Aluminophosphate AlPO Research Articles

Structural study of a novel layered aluminophosphate AlPO-NS having 10-&10-rings micropores by 3D-ED, powder XRD, and solid-state NMR analyses

A crystal structure of a novel aluminophosphate AlPO-NS, which has a crystal morphology of stacked hexagonal plate crystallites (30–50 nm in thickness), was determined utilizing a combination of 3D-ED, powder X-ray diffraction, and solid-state NMR experiments. We previously reported that AlPO-NS could be obtained from a synthetic solution for a typical aluminophosphate AlPO4-5 (Al2O3 : P2O3 : triethylamine : H2O = 1.0 : 1.0 : 3.0 : 250) via AlPO4-5 by prolonged hydrothermal reaction time (T. Kodaira et al. Microporous and Mesoporous Materials 162, 32–35 (2012).). The 3D-ED/microED analysis successfully revealed that AlPO-NS consists of two layers in a unit cell of a hexagonal system. A space group and lattice constants were P6322, and a = 0.941565(12) nm, c = 5.22254(8) nm. A 2D 10-&10-rings micropore structure is incorporated in the layered framework consisting of AlO4, AlO6, and PO4 polyhedra. The structure of AlPO-NS was changed into a disordered structure derived from stacking faults by the calcination above 573 K under the atmosphere. This structural change is due to shrinkage of the interlayer space and (partially) bridging adjacent aluminophosphate layers by dehydration-condensation of facing –OH groups. The calcined AlPO-NS showed nitrogen adsorption ability with a nearly type-I adsorption isotherm. A specific surface area (SBET) and micropore volume (Vmicro) were 300 m2 g−1 and 0.11 mL g−1, respectively. As-synthesized AlPO-NS contained H+ ions for charge compensation and exhibited ion exchange abilities for Na+ and K+ ions when immersed in NaCl and KCl aqueous solutions, respectively. From the above, it was found that AlPO-NS and its calcined form have micropores and physicochemical properties similar to zeolites.

Water adsorption behavior of Mg and Fe substituted microporous AlPO4-5

Isomorphic substitution of zeolite and zeotype materials plays a dominant role in tuning the performance of the materials in adsorption and catalysis. Here, aluminophosphate AlPO4-5 crystals (AFI-type) with variable content of incorporated iron or magnesium were hydrothermally synthesized, characterized, and tested for water adsorption. The metal incorporation altered the growth direction and thus morphology of the resulting crystals, while the Al/P ratio decreased below unity with increasing Fe/Al2O3 or Mg/Al2O3, confirming selective substitution of aluminum. Moreover, the unit cell experienced shrinkage when Fe substituted Al, whereas the MgAPO-5 lattice refinement results revealed minor variation in the lattice parameters. Water vapor adsorption studies revealed that the materials exhibit non-typical, type-V adsorption behavior with initial low uptake, indicating hydrophobicity, followed by a steep capacity increase indicating capillary-like adsorption at higher relative pressures. Metal substitution could tune the behavior, i.e. by increasing hydrophilicity at the lower range of relative pressures, with the onset of the inflection point being shifted to lower P/P0 values with increasing metal content. An Fe-based AlPO4-5 yielded the highest absorption capacity among all adsorbents tested (13 mmol/g at 43 °C). Fowler-Guggenheim calculations showed that the interaction energy (ω) between the adsorbed water molecules was positive for both MgAPO-5 and FeAPO-5 indicating attractive intermolecular interactions, yet a decrease of ω with increasing Me/Al2O3 ratio in the synthesis mixture revealed suppression of intermolecular interactions with metal loading. The reported results and the tailoring of water adsorption behavior by metal substitution can be promising for water sorption/separation applications such as atmospheric water harvesting.

Metal substitution effects of aluminophosphate AlPO4-5 as solid acid catalyst for esterification of acetic acid with ethanol

