Porous Aluminophosphates Research Articles

Direct Single Crystal to Amorphous Transformation and Memory Effect in AlPO4-17.

Pressure induced amorphization provides a distinct route to prepare novel amorphous materials. Single crystals of the porous aluminophosphate AlPO4-17 directly transform to an amorphous state beginning at 0.6 GPa, without fragmentation into polycrystalline material. Apart from a reduction in dimensions, the amorphous material retains the form of the initial single crystal. Remnant crystalline domains in the amorphous material also preserve the initial orientation of the single crystal. X-ray diffraction indicates the compression of the structure around the empty pores in the xy plane and such an amorphization mechanism is consistent with a direct structural relationship between the single crystal and amorphous forms. The collapse of the initial pore volume is almost complete at 2.5 GPa. A memory effect is observed in the amorphous form, which strongly expands on decompression. The present process opens the way for the synthesis of topologically ordered amorphous materials approaching "perfect glasses" with improved mechanical properties.

Strongly Modified Mechanical Properties and Phase Transition in AlPO4-17 Due to Insertion of Guest Species at High Pressure.

The porous aluminophosphate AlPO4-17 with a hexagonal erionite structure, exhibiting very strong negative thermal expansion, anomalous compressibility, and pressure-induced amorphization, was studied at high pressure by single-crystal and powder X-ray diffraction in the penetrating pressure transmitting media N2, O2, and Ar. Under pressure, these guest species were confirmed to enter the pores of AlPO4-17, thus completely modifying its behavior. Pressure-induced collapse in the xy plane of AlPO4-17 no longer occurred, and this plane exhibited close to zero area compressibility. Pressure-induced amorphization was also suppressed as the elastic instability in the xy plane was removed. Crystal structure refinements at a pressure of 5.5 GPa indicate that up to 28 guest molecules are inserted per unit cell and that this insertion is responsible for the reduced compressibility observed at high pressure. A phase transition to a new hexagonal structure with cell doubling along the a direction was observed above 4.4 GPa in fluid O2.

Tuning Negative Thermal Expansion in AlPO4-17 by Insertion of Guest Molecules.

The very strong negative thermal expansion in the porous aluminophosphate AlPO4-17 with a hexagonal erionite structure was tuned by the insertion of oxygen molecules at high pressure. The structure of the oxygen-filled material was determined in situ at high pressure by synchrotron, single-crystal X-ray diffraction. The thermal expansion of this material was measured precisely at 0.38 GPa by synchrotron X-ray powder diffraction. Whereas the overall volume thermal expansion only exhibits a small change with respect to empty AlPO4-17 at ambient pressure, the expansion along the a direction decreases almost to zero and the expansion along c increases by a factor of 7. Such highly anisotropic thermal expansion properties are of great interest for mechanical and optical applications as in two directions the dimensions of the material are extremely stable, whereas a very strong linear negative thermal expansion of -2.2 × 10-5 K-1 is observed in the perpendicular direction. Guest insertion is thus a very powerful tool for tuning the thermal expansion properties of porous materials.

Ultralow-temperature-driven water-based sorption refrigeration enabled by low-cost zeolite-like porous aluminophosphate

Thermally driven water-based sorption refrigeration is considered a promising strategy to realize near-zero-carbon cooling applications by addressing the urgent global climate challenge caused by conventional chlorofluorocarbon (CFC) refrigerants. However, developing cost-effective and high-performance water-sorption porous materials driven by low-temperature thermal energy is still a significant challenge. Here, we propose a zeolite-like aluminophosphate with SFO topology (EMM-8) for water-sorption-driven refrigeration. The EMM-8 is characterized by 12-membered ring channels with large accessible pore volume and exhibits high water uptake of 0.28 g·g−1 at P/P0 = 0.2, low-temperature regeneration of 65 °C, fast adsorption kinetics, remarkable hydrothermal stability, and scalable fabrication. Importantly, the water-sorption-based chiller with EMM-8 shows the potential of achieving a record coefficient of performance (COP) of 0.85 at an ultralow-driven temperature of 63 °C. The working performance makes EMM-8 a practical alternative to realize high-efficient ultra-low-temperature-driven refrigeration.

