Aluminophosphate Molecular Sieves Research Articles

Adsorption Properties of Aluminophosphate Molecular Sieves with AEL and AFI Structures According to Gas Chromatography Data

Adsorption Properties of Aluminophosphate Molecular Sieves with AEL and AFI Structures According to Gas Chromatography Data

Unraveling a Stable 16-Ring Aluminophosphate DNL-11 through Three-Dimensional Electron Diffraction for Atmospheric Water Harvesting.

Sorption-based atmospheric water harvesting (AWH) is a promising solution for addressing water scarcity. Developing cost-effective and stable water adsorbents with high water uptake capacity and a low-temperature regeneration requirement is a crucially important procedure. In this Communication, we present a novel and stable aluminophosphate (AlPO) molecular sieve (MS) named DNL-11 with 16-ring channels synthesized by using an affordable and commercialized organic structure directing agent (OSDA), whose crystallographic structure is elucidated by three-dimensional electron diffraction (3D ED). DNL-11 exhibits a significant water uptake capacity (189 mg/g) at a very low vapor pressure (5% relative humidity at 30 °C). In addition, most of the adsorbed water can be effortlessly removed by purging N2 at 25 °C under ambient pressure conditions. This may expand the possibility of AWH under extreme drought conditions.

Ultrafast and continuous synthesis of an aluminophosphate type zeolite in microchannel and the hydrogenation of α-pinene

A highly efficient method was proposed for fast and continuous synthesis of LTA-type aluminophosphate (AlPO4-LTA) molecular sieves. The precursor was first synthesized in batch methods, then the precursor and tetramethyllamine hydroxide were coordinated to direct the synthesis of molecular sieves in a reaction system containing a poly (tetrafluoroethylene) (PTFE) microchannel reactor, which reduced the energy costs associated with mixing and cooling of reactant solutions. The reaction conditions, including molar ratio of reagents, temperature and flow rate, have also been rapidly optimized. The AlPO4-LTA have high crystallinity, high thermal stability, granule size (ca. 150 nm) and large surface area (679 m2/g). In addition, the hydrogenation of α-pinene catalyzed by Ni/AlPO4 nanocomposites was achieved with α-pinene conversion rate of 95.1% and cis-pinane selectivity of 95.9%, the catalyst had high activity during five cycles.

Cuprous oxide-loaded AlPO4-5 for highly efficient iodide ions adsorption in chloride molten salt

Developing high-efficiency adsorbent materials for iodide ions in molten salt systems is of great practical significance in nuclear fuel pyroprocessing. In the present work, a cuprous oxide-loaded AlPO4-5 as Cu2O/AlPO4-5 was successfully prepared by copper ammonium complex self-pyrolysis. The adsorption behaviour of Cu2O/AlPO4-5 for iodide ions from chloride molten salt was investigated by a series of static adsorption experiments. It was found that Cu2O/AlPO4-5 exhibited higher iodide ions adsorption capacity (171.63 mg/g) compared with AlPO4-5 (53.49 mg/g) in LiCl–KCl molten salt at 823K, and the adsorption capacity reached the maximum within 2 h. The significant adsorption properties were further proved to mainly result from nanoscale Cu2O particles, which promoted the adsorption material to exhibit chemisorption behaviour, except for the original physisorption. Cu2O/AlPO4-5 also showed adsorption capacity for other ions when anions or cations coexist in molten salt. Our results suggested that aluminophosphate molecular sieves loaded by Cu2O could be applied as adsorbents for radioactive iodide in the molten salt system.

