769 research outputs found
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 Ă…, 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
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 Ă…, 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
on the use of arima models for short term water tank levels forecasting
Abstract
In this paper a statistical study on the time series of water levels measured, during 2014, in the water tank of Cesine, Avellino (Italy), is presented. In particular, the autoregressive integrated moving average (ARIMA) forecasting methodology is applied to model and forecast the daily water levels. This technique combines the autoregression and the moving average approaches, with the possibility to differentiate the data, to make the series stationary. In order to better describe the trend, over time, of the water levels in the reservoir, three ARIMA models are calibrated, validated and compared: ARIMA (2,0,2), ARIMA (3,1,3), ARIMA (6,1,6). After a preliminary statistical characterization of the series, the models' parameters are calibrated on the data related to the first 11 months of 2014, in order to keep the last month of data for validating the results. For each model, a graphical comparison with the observed data is presented, together with the calculation of the summary statistics of the residuals and of some error metrics. The results are discussed and some further possible applications are highlighted in the conclusions
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
Fluorenone dye-Zeolite L hybrid: a novel optical material
A major challenge facing humanity is developing renewable source of energy. Following the biological blueprint of the natural photosynthesis is possible design synthetic systems for converting light into stored energy: the so called artificial antenna systems. The encapsulation of ordered chromophore molecules into one dimensional zeolite channel systems results in host-guest compounds suitable for the development of novel optical materials such as lenses, infrared light-emitting diodes (used in telecommunications) or dye nanostructured materials for optical data storage [1]. X-ray powder diffraction study of zeolite K-L loaded with 0.5, 1, 1.5, 2 fluorenone-dye (FL) molecules per unit cell (ZL/FL hybrid) [2], was carried out to understand the functionality of these host-guest systems from the structural point of view. These data evidenced a significant change of the unit cell parameters due to the embedding of FL into the ZL 12-membered channels. The Rietveld refinements revealed that the maximum loading is 1.5 FL molecules per unit cell. A strong interaction between FL carbonyl group and two extraframework potassium cations is proved by the short bond distances which make this composite very stable
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 Ă…. 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) Ă…3, K0 = 54(3) GPa and V0 = 784(2) Ă…3, 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
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