Exploring the origins of crystallisation kinetics in hierarchical materials using in situ X-ray diffraction and pair distribution function analysis.

The discovery of novel catalytic materials is predicated on understanding contemporary synthetic processes. With this fundamental knowledge in place it becomes possible to modify the final material with subtle changes to the synthesis process. In this vein, hierarchical materials, formed by the addition of a mesoporogen within the hydrothermal synthesis, have attracted a significant amount of attention due to their catalytic benefits over analogous microporous species. In this work we monitor the hydrothermal synthesis in situ of a hierarchical and a microporous aluminophosphate, for the first time, combining total scattering and pairwise distribution function data. In doing so we observe the local formation of the species, and the longer range crystallisation processes concurrently.

Highly porous aluminophosphates with unique three dimensional open framework structures from mild hydrothermal syntheses

Three novel highly porous aluminophosphates were synthesized through mild hydrothermal methods. Interestingly, among them, α-NaAlPO4(OH) is polar and exhibits moderate nonlinear optical properties with a short cutoff edge.

First-Principles Study of AlPO₄-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules.

Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two “types” of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type small-pore aluminophosphate AlPO4-H3 contains both types of H2O molecules. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO4-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO4-C, leading to the identification of a few “fingerprint” modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO4-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.

Explaining water adsorption in one-dimensional channels in AlPO4-5 on molecular scale

Abstract The adsorption of water in one-dimensional channels in porous aluminophosphate material AlPO4-5 has been studied by a combination of gravimetric analysis techniques, neutron and X-ray diffraction and neutron spectroscopy. Molecular structure of AlPO4-5 consists of 12-membered rings of alternating, corner-sharing AlO4 and PO4 tetrahedra connected by oxygen bridges into sheets in the (a, b) plane. The sheets are connected by oxygen bridges along the c crystal axis and form one-dimensional channels of which the largest, formed by the 12-membered rings, have a van der Waals diameter of about 8.3 A. Gradually increasing the amount of adsorbed water we could follow the evolution of the confined water mobility in a systematic way and identify the molecular mechanism of water adsorption. We focused particularly on the range of low and medium relative pressures up to p/p0 = 0.32, where a change from a hydrophobic behavior to a steep, capillary condensation like water intake has been observed. At the initial adsorption stages water occupies positions close to the pore walls causing the contraction of channels in the (a, b) plane and the prolongation of the channels along c axis in AlPO4-5. With the progressing intake water molecules form chains along the main channels. The cooperative interactions between water molecules lead to the onset of phonon-like cooperative modes and, surprisingly, to the increase of diffusive-like motion, which slow down only in the final adsorption stages when AlPO4-5 channels are completely filled.

Porous aluminophosphates as adsorbents for the separation of CO2/CH4and CH4/N2mixtures – a Monte Carlo simulation study

Force-field based Monte Carlo simulations are employed to investigate the adsorption of methane-containing mixtures in 53 structurally distinct aluminophosphate frameworks.

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.

Interaction of water with (silico)aluminophosphate zeotypes: a comparative investigation using dispersion-corrected DFT