Enhanced performance of thin-film nanocomposite membranes achieved by hierarchical zeolites for nanofiltration

Nanosized zeolite molecular sieves are increasingly explored for developing high-performance nanocomposite membranes, mainly because of their ordered pore structures and remarkable thermal stability. In this study, hierarchical nanosized aluminophosphate molecular sieves [AlPO-5 (AFI)] were synthesized as functional fillers to construct thin-film nanocomposite (TFN) membranes. Nanosized AlPO-5 was effectively positioned onto porous polysulfone supports via a filtration-assisted method, followed by in situ interfacial polymerization to construct a polyamide layer atop the modified supports. The synthesized nanosized AlPO-5 crystals have both intrinsic micropores and abundant intracrystalline mesopores. SEM and AFM analyses reveal that the introduction of AlPO-5 not only enhanced the surface roughness of TFN membranes with valley-shaped surface but also substantially decreased the thickness of a polyamide layer compared to nodular-shaped TFC membranes. These differences are mainly ascribed to retarded piperazine diffusion and positioned AlPO-5 nanoaggregates. The role of AlPO-5 loading in overall separation performance of TFN membranes was studied. The best-performing TFN membranes showed the highest water permeability of 23.2 L m−2 h−1 bar−1, nearly twice that of unmodified TFC membranes, while maintaining a high salt rejection of 97.5%. The thickened and roughened polyamide layer with reduced transport resistance as well as intrinsic abundant mesopores of AlPO-5 fillers mainly contribute to the enhanced water transport. This study highlights the usage of hierarchical zeolite molecular sieves to fabricate high-permeable polyamide membranes for elevated nanofiltration performance.

The Effects of AlPO-n Additives as Catalytic Support on Pd-Catalytic Hydrogenation of 2-Amylanthraquinone Process

The Pd-catalyzed hydrogenation of anthraquinone to synthesize hydrogen peroxide is an important process in the chemical industry. A Pd catalyst with high dispersion is the key to hydrogenation activity and selectivity. For the first time, this team introduced the AlPO-5 zeolite to SiO2 powder to prepare a finely dispersed Pd catalyst with higher efficiency than the conventional Pd/SiO2 catalyst. Based on previous research, other aluminophosphate molecular sieves (AlPO-n) with different properties from AlPO-5 were introduced to the SiO2 support, and then the synthesized hydrogenation catalysts were characterized by the BET, XRD, H2-TPR, NH3-TPD, H2-TPD, XPS and HRTEM methods and then tested for the hydrogenation of 2-amylanthraquinone in a continuous stirred tank reactor (CSTR). It was demonstrated that the Pd-AlPO-31/SiO2 catalyst exhibits superior H2O2 yield (8.4 g·L−1) and selectivity (96%) among all prepared Pd-AlPO-n/SiO2 and Pd/SiO2 catalysts. The characterization results suggest that the dimensions and structure of AlPO-31 micropore channels are responsible for highly dispersing Pd particles, preventing the accumulation of Pd particles, and intensifying H2 adsorption in its micropore channels, which is significant for the catalytic activity.

Aluminophosphate - Based adsorbents for atmospheric water generation

Freshwater resources are being heavily depleted and not replenished at the same high rate, thus, atmospheric water vapor harvesting has earned growing interest. Development of high-performing desiccant or adsorbent materials offering high sorption capacity and selectivity as well as regeneration capability in atmospheric conditions is crucial to tackle water scarcity. The required properties to generate potent water sorbents include pore accessibility, high specific surface area and porosity to enable high capture capacity and kinetics, and hydrothermal resilience to resist cyclic sorption and desorption. Further, polarity, hydrogen bonding, adhesion ability of water molecules to adsorbent surface, and hydrophilic functional groups can boost water adsorption. A highly promising class of water vapor adsorbents is the aluminophosphate molecular sieves (AlPOs), which are microporous zeotype materials. In this review, AlPO-based adsorbents are discussed for water sorption applications and a link is established between performance of materials and their chemical and morphological properties. Synthesis-properties-performance relationships are elucidated in light of synthesis techniques and adsorption behavior, and prospects to enhance AlPOs' water vapor sorption performance toward large-scale water harvesting applications are highlighted.

Investigations on the intrinsic and template-dependent transformations of AlPO4-11 molecular sieve under high pressure

In this study, aluminophosphate molecular sieve AlPO4-11, with one-dimensional elliptical channels, was investigated under high pressure in non-penetrating silicone oil by X-ray powder diffraction, infrared spectroscopy and theoretical simulation, focusing on its intrinsic and template-modified mechanical behaviors. Two distinct compressible regimes were observed for both the calcined and as-synthesized AlPO4-11 frameworks before pressure-induced amorphization (PIA). The channel cross-section in the calcined AlPO4-11 framework showed an obvious increase in the ellipticity during this process. The framework structure began to lose crystallinity at approximately 2–3 GPa and underwent significant amorphization at 6.6 GPa. PIA was mainly induced via the destruction of the constructed species along the periodic crystallographic planes which are parallel to the channel axis. The bulk moduli showed that this empty framework was rather soft in these regimes. For the as-synthesized AlPO4-11 framework, the mechanical stability of the channels was markedly improved by the template molecules. A different elliptic deformation of the cross-section with a reduced contractility in the minor axis direction was presented. Discontinuous volume evolution occurs at 3–4 GPa and significant amorphization was postponed to 13.7 GPa. The as-synthesized AlPO4-11 was stiffer than calcined AlPO4-11 and showed a soft to hard transformation due to the strengthened host-guest interaction upon compression. Moreover, infrared spectra indirectly confirmed the structural collapses by detecting the vibrational characteristics of the embedded template molecules. The present results provided a comparative and basic knowledge of the intrinsic and extrinsic stability, compressibility, channel deformation and collapse of the AlPO4-11 framework under high pressure. This study emphasized the importance of guest molecules in modifying the mechanical behaviors of zeolites and resisting framework collapse.

Ultrafast synthesis of discrete submicron AlPO4-LTA molecular sieve crystals and their application in molecular sieve membrane

Ultrafast synthesis of nanosized and submicron zeolite materials is challenging but highly desired due to their wide applications. Herein, discrete LTA-type aluminophosphate molecular sieve (AlPO4-LTA) submicron crystals have been synthesized in an open glass beaker under oil bath heating for only 10 min. The influences of the synthesis parameters, including the ratios of tetramethylammonium hydroxide (TMAOH)/Al and HF/Al, and the heating methods were investigated thoroughly. The optimized product exhibits exceptional properties, including good crystallinity, small particle size (ca. 130 nm) and large BET surface areas (867 m2/g). The time-dependent study reveals the formation process of submicron AlPO4-LTA crystals: the primary worm-like amorphous first aggregated into loosely assembled spheres, then the crystallinity of the spheres enhances while keeping the particle size unchanged. Using the submicron AlPO4-LTA crystals as the seed layer, an AlPO4-LTA membrane was synthesized via secondary growth approach. For binary mixtures at 298 K, the separation factors for H2/N2, H2/O2, H2/CO2 and H2/CH4 are 4.8, 6.2, 7.3 and 5.9, respectively, suggesting the good gas separation performance of the membrane.

Progress in Seed-assisted Synthesis of (Silico)Aluminophosphate Molecular Sieves

Progress in Seed-assisted Synthesis of (Silico)Aluminophosphate Molecular Sieves

Insight in the Crystallization Kinetics of AlPO4-11 Molecular Sieve Using Di-Isopropylamine as Template

The hydrothermal synthesis of aluminophosphate molecular sieve type AlPO4-11 was processed from chemicals containing psueudobohemite, 85% phosphoric acid, water, and di-isopropylamine as templating agent. The crystallization of the samples was studied by taking samples in times from 2 to 74 h. The obtained white powder products were characterized by X-ray diffraction patterns (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG) and differential scanning calorimetry (DTG) data and pH measurement of the mother liquor. The pore volume, as determined from TG and DTG curves, was ca. 0.17 cm3g−1. The percent relative crystallinity was determined by XRD and FT-IR methods. The crystallization kinetics evidenced that the hydrothermal synthesis of AlPO4-11 exhibited in its initial phase a behavior of first order reaction with a specific velocity constant of ca. 0.25 h−1, as determined from XRD and FT-IR data. The results obtained by both X-ray diffraction and infrared spectroscopy are comparable, and FT-IR is found to be a rapid method for estimating crystallinity and structure of aluminophosphate.

