0.5 were almost identical, the solid-solution seems to be rather limited with an upper boundary of about one potassium atom per unit cell. The structure of the K-containing combeites is very close to the K-free structures reported in the literature. It can be described as a mixed tetrahedral-octahedral network in which additional K, Na and Ca cations are incorporated for charge compensation. A detailed analysis of the topological features of the net is presented. From the six observed extra-framework sites only the M22 position showing a coordination environment with ten next oxygen neighbours is involved in the K-substitution. Potassium uptake is also reflected in increasing values for the lattice parameters a and c as well as the unit-cell volumes. Actually, the c-axis is more affected from the incorporation of the comparatively large K+-cations.

Stable and Uniform Extraframework Cations in Faujasite Zeolites.

Extraframework transition metal ions (TMIs) in zeolites can serve as active sites for adsorption and catalysis. However, due to the complexity and mobility of extraframework cation sites, their applications are significantly limited and the structure-performance relationship is poorly understood. In this Perspective, stable and uniform TMIs in zeolites are exemplified and their characteristics are discussed. A series of TMIs can be introduced to specific cation sites of faujasite via a ligand-protected in situ synthesis route to construct uniform TMIs in the zeolite matrix, namely, TMI@FAU (TMI= Co, Ni, Cu, Rh, and Pt). Coordinatively unsaturated TMIs within faujasite are active for small-molecule adsorption and activation, and therefore, TMI@FAU zeolites show unique properties in adsorption and catalysis. TMI@FAU zeolites appear to be ideal model systems, and the well-defined structure of TMI@FAU greatly facilitates the mechanism studies by spectroscopic investigations and theoretical simulations.

Mixed (Ag+, Ca2+)-LTA zeolite with suitable pore feature for effective separation of C3H6/C3H8

Separating C3H6/C3H8 is a challenging task owing to their similar sizes and boiling points. In this study, we report a sequential and partial Ag+/Ca2+ ion-exchanged zeolite that exhibits ideal C3H6/C3H8 molecular sieving. Moreover, the zeolite exhibited superior C3H6 uptake of 2.37 mmol/g and molecular packing density (∼77% packing of liquid C3H6) at an extremely high C3H6: Ag+ ratio of 21.5 with Ag content as low as 1.18 wt%. The (Ag+, Ca2+) cations were sequentially exchanged into LTAs by comprehensively considering the extra-framework cation distribution and site preferences for different cations. By exchanging Ag+ with Na+ in the extra-framework of LTA, C3H6 can be admitted even at the average LTA apertures of sizes < 4 Å. Meanwhile, exchanged Ag+ also increased the adsorption kinetics of C3H6 by an order of magnitude. Hydrophobic modification on Ca-Ag-LTA was successfully achieved to significantly suppress the competition from water while retaining excellent regenerability in multiple cycles. The strategy of binary ion exchange to delicately tune the pore channels and chemistry and selectively admit molecules with beneficial kinetics might potentially be broadened to other industrial separation processes.

Property-activity relations of multifunctional reactive ensembles in cation-exchanged zeolites: a case study of methane activation on Zn2+-modified zeolite BEA.

The reactivity theories and characterization studies for metal-containing zeolites are often focused on probing the metal sites. We present a detailed computational study of the reactivity of Zn-modified BEA zeolite towards C-H bond activation of the methane molecule as a model system that highlights the importance of representing the active site as the whole reactive ensemble integrating the extra-framework ZnEF2+ cations, framework oxygens (OF2-), and the confined space of the zeolite pores. We demonstrate that for our model system the relationship between the Lewis acidity, defined by the probe molecule adsorption energy, and the activation energy for methane C-H bond cleavage performs with a determination coefficient R2 = 0.55. This suggests that the acid properties of the localized extra-framework cations can be used only for a rough assessment of the reactivity of the cations in the metal-containing zeolites. In turn, studying the relationship between the activation energy and pyrrole adsorption energy revealed a correlation, with R2 = 0.80. This observation was accounted for by the similarity between the local geometries of the pyrrole adsorption complexes and the transition states for methane C-H bond cleavage. The inclusion of a simple descriptor for zeolite local confinement allows transferability of the obtained property-activity relations to other zeolite topologies. Our results demonstrate that the representation of the metal cationic species as a synergistically cooperating active site ensembles allows reliable detection of the relationship between the acid properties and reactivity of the metal cation in zeolite materials.

Confinement in a Zeolite and Zeolite Catalysis.