Porous aluminophosphates (AlPOs) and silicoaluminophosphates (SAPOs) with zeolite-like structures have received considerable attention as potential adsorbents for heat transformation applications using water adsorption/desorption cycles. Since a detailed experimental characterisation of the water adsorption properties has only been performed for some of these materials, such as AlPO-18 (AEI topology) and SAPO-34 (CHA topology), more systematic insights regarding the influence of the pore topology and (for SAPOs) the arrangement of the framework protons on the affinity towards water are lacking. To study the relationships between structure and properties in more detail, the interaction of water with six structurally different AlPOs (with AEI, AFX, CHA, ERI, GIS, RHO topologies) and their SAPO analogues was investigated using dispersion-corrected density-functional theory (DFT-D) calculations. Different possible locations of silicon atoms and charge-balancing protons were considered for the SAPO systems. The calculations for SAPOs at low water loadings (one H2O molecule per framework proton) revealed that the interaction energies exhibit a considerable variation, ranging from −75 to −100 kJ mol−1 (per water molecule). The differences in interaction energy were rationalised with the different structural environment of the framework protons at which the water molecules are adsorbed. At high water uptakes (near saturation), interaction energies in the range of −65 kJ mol−1 were obtained for all AlPOs, and there was no evidence for a marked influence of pore size and/or topology on the interaction strength. The interaction of water with SAPOs was found to be approximately 5 kJ mol−1 stronger than for AlPOs due to an increased contribution of electrostatic interactions. An analysis of the structural changes upon water adsorption revealed striking differences between the distinct topologies, with the materials with GIS and RHO topologies being distorted much more drastically than the systems based on double six-ring (d6r) units. Moreover, the direct coordination of water molecules to framework aluminium atoms occurs more frequently in these materials, an observation that points towards a reduced structural stability upon hydration.

Synthesis, Characterization and Catalytic Applications of Hierarchically Porous Aluminophosphate Molecular Sieves

Synthesis, Characterization and Catalytic Applications of Hierarchically Porous Aluminophosphate Molecular Sieves

“Solvent-free” synthesis of thermally stable and hierarchically porous aluminophosphates (SF-APOs) and heteroatom-substituted aluminophosphates (SF-MAPOs)

Hierarchically porous aluminophosphates (SF-APOs) and metal substituted aluminophosphates (SF-MAPOs, M = Co, Fe, Cr) have been synthesized via simple grinding and heating in the absence of solvent. Characterization results show that these mesoporous aluminophosphates have a hierarchically microporous/mesoporous structure. In addition, metal atoms can be efficiently incorporated into the walls of mesoporous aluminophosphates, and the SF-CoAPO sample shows high catalytic activity in cyclohexene oxidation compared with microporous samples. Special features of the “solvent-free” synthesis route, such as increasing product yield, saving energy, elimination of pollution, and convenience for incorporation of heterogeneous atoms, ensure its great potential in the synthesis of porous materials.

Formation of Porous Aluminophosphate Frameworks Monitored by Hyperpolarized 129Xe NMR Spectroscopy

The formation of two aluminophosphate frameworks, AlPO4-5 and AlPO4-18, has been monitored using hyperpolarized 129Xe NMR as a probe. The reaction progress from an amorphous phase to AlPO4-5 and its subsequent conversion to AlPO4-18 is observed for xenon adsorbed in samples that have been reacted for varying lengths of time. The extreme sensitivity of 129Xe chemical shifts to local environments of the xenon leads to separate NMR peaks for xenon adsorbed in the two different aluminophosphate frameworks present in a single reaction mixture. For xenon adsorbed in AlPO4-5, an anisotropic 129Xe NMR line shape at δiso ≈ 63 ppm is observed, whereas for xenon in AlPO4-18, a peak with a small anisotropy at δiso ≈ 74 ppm is observed. Grand canonical Monte Carlo simulations provide a theoretical description of xenon adsorbed in the two aluminophosphate frameworks, and the resulting simulated 129Xe NMR line shapes are in good agreement with experimental data. Two-dimensional exchange NMR spectroscopy was used to examine the exchange of xenon between AlPO4-5, AlPO4-18, and bulk xenon gas. The results indicate that the domains of AlPO4-5 are in intimate contact with those of AlPO4-18, facilitating a higher intercrystallite exchange than with the bulk xenon gas.