The Exploration of Dominant Factors for the Hydrogenation of α-Pinene Over Ni–P/APO-11

APO-11 aluminophosphate molecular sieve was prepared by hydrothermal method of aluminum hydroxide with diisopropylamine. Ni–P/APO-11 amorphous alloy catalysts were prepared by chemical reduction method and used for the hydrogenation of α-pinene reaction. The catalysts were characterized by X-Ray photoelectron spectroscopy (XPS), Nitrogen adsorption–desorption isotherms (BET), scanning electron microscope (SEM), transmission electron microscope (TEM) and fourier transform infrared spectrometer (FT-IR).The prepared conditions of the Ni–P/APO-11 catalysts played important roles on the hydrogenation of α-pinene reaction. It was found that the preparation temperature, P/Ni molar ratio and pH value had great influence on the reduction dosage, dispersion and particle sizes of the catalysts, thus affecting the reactivity of the catalysts. The appropriate reaction conditions explored were at 30 °C, n(P/Ni) = 5 and pH = 8, obtaining a 90.65% conversion of α-pinene and 97.87% selectivity to cis-pinane. Under these conditions, the catalysts exhibited better repeatability and stability.

Cover Feature: Structure‐Directing Roles of Organic Molecules in the Formation of Aluminosilicate and Aluminophosphate Molecular Sieves Revealed by 2D 1H DQ‐SQ NMR Spectroscopy (Chem. Eur. J. 6/2021)

Cover Feature: Structure‐Directing Roles of Organic Molecules in the Formation of Aluminosilicate and Aluminophosphate Molecular Sieves Revealed by 2D ¹H DQ‐SQ NMR Spectroscopy (Chem. Eur. J. 6/2021)

Structure-Directing Roles of Organic Molecules in the Formation of Aluminosilicate and Aluminophosphate Molecular Sieves Revealed by 2D 1 H DQ-SQ NMR Spectroscopy.

Understanding of crystallization mechanisms of molecular sieves is driven by the broad range of usefulness and unique properties they possess. It is still difficult to obtain information related to the crystallization mechanism of molecular sieves, partly because the materials are generally prepared under hydrothermal conditions and the whole reaction happens in the "black box" autoclave. In this work, 2D 1 H DQ-SQ NMR results clearly demonstrate that it is not only the electrostatic interactions between organic structure-directing agents (OSDAs) and the framework, but also the correlation among OSDAs playing the dominant structural directing roles during the crystallization process. Our fundamental understanding of the crystallization mechanism of molecular sieves could be of great value to design and synthesize new molecular sieves with desirable structural properties.

Synthesis of Aluminophosphate Molecular Sieves in Alkaline Media.

Unlike conventional aluminosilicate zeolites synthesized in alkaline media, aluminophosphate molecular sieves (AlPOs) have always been prepared under acidic conditions in the past three decades; this has been regarded as one of essential factors for synthesis, except for the case of silica-substituted analogues (SAPOs). For the first time, we demonstrate herein a simple and generalized route for synthesizing various types of aluminophosphate molecular sieves in alkaline media. A series of aluminophosphate sieves and their analogues have been prepared with different quaternary ammonium cations as structure-directing agents in this manner. The above successes have extended the systematic media from acidic or neutral to alkaline for the preparation of a series of aluminophosphate molecular sieves, which possibly open an alternative route for the synthesis of aluminophosphate molecular sieves.

3D-3D topotactic transformation in aluminophosphate molecular sieves and its implication in new zeolite structure generation

Zeolites have unique pore structures of molecular dimensions and tunable compositions, making them ideal for shape selective catalysis and separation. However, targeted synthesis of zeolites with new pore structures and compositions remains a key challenge. Here, we propose an approach based on a unique 3D-3D topotactic transformation, which takes advantage of weak bonding in zeolites. This is inspired by the structure transformation of PST-5, a new aluminophosphate molecular sieve, to PST-6 by calcination. The structure of nano-sized PST-5 crystals is determined by 3D electron diffraction. We find that the 3D-3D topotactic transformation involves two types of building units where penta- or hexa-coordinated Al is present. We apply this approach to several other zeolite systems and predict a series of new zeolite structures that would be synthetically feasible. This method provides a concept for the synthesis of targeted zeolites, especially those which may not be feasible by conventional methods.

Ionothermal synthesis and characterization of AlPO4 and AlGaPO4 molecular sieves with LTA topology

Abstract Aluminophosphate molecular sieves are recognized as very promising materials for catalysis, adsorption, and separation. This study presented an attempt to synthesize LTA-type AlPO4 and AlGaPO4 molecular sieves by an ionothermal method. The influences of the relevant synthesis parameters and various template removal methods were discussed. The optimum growth temperature, doses of ILs, and crystallization time were suggested. The two-step calcination method was recommended since the intact crystalline structure and microporosity of LTA-type AlPO4 were retained after template removal. Perfect cubic AlPO4-LTA molecular sieves were successfully prepared with an excellent micropore volume of 0.33 ml/g and water uptake of 0.38 g/g at P/P0 = 0.20. Moreover, an LTA-type AlGaPO4 molecular sieve was also successfully synthesized by an ionothermal method with partial Ga doping. Evident changes in morphology were found and could be ascribed to various crystal plane orientations. Ga-doped crystals subjected to template removal and water soaking showed worse thermal and hydrothermal stability. The microporosity and water sorption capacity of AlGaPO4-LTA also decreased greatly due to its sharply reduced stability and collapsed structure. After Ga doping, however, the materials became more hydrophilic, with slightly higher water uptake at low relative pressure. The materials also showed greater acidity strength at both Bronsted and Lewis acid sites.

Facile Synthesis of Hierarchical Nanosized Single‐Crystal Aluminophosphate Molecular Sieves from Highly Homogeneous and Concentrated Precursors

AbstractThe synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single‐crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8‐rings), AEL (10‐rings), AFI (12‐rings), and ‐CLO (20‐rings) topologies, ranging from small to extra‐large pores, were synthesized. These materials show exceptional properties, including small crystallites (30–150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time‐dependent study revealed a non‐classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism.

Facile Synthesis of Hierarchical Nanosized Single-Crystal Aluminophosphate Molecular Sieves from Highly Homogeneous and Concentrated Precursors.

The synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single-crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8-rings), AEL (10-rings), AFI (12-rings), and -CLO (20-rings) topologies, ranging from small to extra-large pores, were synthesized. These materials show exceptional properties, including small crystallites (30-150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time-dependent study revealed a non-classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism.

Simplified ionothermal synthesis of extra-large-pore aluminophosphate molecular sieve with -CLO topology

An extra-large-pore aluminophosphate molecular sieve with -CLO topology was successfully synthesized in low-dosage ionic liquids (ILs) via a simplified ionothermal route, for which all raw materials were firstly mixed together, and then ground into homogeneous gels followed by high-temperature crystallization. A representative -CLO-type sample was characterized by XRD, SEM, N2 physisorption, TG-DSC, CHN elemental analysis and liquid 13C NMR. The results indicate that the synthesis of -CLO topology is through the co-structure directing effect of the ionic liquid 1-ethyl-3-methylimidazolium bromide and diisopropylamine. Moreover, the optimum synthetic conditions of this material were refined. It was found that the appropriate crystallization temperature and time are 190 °C and 2 h, respectively. Owing to the facile preparation procedure and low consumption of ionic liquids, the newly synthesized extra-large-pore -CLO molecular sieve may find potential application in related areas.