ConspectusZeolites, accompanied by their initial discovery as natural mines and the subsequent large-scale commercial production, have played indispensable roles in various fields such as petroleum refining and the chemical industry. Understanding the characteristics of zeolites, in contrast to their counterparts with similar chemical compositions and the origin thereof, is always a hot and challenging topic. Zeolites are known as intrinsic confined systems with ordered channels on the molecular scale, and structural confinement has been proposed to explain the unique chemical behaviors of zeolites. Generally, the channels of zeolites can regulate the diffusion of molecules, leading to a visible difference in molecular transportation and the ultimate shape-selective catalysis. On the other hand, the local electric field within the zeolite channels or cages can act on the guest molecules and change their energy levels. Confinement can be simply interpreted from both spatial and electronic issues; however, the nature of zeolite confinement is ambiguous and needs to be clarified.In this Account, we make a concise summary and analysis of the topics of confinement in a zeolite and zeolite catalysis from two specific views of spatial constraint and a local electric field to answer two basic questions of why zeolites and what else can we do with zeolites. First, it is shown how to construct functional sites including Brønsted acid sites, Lewis acid sites, extraframework cation sites, and entrapped metal or oxide aggregates in zeolites via confinement and how to understand the specific role of confinement in their reactivity. Second, the multiple impacts of confinement in zeolite-catalyzed reactions are discussed, which rationally lead to several unique processes, namely, Brønsted acid catalysis confined in zeolites, Lewis acid catalysis confined in zeolites, catalysis by zeolite-confined coordinatively unsaturated cation sites, and a cascade reaction within the confined space of zeolites. Overall, confinement effects do exist in zeolite systems and have already played extremely important roles in adsorption and catalysis. Although confinement might exist in many systems, the confinement by zeolites is more straightforward thanks to their well-ordered and rigid structure, deriving unique chemical behaviors within the confined space of zeolites. A zeolite is a fantastic scaffold for constructing isolated sites spatially and electrostatically confined in its matrix. Furthermore, zeolites containing well-defined transition-metal sites can be treated as inorganometallic complexes (i.e., a zeolite framework as the ligand of transition-metal ions) and can catalyze reactions resembling organometallic complexes or even metalloenzymes. The local electric field within the confined space of zeolites is strong enough to induce or assist the activation of small molecules, following the working fashion of frustrated Lewis pairs. The tactful utilization of structural confinement, both spatially and electronically, becomes the key to robust zeolites for adsorption and catalysis.

Determination of Zn Speciation, Siting, and Distribution in Ferrierite Using Luminescence and FTIR Spectroscopy

A methodology for the analysis of the siting of Zn2+ ions in extra-framework cationic sites of silicon-rich zeolite was developed and demonstrated on Zn-ferrierite samples (Si/Al 8.5, Zn/Al 0.04–0....

Insight into tri-coordinated aluminum dependent catalytic properties of dealuminated Y zeolites in oxidative desulfurization

Aluminosilicate zeolite as a versatile material is of great importance for industrial catalysis, whose noumenal Brønsted and Lewis acid sites generally determine the activity, selectivity, and even stability during the catalytic reactions. Unlike well-studied Brønsted acid sites for acid-catalyzed reactions, the pending question about the effectiveness and role of Lewis acid sites derived from framework-associated and/or extra-framework aluminum in selective oxidation reactions remains unanswered. Herein, tri-coordinated Al was rationally constructed via precisely tailoring acid-treatment time for ultra-stable Y zeolite, which was associated with Lewis acidity. This Lewis acid sites rather than extra-framework related Lewis acid sites were confirmed to be the catalytic active sites for oxidative desulfurization with hydrogen peroxide as oxidant. Additionally, the Al evolution mechanism and physicochemical properties for dealumination-derived samples were systematically investigated via series of techniques. The most possible tri-coordinated Al micro-structure with Lewis acidity was verified by density functional theory calculations. More importantly, the superoxide and hydroxyl radical were both the active oxygen species during the catalytic reactions. This work discloses the decisive effectiveness of framework-associated Al species with Lewis acidity in zeolites to oxidative desulfurization and paves a straightforward way for rationally designing Lewis acidic Al-zeolite catalysts.

A highly hydrated variety of elpidite from the Khibiny alkaline complex, Kola Peninsula, Russia

AbstractAn unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na2ZrSi6O15⋅3H2O, in its crystal chemical features, infrared spectrum and optical characteristics. The chemical composition (wt.%, electron microprobe, H2O by TGA) is: Na2O 5.45, K2O 0.67, CaO 0.05, SiO2 60.32, TiO2 1.34, ZrO2 18.43, Nb2O5 0.65, H2O 12.80, total 99.71. The empirical formula calculated on the basis of 6 Si and 15 O atoms is [(Na1.05K0.08Ca0.01)Σ1.14(H3O)0.74]Σ1.88(Zr0.89Ti0.10Nb0.03)Σ1.02Si6O15⋅3.47H2O; the H2O:H3O ratio was calculated from the charge balance requirement, taking into account the results of crystal structure refinement. The highly hydrated variety of elpidite is orthorhombic, Pma2, a = 14.5916(6), b = 7.3294(3), c = 7.1387(2) Å, V = 763.47(5) Å3 and Z = 2. The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 3.43%. The structure is based upon an elpidite-type heteropolyhedral Zr–Si–O framework with Na+ and H3O+ cations and H2O molecules in the zeolitic channels. Hydronium cations substitute for water molecules in one of the extra-framework sites. This variety of elpidite could be considered as an intermediate product of natural ion-exchange reaction between ‘ordinary’ elpidite and a low-temperature hydrothermal fluid.

Ab initio screening of zeolite Y formulations for efficient adsorption of thiophene in presence of benzene

In the context of deep desulfurization of transport fuels, the present work aimed at identifying a suitable material for the selective removal of thiophene from fuels. Dispersion corrected density functional theory (DFT) calculations have been carried out in order to investigate the adsorption of benzene and thiophene in various faujasite zeolite formulations including DAY, HY, LiY, NaY, KY, CsY, Cu(I)Y, Cu(II)Y, Ag(I)Y, Zn(II)Y, and FAU containing Lewis acid sites (LAS) (defect or extra-framework). Bearing-LAS FAU, Cu(I)Y, Cu(II)Y, Zn(II)Y, CsY, and HY showed a higher affinity towards thiophene adsorption. In particular, thiophene is more adsorbed on defect LAS than benzene by 17.7 kJ/mol, suggesting that this zeolite could be chosen as a suitable candidate for the optimal selective adsorption of thiophene in the presence of benzene. In terms of regenerability, all formulations can be safely used (except the one containing extra-framework Lewis acid sites) as they can limit the activation of the C-S bond of thiophene. Considering both adsorption selectivity and sorbent regenerability criteria, faujasites containing defect Lewis acid sites could be chosen as a good compromise to perform a selective adsorption of thiophene in presence of benzene.

Spectroscopic Signature of Lewis Acidic Framework and Extraframework Sn Sites in Beta Zeolites

A variety of Sn-containing Beta zeolites possessing framework or extraframework Sn sites were prepared by a two-step postsynthesis procedure. The nature of these Sn species was systematically inves...

Spectroscopic investigations on structural incorporation pathways of FeIII into zeolite frameworks in cement-relevant environments

FeIII-containing aluminosilicate zeolites are present in cement-relevant and natural environments. Although FeIII is known to occur in framework tetrahedral sites where it substitutes isomorphically AlIIIO4 or in extra-framework octahedral sites as free Fe(H2O)63+, the structural incorporation process of FeIII into different sites is little known. We aim to discern feasible pathways of FeIII incorporation using hydrothermal synthesis methods and synchrotron-based spectroscopic analyses. Results showed that introducing either Fe3+ or Fe2O3·xH2O initially during zeolite nucleation did not lead to FeIII incorporation into the zeolites but only Fe2O3·xH2O prevailed in both cases. However, Fe(NO3)3, FeCl3, and Fe2O3·xH2O affected the kind of zeolite formed. A feasible pathway to incorporate tetrahedral FeIII in the zeolite framework was to introduce firstly FeIII in the cage of faujasite-Y followed by a phase transformation to chabazite. This study facilitates understanding of FeIII uptake in zeolites and of FeIII functional sites that can contribute to immobilization of contaminants.

Dehydration behavior of a natural hydrated Ca-chabazite studied by in-situ high-temperature single-crystal X-ray diffraction

Abstract Dehydration behavior of a natural hydrated Ca-chabazite with composition (Ca1.57Na0.49)(Al3.39Si8.55)O24·12.47H2O has been studied by the structure analyses based on the in-situ high-temperature single-crystal X-ray diffraction data at 100, 200 and 250 °C. Among the five water sites (OW1–OW5) and four exchangeable-cation sites (Ca1–Ca4) found previously in the room-temperature (RT) structure, the present structure analyses revealed the presence of OW1, OW4, Ca3 sites at 100 °C and of OW3, Ca3, Ca4 sites at 200 and 250 °C. The presence of the new extraframework sites was also revealed: OW2’ site at 100 °C and Ca5 site at 200 and 250 °C. From the temperature dependence of the occupation for these extraframework sites, the dehydration and cation migration processes are summarized and rationalized as follows. With heating up to 100 °C, OW3 water molecules, having no bonds to exchangeable cations, are completely desorbed. Simultaneously, Ca1 and Ca2 cations lose the large amounts of water molecules as ligands (OW1 and OW5 for Ca1, OW4 for Ca2); this brings about the simultaneous migration of both cations to adjacent Ca3 site, surrounded by more ligands. With further heating up to 250 °C, OW2’ water molecules, having no bonds to exchangeable cations, are completely desorbed. Simultaneously, most of the Ca3 cations migrate to adjacent Ca4 and Ca5 sites by losing the large amounts of water molecules as ligands (OW1, OW4). A part of the water molecules desorbed in the temperature range of 100–250 °C migrate to OW3 site to be bonded to the remaining Ca3 cations. The peculiar temperature dependence of Si/Al−O1, −O2 and −O3 bond lengths in the framework structure can be explained in terms of their bond-valence variations due to such dehydration and cation migration processes. On the other hand, the variation of Si/Al−O4 bond length is dominated by thermal expansion effect rather than the bond valence effect.

On the impact of copper local environment on hydrogen sulfide adsorption within microporous AlPO4-5

This work aims at elucidating the most active modes of copper incorporation towards H2S adsorption. Various synthesis methodologies were followed, notably, incorporation via isomorphic substitution, liquid ion exchange (LIE), vapor phase ion exchange (VIE), and nanoparticles inclusion during hydrothermal synthesis, for the introduction of copper into AlPO4-5 and SAPO-5. Techniques such as XRD and SEM/EDX, TEM, FT-IR and N2 adsorption-desorption were employed to characterize the synthesized materials. The Cu- containing materials were examined as sorbents for H2S removal via breakthrough experiments at 150 °C. The highest sulfur removal capacity was attained over the CuO nanoparticles supported in AlPO4-5 (10 % CuO/AlPO4-5), followed by a copper-based material prepared by VIE (Cu-VIE-0.2), accounting for H2S breakthrough capacities of 0.31 and 0.17 mmol ∙ g−1, respectively. The superior performance of these two materials could be ascribed to the relatively higher copper loading in the form of CuO as confirmed by XRD. Comparing the capacity per gram of active site, it was revealed that positioning Cu ions in extra-framework sites leads to an order of magnitude enhancement. This can be attributed to the possibility of a Cu ion to interact with more than one H2S molecule simultaneously unlike the other incorporation modes examined. Furthermore, copper ions incorporated into the crystal framework were found to be inactive towards H2S adsorption.

Mineralogical dataset of natural zeolites from Lessini Mounts, Northern Italy: Analcime, natrolite, phillipsite and harmotome chemical composition.

This dataset article contains mineralogical and chemical data of some natural zeolites such as analcime, natrolite, phillipsite and harmotome. These minerals were found as secondary phases within vesicles and veins in the basaltic rocks of the Lessini Mounts, Northern Italy. Methods for obtaining the datasets include optical microscopy, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Analcime forms well-developed, transparent to milky crystals with a typical icositetrahedron habit. The average composition of analcime is calculated as Na13.79Ca0.01K0.03Ba0.03[Al14.28Si33.82O96] 16H2O, with all of the extra-framework sites occupied by sodium. Natrolite usually forms hemispherical aggregates with glassy, colourless to white thin prismatic crystals, which generally radiate from a central point. The average chemical composition of natrolite is Na14.28Ca0.14K0.01[Al15.60Si24.59O80] 16H2O. Crystals of phillipsite-harmotome serie occur in a variety of forms and display a highly variable chemical composition, from almost pure compositions to intermediate values. Phillipsite is more common and its average chemical composition is Ca1.40Na0.29K1.08Ba0.27[Al4.68Si11.28O32] 12H2O, while harmotome is rare and has an average chemical composition of Ca0.97Na0.20K0.36Ba0.91[Al4.60Si11.46O32] 12H2O. The obtained dataset can be used for various purposes: it can be used by other authors to compare morphological features and chemical compositions of similar zeolites crystals discovered in other parts of the world, it can be compared with those obtained from similar geologic environments encouraging studies on hydrothermal processes, and it could represent the starting point for a potential exploration of zeolites from an industrial point of view.

Small Crown-Ether Complexes as Molecular Models for Dihydrogen Adsorption in Undercoordinated Extraframework Cations in Zeolites

1:1 metal complexes of small crown-ethers are structurally similar to extraframework sites in metal-exchanged zeolites. Using ab initio calculations, we show that adsorbed molecular hydrogen follow...