Porous Aluminophosphates: From Molecular Sieves to Designed Acids Catalysts

Porous Aluminophosphates: From Molecular Sieves to Designed Acids Catalysts

POROUS ALUMINOPHOSPHATES :From Molecular Sieves to Designed Acid Catalysts

▪ Abstract This review covers the synthesis, characterization, and physico-chemical properties of microporous and mesoporous aluminophosphates and silicoaluminophosphates molecular sieves. Particular emphasis is given to the materials that have found applications as acid catalysts. We consider the evolution of the synthesis procedures from the first discoveries to the current methodologies and give perspectives for new possible synthesis strategies. Emphasis is given to the use of specially prepared precursors/reactants designed for the use as molecular sieves. Experimental (especially MAS-NMR and FTIR spectroscopy) and theoretical approaches to the description of the Si insertion into the ALPO framework and to the acidic properties of SAPOs and MeAPSOs materials are discussed.

Structural State and Redox Behavior of Framework Co(II) in CoIST-2: A Novel Cobalt-Substituted Aluminophosphate with AEN Topology

A highly crystalline cobalt-substituted aluminophosphate with an AEN topology, labeled CoIST-2, has been synthesized and characterized by powder XRD, TG/DSC, diffuse reflectance UV−vis spectroscopy, FTIR, EPR spectroscopy, and cyclic voltammetry. Both water and methylamine were shown to play a complementary role as dual template and space-filling agents during the hydrothermal synthesis of this material. The spectroscopic (EPR, UV−vis, and FTIR) and electrochemical characterization of the as-synthesized and calcined CoIST-2 material revealed the presence of two structurally different Co(II) species incorporated in its crystalline framework. The redox behavior and acidity was found to be different for these two Co(II) species. While one of these cobalt species corresponded to Brönsted Co(OH)P acid sites, the other seemed to be associated with the presence of Lewis acid sites (Co□P type species). UV−vis spectra, typical of divalent cobalt in tetrahedral coordination, along with FTIR, demonstrated that only a fraction of the Co(II) ions undergo a reversible oxidative process after calcination in air and that some extraframework CoxOy type species are also generated through oxidation. The presence of divalent Co(II) in a slightly distorted tetrahedral coordination, both in the as-synthesized and calcined phase, was also detected with use of EPR data. The electrochemical oxidation of the two different framework Co(II) species and their further reduction could be evaluated semiquantitatively by cyclic voltammetry. The redox ability of CoIST-2 was also compared with that of two other cobalt-substituted aluminophosphates involving different pore structures, namely CoAPO-40 and CoAPO-37, by using FTIR of adsorbed NO. It was found that the most readily oxidized ions were present in the more dense AEN topology, followed by the more open AFR and FAU structures, thereby emphasizing how the redox properties of transition metal ions in porous aluminophosphates are intimately linked to both the structure type/density of the host lattice and framework positions of the heteroelement.

Tuning the pore size from micro- to meso-porous in thermally stable aluminophosphates

Thermally stable porous aluminophosphates (ICMUV-3) with P/Al molar ratios in the range 0.15 ⩽ P/Al ⩽ 0.75 and showing continuously adjustable pore sizes from 13 to 37 A have been prepared through a surfactant-assisted procedure without changing the surfactant length and/or addition of organic expansors.

A solid-state NMR study of the molecular sieve VPI–5 synthesized in the presence of a CTABr surfactant

Silicon-free and silicon-rich large-pore aluminophospate VPI–5, synthesized with various contents of AlPO–H3 impurity, was studied by Bloch decay (BD) and cross polarization (CP) NMR under magic angle spinning (MAS). The 1 H→ 31 P CP peaks were considerably stronger from AlPO–H3 than from VPI–5. A detailed examination of the CP kinetics and a careful comparison of the CP and BD spectra are prerequisites for the unequivocal interpretation of 1 H→ 31 P CP in porous aluminophosphates.

Solid-state NMR studies of hydrated porous aluminophosphate VPI-5

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolid-state NMR studies of hydrated porous aluminophosphate VPI-5Joao Rocha, Waclaw Kolodziejski, H. He, and Jacek KlinowskiCite this: J. Am. Chem. Soc. 1992, 114, 12, 4884–4888Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/ja00038a064RIGHTS & PERMISSIONSArticle Views178Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts