Thermal behaviour of siliceous faujasite: further structural interpretation of negative thermal expansion

The high-temperature behaviour of siliceous faujasite (Si-Y) was investigated by in situ synchrotron Xray powder diffraction from room temperature up to 1123 K. This porous phase is remarkably stable when heated, and no phase transitions or changes in symmetry are observed. A marked negative thermal expansion (NTE), already reported in literature for a heating range from 25 to 573 K, was confirmed up to about 923 K. Above this temperature a positive thermal expansion was observed. Si-Y’s thermal behaviour was interpreted on the basis of the transverse thermal vibrations of the oxygen atoms involved in the T–O–T linkages and a series of other structural features characterizing the faujasite structure, namely the T–T distances between adjacent tetrahedral sites, the thickness of the double 6-membered rings, and the ditrigonal index of the 6-membered rings. Moreover, the thermal behaviour of several other anhydrous porous materials with NTE behaviour is discussed and compared to that of Si-Y

High-pressure behavior of high silica ferrierite

Ferrierite (FER framework topology) is a well-known aluminosilicate zeolite mineral. An understanding of the structure and properties of FER remains important because of its role as a catalyst in commercial reactions. For example, it is important in the petrochemical industry, where it has been used as a shape selective catalyst for the production of isobutene. The thermal behavior of this phase (in its high silica form) was recently studied by Bull et al [1], while its compressibilty has never been investigated before. The high pressure (HP) behavior of synthetic high silica zeolite ferrierite (FER) was investigated by means of in-situ synchrotron X-ray powder diffraction, with the aim to understand the P-induced deformation mechanism. The microporous material was sinthesized starting from pure silica and pyridine and propyl-amine as structure directing agents. Here we report the preliminary results on the compressibility of the as synthesized phase. The study of the compressibility of the calcined one will be carried out in the following steps of the project.The crystal structure of ferrierite is built up of rings of fivecornershared SiO4 tetrahedra (known as five-membered ringsor 5MRs) building units, which form layers in the ab plane.The layers are connected to form a matrix of 10MR channels running parallel to the c axis, which are intersected by 8MR channels running parallel to the b axis. Six-membered rings connect the 10MRs alongthe c axis direction. The HP diffraction experiments were performed at BM01a beamline (ESRF), at the fixed wavelength of 0.71 Å, using a modified Merril- Basset DAC and a mixture of methanol- ethanol and water (16:3:1) as penetrating P-transmitting medium. The powder patterns were collected from Pamb to 6.2 GPa. Some patterns were also measured upon pressure release up to Pamb, to check the reversibility of the compression effects. The unit cell parameters were refined by means of Rietveld method. The main results of this study are: 1) No complete X-ray amorphization is observed up to about 6.6 GPa; 2) No abrupt change of the elastic behavior is observed in the whole pressure range. Between Pamb and 6.2 GPa the reduction of the cell parameter are 4%, 5% and 6% for a, b and c respectively, accounting for a volume reduction of about 14 %. 3) The bulk modulus obtained using a second order Birch-Murnaghan equation of state and data weighted by the uncertainties in P and V was K0 = 30.1(3) GPa. This compressibility determined in m.e.w. is one of the highest when compared with other natural and synthetic zeolites studied with “penetrating” aqueous media [2], [3]. 4) The P-induced effects on as-syntehsized ferrierite structure are completely reversible

Compressibility behaviour of as-synthesized high-silica Ferrierite.

Ferrierite (FER framework topology) is a well-known aluminosilicate zeolite mineral. An understanding of the structure and properties of FER remains important because of its role as a catalyst in commercial reactions. For example, it is important in the petrochemical industry, where it has been used as a shape selective catalyst for the production of isobutene. The thermal behavior of this phase (in its high silica form) was recently studied by Bull et al [1], while its compressibilty has never been investigated before. The high pressure (HP) behavior of synthetic high silica zeolite ferrierite (FER) was investigated by means of in-situ synchrotron X-ray powder diffraction, with the aim to understand the P-induced deformation mechanism. The microporous material was synthesized starting from pure silica and pyridine and propyl-amine as structure directing agents. Here we report the preliminary results on the compressibility of the as-synthesized phase. The study of the compressibility of the calcinated one will be carried out in the following steps of the project. The crystal structure of ferrierite is built up of rings of fivecorner-shared SiO4 tetrahedra (known as five-membered ringsor 5MRs) building units, which form layers in the ab plane. The layers are connected to form a matrix of 10MR channels running parallel to the c axis, which are intersected by 8MR channels running parallel to the b axis. Six-membered rings connect the 10MRs alongthe c axis direction. The HP diffraction experiments were performed at BM01a beamline (ESRF), at the fixed wavelength of 0.71 Å, using a modified Merril-Basset DAC and a mixture of methanol:ethanol:water (16:3:1) as P-transmitting medium. The powder patterns were collected from Pamb to 6.2 GPa. Some patterns were also measured upon pressure release up to Pamb, to check the reversibility of the compression effects. The unit cell parameters were refined by means of Rietveld method. The main results of this study are: 1) No complete X-ray amorphization is observed up to about 6.6 GPa; 2) No abrupt change of the elastic behavior is observed in the whole pressure range. Between Pamb and 6.2 GPa the reduction of the cell parameter are 4%, 5% and 6% for a, b and c respectively, accounting for a volume reduction of about 14 %. 3) The P-induced effects on the as-synthesized Si-ferrierite cell parameters are completely reversible. 4) The bulk modulus obtained using a second order Birch-Murnaghan equation of state and data weighted by the uncertainties in P and V was K0 = 30.1(3) GPa. This compressibility is one of the highest when compared with the other natural and synthetic zeolites studied with “penetrating” aqueous media [2, 3] and is very similar to that of SAPO-34 [4], another microporous material studied at HP in its as-synthesized form containing the organic template

Elastic behavior and high pressure-induced phase transition in chabazite: new data from a sample from Nova Scotia

Recently, the high pressure (HP) behavior of a natural chabazite from Vallerano [1] (VALL), and on the synthetic phases SAPO-34 [1] and ALPO-34 [2], was investigated in the frame of a wider project aimed at understanding the role of the framework/extraframework content on the compressibility of CHA-type porous materials. In this work, further structural information is obtained studying the response to HP of another natural chabazite sample from Nova Scotia (Canada) (NS) (s.g. R-3mR [3]), characterized by a different chemical composition with respect to VALL. The study was performed by means of in situ synchrotron X-ray powder diffraction (XRPD) and silicone oil as non-penetrating P-transmitting medium. XRPD experiments were performed in DAC at the BM01 beamline at ESRF (Grenoble, France) with a fixed =0.7355 Å. Powder patterns were collected from Pambup to 8.6 GPa and upon decompression. All the features of the Pamb pattern and the unit cell parameters are well recovered upon P release. Below 2.1 GPa, a and cell parameters slightly decrease and increase respectively with a resulting volume reduction of 3.6 %. Above 2.1 GPa, a transition to a triclinic P-1 pseudo-rhombohedral phase is observed. The rhombohedral to triclinic phase transition is accompanied by an abrupt decrease in the unit cell parameters and in the unit cell volume ( V=-4.0%). Between 2.5 and 5.9 GPa, the triclinic/pseudo-rhombohedral cell parameters decrease regularly and the unit cell volume variation ( V=-3.0%) indicates a lower compressibility with respect to that observed before the transition. In the highest P regime (5.9-7.2 GPa), a further slope change, with an increase in compressibility, is observed. As a whole, V between Pamb and 7.2 GPa is -12.6%. The elastic parameters, calculated with a second order BM-EoS, are V0 = 826 (1) Å3, K0 = 54(3) GPa and V0 = 784(2) Å3, K0 = 91(5) GPa, for the rhombohedral and triclinic phase, respectively. Preliminary results from Rietveld refinements up to about 1 GPa, suggest that the deformation mechanism acting in the low-P regime is a cooperative tilting of the tetrahedra belonging to the double 6-ring – resulting in a decrease of its thickness – accompanied by a simultaneous di-trigonalization of the two 6-rings. A similar mechanism was previously observed during compression of levyne [4]. The HP-induced cell volume contraction of NS (12.6 %) is higher than that of VALL (10.3%) in the same P range. This is congruent with the lower content in large extraframework potassium cations of NS, which contribute to sustain the porous structure in VALL

A new framework topology in the dehydrated form of zeolite levyne.

0003-004X/13/1112\u20132063$05.00/DOI: http://dx.doi.org/10.2138/am.2013.4583 2063 A new framework topology in the dehydrated form of zeolite levyne Rossella Arletti1, Giovanna Vezzalini2, Simona Quartieri3, Fernando C\ue1mara1 and Matteo Alvaro4,* 1Dipartimento di Scienze della Terra, Universit\ue0 di Torino, via Valperga Caluso n. 35, 10125 Torino, Italy 2Dipartimento di Scienze Chimiche e Geologiche, Universit\ue0 di Modena e Reggio Emilia, via Giuseppe Campi, 183, 41125 Modena, Italy 3Dipartimento di Fisica e Scienze della Terra, Universit\ue0 di Messina, Viale F. Stagno D\u2019Alcontres, 31, 98122 Messina, Italy 4Dipartimento di Scienze della Terra e dell\u2019Ambiente, Universit\ue0 degli Studi di Pavia, Italy; and International Research School of Planetary Sciences, Universit\ue0 G. d\u2019Annunzio, Chieti, Italy A bstract The thermoelastic behavior and structural evolution of a natural levyne-Ca [(Ca7.8 Na2.2K1.1)\u3a311.1 Al20.0Si34.2O108 c551.5H2O; R3m; a = 13.377(4) \uc5, c = 22.870(1) \uc5, V = 3544.1(3) \uc53] were studied by both T-resolved synchrotron X\u2011ray powder diffraction (SR-XRPD) between room temperature and 800 \ub0C, and by conventional-source high-temperature single-crystal X\u2011ray diffraction (SC-XRD). Above 230 \ub0C, water loss and reallocation of extraframework cations induce the straining and consequent breaking of T-O-T bridges in the D6R, with resulting migration of tetrahedral cations to new tetrahedral sites. The new tetrahedra share an edge with the previously occupied tetrahedra. This phenomenon gives rise to a new topology, which coexists to about 40%, with the original one. The new framework consists of a sequence of a novel zeolitic cage (described as a 20-hedron formed by fourteen 6mR and six 4mR) and two consecutive cancrinite cages along [0001]. This topology, which is reported in the database of the hypothetical zeolite structures as 166_2_293, belongs to the ABC-6 family and can be described by the following sequence of 6-rings: ABCBCACAB, to be compared with that of levyne AABCCABBC. In the new topology the extraframework cations are distributed over 3 new sites: one at the center of the 6mR a5 [0001] shared by the two cancrinite cages, one near the center of the 6mR a5 [0001] at the base of the new cage, and a last one in a 6mR window of the new cage. The 8mR bidimensional channel system originally present in levyne is therefore absent in the new topology and hence molecular diffusion is likely to be partially hindered in the dehydrated form. The phase transition is not completely reversible, at least in the short term, as only partial rehydration was demonstrated

Toward molecular wires confined in zeolite channels for an effective transport of electronic excitation energy.

Sunlight is the fundamental energy source sustaining life on Earth. Green plants are provided of very sophisticated and highly efficient tools to exploit light, they are able to harvest sunlight and to transport electronic excitation energy by means of a particular “antenna system” to reaction centres (natural photosynthesis). The antenna consists of regular arrangements of chlorophyll molecules held at fixed positions by means of proteins. Light absorbed by any of these molecules is transported - by radiationless energy transfer (FRET) - to reaction centres, providing the energy necessary for the chemical processes to be initiated. A green leaf consists of millions of such well-organized antenna devices. A long-standing challenge has been the development of an artificial system able to mimic the photosynthetic system. Artificial antenna systems can be realized once several organized chromophores are able to absorb the incident light and to channel the excitation energy to a common acceptor component1-3. Artificial antenna can be built by incorporating dyes into the one-dimensional channels of zeolite L (ZL). ZL crystals feature strictly parallel nano sized channels arranged in hexagonal symmetry. These channels can be filled with high concentration of suitable guests. The geometric constraints imposed by the host structure allow achieving supramolecular organization of photoactive guests1. It has been shown2,that the properties of the dye-ZL systems depend on the molecular packing inside the channels, controlling the intermolecular and the dyes/framework interactions In this work we presents a study on the optical properties of a two –dyes antenna system in which fluorenone molecules (donor molecule) and thionine(acceptor molecule) are organized in Zeolite L porosities. To interpret the optical properties of the hybrids a detailed structural study at atomistic level was mandatory. Due to the impossibility of studying from the structural point of view a two –dyes systems, two “one-dye” hybrids (ZL/fluorenone and ZL/thionine) were firstly synthesized and characterized to investigate the intermolecular and the dyes/framework interactions4. The results of thermogravimetric, IR, and X-ray structural refinements carried out for the one-dye system ZL/FL established that 1.5 molecules per unit cell is the maximum FL loading , in contrast with the data reported previously in literature5 and that the FL carbonyl group strong interact with a K+ of the ZL. The FL distribution at maximum loading can be consider as a self-assembly of planar dye molecules into a noncovalent nanoladder. FL molecules organized in such a single, continuous nanostructure of dye molecules did not exhibit significant electronic interactions. Indeed, both absorption (recorded in the diffuse reflectance mode) and photoemission electronic spectra of ZL/FL systems with different FL loading scaled almost linearly in intensity with the amount dye hosted in the unit cell (ranging from 0.5 to 1.5), without significant changes of the spectral profiles. Noticeably, the combination and steady state and time resolved photoluminescence data indicated that even at the maximum loading ca. 90% of FL molecules are photoluminescent, with significant increase in the average quantum yield with respect to FL molecules in solution. Such a finding clearly indicates that excited states coupling (Davydov splitting) is not contributing to the optical properties of the material. The structural study of the ZL/TH system revealed that the maximum possible loading of TH is equal to 0.3 molecules per unit cell in agreement with the TGA and literature data6. Short distances between the carbon, sulfur and nitrogen atoms and two water molecule sites , in turn at bond distance from the oxygen atoms of the main channel, suggested a water-mediated Th-ZL interactions7. Moreover, IR spectroscopy provided evidence of the interaction of the aromatic rings with the environment. This likely resulted in an increase of the rate of non-radiative decay of Th molecules in the electronic excited state, because only ca. 5% of Th molecules hosted in the ZL channel appeared photoluminescent. The occurrence of energy transfer from excited FL molecules forming the noncovalent nanoladder in the ZL channels and Th, in the ground state, deposited on the external surface of ZL particles are currently under investigation. In conclusion, we have here presented a study on the physico-chemical properties of dense molecular wires encapsulated in the one-dimensional pores arrays of Zeolite L. Concerning the optical properties of our composites, no evidence of Davydov splitting emerged from our study, indicating that one of the main competitors of the FRET mechanism is not operative notwithstanding the close packed arrangement of FL. We believe that this feature is of overwhelming relevance in view of application of such a system in artificial antenna systems

Quantifying garnet-melt trace element partitioning using lattice-strain theory: New crystal-chemical and thermodynamic constraints

Many geochemical models of major igneous differentiation events on the Earth, the Moon, and Mars invoke the presence of garnet or its high-pressure majoritic equivalent as a residual phase, based on its ability to fractionate critical trace element pairs (Lu/Hf, U/Th, heavy REE/light REE). As a result, quantitative descriptions of mid-ocean ridge and hot spot magmatism, and lunar, martian, and terrestrial magma oceans require knowledge of garnet-melt partition coefficients over a wide range of conditions. In this contribution, we present new crystal-chemical and thermodynamic constraints on the partitioning of rare earth elements (REE), Y and Sc between garnet and anhydrous silicate melt as a function of pressure (P), temperature (T), and composition (X). Our approach is based on the interpretation of experimentally determined values of partition coefficients D using lattice-strain theory. In this and a companion paper (Draper and van Westrenen this issue) we derive new predictive equations for the ideal ionic radius of the dodecahedral garnet X-site,

Molecular wires confined in zeolite L channels for an effective transport of electronic excitation energy: a synchrotron structural study.

Sunlight is the fundamental energy source sustaining life on Earth. Green plants are provided of very sophisticated and highly efficient tools to exploit light, they are able to harvest sunlight and to transport electronic excitation energy by means of a particular \u201cantenna system\u201d to reaction centers (natural photosynthesis).The development of an artificial system able to mimic the natural phenomenon has been a long-standing challenge. Artificial antenna systems can be realized once several organized chromophores are able to absorb the incident light and to channel the excitation energy to a common acceptor component [1-3]. The optical properties of the systems depend on the molecular packing inside the channels. Artificial antenna can be built by incorporating suitable guests into the one-dimensional channels of zeolite L (ZL). In this work we present a detailed structural study of two hybrid systems in which dyes (fluorenone and thionine) are encapsulated in zeolite L channels. These two molecules were chosen since it has been demonstrated that a \u201ctwo \u2013dyes antenna system\u201d - in which fluorenone (FL) (donor molecule) and thionine (Th) (acceptor molecule) are organized in Zeolite L porosities - shows remarkable optical properties. Due to the impossibility of studying, from the structural point of view a \u201ctwo \u2013dyes systems\u201d, two \u201cone-dye\u201d hybrids (ZL/fluorenone and ZL/thionine) were firstly synthesized and characterized [4]. The results of thermogravimetric, IR, and X-ray structural refinements carried out for the one-dye ZL/FL and ZL/Th systems established that 1.5 molecules of FL and 0.3 molecules of Th per unit cell is the maximum loading, respectively. The FL carbonyl group strong interacts with a K+ of the ZL. On the other hand, short distances between the carbon, sulfur and nitrogen atoms of Th and two water molecule sites, in turn at bond distance from the oxygen atoms of the main channel, suggested a water-mediated Th-ZL interactions. The energy transfer from excited FL molecules, forming the non-covalent nano-ladder in the ZL channel, and Th, deposited on the external surface of ZL particles, is currently under investigation. In conclusion concerning the optical properties of our composites, no evidence of Davydov splitting emerged from our study, indicating that one of the main competitors of the FRET mechanism is not operative notwithstanding the close packed arrangement of FL. We believe that this feature is of overwhelming relevance in view of application of such a system in artificial antenna devices. The authors acknowledge the Italian Ministry of Education, MIUR-Project: \u201cFuturo in Ricerca 2012 - ImPACT- RBFR12CLQD\u201d