Metal substitution in aluminophosphates is known to induce unique structural and surface characteristics that can tune catalytic performance. Si, Co, Fe and Mg substituted AlPO4-5 (MeAPO-5) catalysts were hydrothermally prepared, characterized, and evaluated for ethanol - acetic acid esterification. Textural evaluation revealed that the Co and Si analogues possessed an order of magnitude higher mesopore volume compared to the rest of the studied materials. Divalent metal ions (i.e. Co, Fe, and Mg) substituted preferentially Al ions via the SM1 mechanism, as confirmed by the P/Al being greater than one, while Si ions substituted P ions (SM2) initially, followed by substitution of pairs of Al-P ions (SM3) at higher Si content. The esterification catalytic activity was found to follow the order SAPO-5 > > CoAPO-5 > MgAPO-5 ≈ FeAPO-5. The superior performance of SAPO-5 is ascribed to the higher concentration of Brønsted acid sites and faster mass transfer rates due to the relatively small crystal size and larger fraction of mesopores. Notably, the SAPO-5 with the optimal Si content demonstrated comparable stability against deactivation within the range of reaction conditions studied and sustained catalytic activity at prolonged reaction durations when compared to commercial Zeolite β, despite the significantly higher surface area, pore volume and density of acid sites of the latter, primarily attributed to less strong adsorption of the reaction products. The reported parametric results for various metal substitutions shed light towards optimizing aluminophosphate catalysts for esterification applications.

Key Stages in the Formation of AlPO4-11 via the Crystallization of a Boehmite-Based Aluminophosphate Gel

The staged crystallization of aluminophosphate AlPO4-11 from a commercially available aluminum source based on boehmite is studied for the first time by means of X-ray diffraction, 27Al and 31P magic-angle spinning nuclear magnetic resonance, low-temperature nitrogen adsorption–desorption, and scanning election microscopy. It is shown that the synthesis of AlPO4-11 proceeds via the formation of an intermediate phase based on crystalline aluminophosphate with a layered structure. It is found that AlPO4-11 with a high degree of crystallinity and phase purity forms in 6–24 h at 200°C. Lengthening the time of crystallization at 200°C to more than 48 h results in the transformation of AlPO4-11 into nonporous cristobalite. The results can be used to develop means for directional control of the phase purity and degree of crystallinity of commercially important silicoaluminophosphate molecular sieves SAPO-11 with desired properties. These can be used as a base for the synthesis of promising domestic catalysts for the commercial hydroisomerization of higher n-paraffins.

Selective Crystallization of Aluminophosphate Molecular Sieves with an AEL Structure

The effect of the temperature and exposure time of the starting aluminophosphate gels on their chemical and phase composition was studied. When the source of aluminum is its hydrated oxide (boehmite), gels with different contents of ammonium phosphate, undissolved boehmite, and amorphous aluminophosphate can be formed. The formation of a gel with dominant amorphous aluminophosphate allows selective crystallization of AlPO4-11 of high phase purity and ~100% crystallinity. The developed procedure for the preparation of highly dispersed aluminophosphate AlPO4-11 molecular sieves with these properties allows a transition to crystallization of silicoaluminophosphates SAPO-11—promising domestic catalysts for industrial hydroisomerization of n-paraffins in the production of Arctic diesel fuels and group III oils and isomerization of butenes.

Key Stages of the Formation of AlPO4-11 via Crystallization of Aluminophosphate Gel Prepared with Boehmite

The one-dimensional channel pore system and the moderately strong acid centers inherent in aluminophosphate (AlPO4-11) and silicoaluminophosphate (SAPO-11) molecular sieves make them promising catalyst for hydroisomerization of higher n-paraffins. However, the mechanism of crystallization of these materials is not well understood as yet. XRD,27Al and31P MAS NMR, lowtemperature adsorption-desorption of nitrogen, and SEM techniques were used for the first time for studying the stage crystallization of aluminophosphate AlPO4-11 for commercial boehmite based aluminium source. AlPO4-11 was shown to form via an intermediate phase based on layered crystalline aluminophosphate. It was established that highly crystalline and phase-pure AlPO4-11 was formed at 200 °C during 6 to 24 hours. When the crystallization at 200 °C lasted for more than two days, AlPO4-11 turned into non-porous cristobalite. The results obtained will be used for developing methods for deliberate control of the phase composition and crystallinity of industrially important silicoaluminophosphate sieves SAPO-11 with required properties to develop promising catalysts based thereon for large-scale processes of hydroisomerization of n-paraffins.

Synthesis and Characterization of Nanocrystalline Aluminophosphate AlPO4-5 Molecular Sieve

Nanocrystalline aluminophosphate AlPO4-5 molecular sieves were synthesized by hydrothermal method (HTS). Synthesis parameters like time and temperature of crystallization were investigated. Type of template (R) and ratio of R/P2O5 were studied also. Characterization of the synthesized AlPO4-5 were done by powder X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), Fourier transform infrared (FTIR), differential scanning calorimetry-thermogravimetry analysis (DSC-TGA), and N2 adsorption-desorption BET analysis. XRD patterns results showed excellent crystallinity for two types of templates, di-n-propylamine (DPA) and tetrapropyl ammonium hydroxide (TPAOH) for alumminophosphate five (AFI) structure. Nano-level for particle size of 66 nm was revealed by AFM test. Good thermal stability was obtained in DSC-TGA results. Best time and temperature of crystallization of 24h and 190 O C were got. Optimum R/P2O5 for two kind of template was established.

Dehydration mechanism of AlPO4-5: A high-resolution synchrotron X-ray powder diffraction study

We present the results of a study on the thermal stability and dehydration dynamics of the porous aluminophosphate AlPO4-5, from room temperature to 850 °C, carried out by in situ synchrotron X-ray powder diffraction experiments. No phase transitions were observed in the investigated T range. Due to the very low interactions among framework and water molecules, dehydration is already complete at 152 °C. It occurs in two main T ranges, one between 60 and 80 °C and the second one between 90 and 120 °C. During these two stages, the cell volume tends to increase to facilitate the water release. Overall, across the full explored T range, the cell volume increase is only 0.84%, indicating that AlPO4-5 is one of the most rigid zeolite frameworks studied to date. Specifically, after complete dehydration at 200 °C, AlPO4-5 undergoes a negative thermal expansion as a consequence of the decrease in both a and c cell parameters. The expansion coefficients for V, a and c cell parameters, in the 152–850 °C range, are αV = −7.12 (10−6/K), αa = −2.5 (10−6/K), αc = −2.2 (10−6/K), respectively.

The selective adsorption of tellurium in the aluminosilicate regions of AFI- and MOR-type microporous crystals.

Attempts have been made to load tellurium (Te) atoms into the one-dimensional nano-channels of microporous crystals of aluminophosphate AlPO4-5 and of aluminosilicate mordenites of the Na(+) form (Na-MOR) and the H(+)-form (H-MOR) at 673 K. The density of the atoms adsorbed was in the sequence 0 ∼ AlPO4-5 ≪ H-MOR < Na-MOR. AlPO4-5 provides a shallow potential of periodical charge fluctuation for Te atoms, from the alternate ordering of Al and P atoms through O atoms. Mordenite offers a sufficiently strong potential for Te adsorption, but the magnitude varies with the type of cation. Dipoles between framework AlO2(-) anion sites and their Na(+) counter-ions in Na-MOR provide a stronger potential than the Brønsted acid points in H-MOR. The adsorption of Te atoms in the silico-aluminophosphate SAPO-5 was between that of AlPO4-5 and H-MOR, leading us to suspect that Te atoms are selectively adsorbed in the aluminosilicate regions accompanying the Brønsted acid points distributed in the major aluminophosphate network. The aluminosilicate regions in SAPO-5 are below 500 nm in size and are distributed throughout a single crystal.

Architecture of the Ti(IV) Sites in TiAlPO-5 Determined Using Ti K-Edge X-ray Absorption and X-ray Emission Spectroscopies

X-ray absorption and emission spectroscopies, supported by quantum mechanical calculations, were used to determine the architecture of Ti(IV) sites in Ti aluminophosphate AlPO4-5. The chemical sensitivity of the Kβ2,5 X-ray emission lines of Ti was exploited to monitor its local environment, proving that it mainly substitutes P in the framework, with a not negligible fraction substituting Al. Local structure of the substituted sites was found to be considerably deformed with respect to the AlPO4-5 original framework.

Multinuclear Solid-State NMR Studies on the Formation Mechanism of Aluminophosphate Molecular Sieves in Ionic Liquids

In the present work, multinuclear solid-state NMR techniques together with power X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to monitor the crystallization process of aluminophosphate AlPO4-11 molecular sieves in 1-ethyl-3-methylimidazolium bromide ([emim]Br) ionic liquids (ILs). The local environments of the selected solid samples were probed by one-dimensional 27Al, 31P, and 19F MAS NMR experiments, and more information was obtained from two-dimensional 27Al→31P heteronuclear correlation (HETCOR) and 27Al triple-quantum MAS (3Q MAS) experiments. It is found that a large amount of amorphous aluminophosphates was formed with the F–Aloct–O–Ppar and Altet–O–Ppar structures in the initial stage of aging. With increasing crystallization time, the partially condensed framework phosphorus species disappeared gradually and became fully condensed. Meanwhile, the octahedral Al was transformed into the pentahedral and tetrahedral Al species with the structures of F–Alpenta–O–Pful and Altet–O–Pful in the AlPO4-11 frameworks. During the crystallization process, [emim] cations acting as the structure-directing agents were occluded into the channels, and F– anions were connected with pentahedral Al in the final AlPO4–11 phase. All of these findings can allow proposing a possible formation mechanism for the synthesis of AlPO4-11 in ionic liquids.

Ionothermal synthesis process for aluminophosphate molecular sieves in the mixed water/ionic liquid system

The synthesis process of aluminophosphate AlPO(4)-11 molecular sieve in the mixed water/1-butyl- 3-methylimidazolium bromide ([bmim]Br) ionic liquid was investigated by XRD, multinuclear solid-state NMR, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). It was observed that a tablet phase, named SIZ-2, was formed at the early stage of crystallization. During crystallization metastable SIZ-2 with an incompletely condensed framework phosphorus disappeared gradually, and the phosphorous species became fully condensed through hydroxyl reaction with tetrahedral aluminum to form thermodynamically stable AlPO(4)-11 in the final product. It was found that [bmim]Br, acting as the structure-directing agent, was occluded into the AlPO(4)-11 channel.

Molecular engineering of microporous crystals: (IV) Crystallization process of microporous aluminophosphate AlPO 4-11

The products of microporous aluminophosphate AlPO 4-11 crystallized for different periods of time were freeze-dried and characterized by XRD and NMR techniques. Six crystallographically distinct Al- and P-centered large fragments and 34 small fragments of dimer (Al–P), trimer (Al–P–Al and P–Al–P), tetramer (Al–P 3 and P–Al 3), pentamer (Al–P 4 and P–Al 4), and 4- and 6-membered rings were extracted from the framework of AlPO 4-11. Each of the six large fragments contained two completed coordination layers surrounding the centered atom. The shielding tensors of the Al and P atoms of the fragments were calculated using the quantum mechanics density functional theory. The experimentally observed chemical shifts of Al or P from the well-crystallized AlPO 4-11 were assigned to the shielding tensors of the center atoms of the six large fragments and were further used as references in the determination of the chemical shifts of the Al or P atoms in the small fragments. A comparison of the calculated chemical shifts of the Al and P atoms in the small fragments to the experimental data of the products isolated at different crystallization periods suggested that the fragments of dimers, trimers of the form Al–P–Al, tetramers of the form P–Al 3, and pentamers may exist in the crystallization process of AlPO 4-11. On the basis of these observations regarding the putative small fragments, a possible crystallization process of AlPO 4-11 was proposed.

Multiple resonance heteronuclear decoupling under MAS: Dramatic increase of spectral resolution at moderate magnetic field and MAS frequencies

The effects of multiple-resonance heteronuclear decoupling under magic angle spinning (MAS) on the resolution of one-dimensional 19F and 31P and various two-dimensional MAS NMR spectra and on the residual non-refocusable coherence lifetimes in fluorinated aluminophosphate AlPO 4-CJ2, i.e. a compound that contains numerous highly abundant nuclei but no homonuclear spin bath, has been investigated. The design of the four-channel ( 1H, 19F, 27Al, 31P) MAS probe used for this study is first described. 1H and 1H– 27Al double-resonance decouplings allows lengthening the optimized transverse relaxation T 2 opt and increasing the resolution in the 19F and 31P dimensions. Under the application of multi-nuclear decoupling, a two-dimensional 19F– 31P CP-HETCOR correlation spectrum for AlPO 4-CJ2 is recorded with unprecedented high-resolution in the two dimensions. Moreover, because 1H-decoupling increases the 19F T 2 opt , it has been applied during the entire duration of the 2D NMR experiments, allowing the direct use of residual small interactions to generate 19F– 19F and 19F– 27Al 2D NMR correlation spectra in AlPO 4-CJ2.

On stability and performance of highly c-oriented columnar AlPO 4-5 and CoAPO-5 membranes

Continuous films comprised of highly c-oriented aluminophosphate AlPO 4-5 or cobalt-substituted AlPO 4-5 (CoAPO-5) were grown on porous supports and subjected to heat treatment in order to investigate the potential for membrane applications. A study in the early stages of in-plane crystalline intergrowth revealed a potential mechanism for flake-like crystal formation between the original oriented columnar crystals. Variations in metal substitution (AlPO 4-5, CoAPO-5), support (glass, silicon, porous alumina), and calcination method (conventional, rapid thermal processing) were chosen to examine the conditions by which structural integrity was compromised following secondary (or tertiary) growth, resulting in reduced membrane functionality. Through the use of rapid thermal processing, the structure debilitation could be partially avoided. The membrane quality was inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene. By investigating the effect of template removal on the oriented, columnar crystalline structure, useful insight is provided into the potential for the membranes to participate in applications such as molecular separations, catalysis, or host–guest assemblies.

Molecular engineering of microporous crystals: (III) The influence of water content on the crystallization of microporous aluminophosphate AlPO 4-11

The influence of water content on the crystallization of the microporous aluminophosphate AlPO 4-11 was investigated by a combination of in situ UV Raman and ex situ XRD and NMR characterizations. Under high water content conditions (Al 2O 3:H 2O = 1:20–69), an AlPO 4-5 intermediated formed first and later co-existed with AlPO 4-11. In the last stage of crystallization, the crystalline AlPO 4-5 completely disappeared and well-crystallized AlPO 4-11 was obtained. The position of the three signals observed in the 31P MAS NMR spectra of the isolated solid samples did not change during the hydrothermal treatment, suggesting that the fragments containing the P site in the junction of 6- and 4-membered rings of both AlPO 4-5 and AlPO 4-11 formed first and that the environments of the P sites were very similar to those in the final structure. A significant increase of Al concentration in liquid media was observed before the appearance of XRD detectable AlPO 4-11. Under low water content conditions (Al 2O 3:H 2O = 1:15), the AlPO 4-11 was directly crystallized from the initial mixture. In situ Raman spectra showed that the 10-membered rings were complete by the time the transformation of octahedral Al to tetrahedral Al was finished and that the conformation of the protonated di-( i-propyl)amine changed little during the crystallization. The present study showed that the composition of the liquid phase is critical to the formation of a specific structure.

Decision Trees Combined with Feature Selection for the Rational Synthesis of Aluminophosphate AlPO&lt;sub&gt;4&lt;/sub&gt;-5

Decision Trees Combined with Feature Selection for the Rational Synthesis of Aluminophosphate AlPO&lt;sub&gt;4&lt;/sub&gt;-5

Prediction of Microporous Aluminophosphate AlPO4 -5 Based on Resampling Using Partial Least Squares and Logistic Discrimination.

In this paper, Partial Least Squares (PLS) regression and Logistic Discrimination (LD) are employed to predict the formation of microporous aluminophosphate AlPO4 -5 based on the database of AlPO synthesis, which aims to provide a useful guidance to the rational synthesis of microporous materials as well as other inorganic crystalline materials. To deal with the problem of class imbalance, four guided resampling methods considering not only the between-class imbalance but also the within-class imbalance are proposed. Experimental results indicate that the presented methods are competent for predicting the formation of microporous aluminophosphate AlPO4 -5. Specially, compared with some existing resampling methods, our proposed resampling methods exhibit much better predictive results.

1D to 3D NMR study of microporous alumino‐phosphate AlPO4‐40

From one- to two- and three-dimensional MAS NMR solid-state experiments involving (31)P and (27)Al, we show that the structure of microporous alumino-phosphate AlPO(4)-40 contains at least four times more sites than expected, and we attribute two types of Al(IV) sites. The newly described (27)Al-(31)P MQ-HMQC opens new possibilities of describing details of three-dimensional bounded networks.

Heteronuclear dipolar recoupling of half-integer quadrupole nuclei under fast magic angle spinning

An experimental method for the heteronuclear dipolar recoupling of half-integer quadrupole nuclei is proposed. The idea is to manipulate the central transition based on the recoupling technique of spin-polarization-inversion rotary resonance. This method allows the extraction of structural parameters under fast magic-angle spinning. Its validity has been examined by the average Hamiltonian theory and numerical simulations. The initial rotational-echo dephasing arising from the dipolar evolution can be approximated by a parabolic function, from which the heteronuclear van Vleck second moment can be estimated. A factor, estimated from two-spin simulations, is required to account for the effects of the quadrupolar coupling and is rather independent of the geometry and the orders of the spin systems. Our method can facilitate the structural characterization of materials containing half-integer quadrupole nuclei under high-resolution condition. Experimental verification has been carried out on two aluminophosphate systems, namely, AlPO 4-5 and AlPO 4-11.