Recent Developments in Zeolite-like Materials Synthesis and Characterisation

In the last few years considerable effort has been directed at the targeted synthesis of zeolites and zeolite-like microporous materials with predetermined physical and catalytic properties. With new computational techniques, it has become possible to design templates for the synthesis of specific microporous structures with desired pore siže and connectivities. With regard to zeolite-like materials, much attention has been focused on transition metal containing systems, like zincosilicates, titanosilicates and various metalloaluminophosphates with a potential to generate specific redox conditions, in addition to Br0nsted and Lewis active catalytic centres. Experimental determination of subtle structural features such as the nature and position of the catalytically active metal sites, and the location, orientation and disorder of templates, metals or complexes within the microporous hosts has become possible using new characterisation techniques, mostly based on X-ray diffraction and the use of synchrotron and neutron radiation sources. In situ studies of the kinetics of nucleation, crystal growth and phase transitions or catalyst activation and operation at elevated temperatures have remarkably benefited from the new high-flux and well-collimated third-generation synchrotron radiation sources, and from the advances in the X-ray detector design and data handling

Isomorphous Substitution of Framework Atoms by Titanium in VPI-5 Aluminophosphate Molecular Sieve

Extra-large pore aluminophosphate molecular sieve TiVPI-5 was synthesised hydrothermally in the presence of di-n-butylamine and transformed by the calcination process at 500 °C to a large pore TAPO-8. Incorporation of titanium(IV) into VPI-5 framework was studied by elemental and thermogravimetric analyses, combined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and UV-VIS absorption spectroscopy. We found that titanium(IV) incorporated in TiVPI-5 isomorphously substitutes framework aluminium on octahedral sites and that it is not present in the structure in the form of TiO2 anatase. In situ IR measurements of pyridine adsorption/desorption were used to check the presence of catalytically active centres in the product resulting from titanium incorporation into the VPI-5 framework. Weak Lewis and Brønsted acid sites were found in small amounts in the calcined product TAPO-8

On a Possible Role of Dicarboxylate Ions in the Formation of Open-framework Metallophosphates

Three dicarboxylic acids (oxalic, malonic and terephthalic) were investigated as possible pillars in the formation of metallophosphates with extended structures in the presence of 1,2-diaminopropane (DAP) as a structure-directing agent. Only the oxalate ion was proven to be a suitable building block in the formation of hybrid networks. The terephthalate ion seems to possess the ability to be structurally involved in lattice formation, although not in networks of the hybrid type. The malonate ion in this system showed no propensity towards lattice formation, i.e., malonic acid merely exits as an intercalated species inside the 2–D zincophosphate structure. Different pillar-functioning ability has been attributed to structural differences of the three dicarboxylate ions

On a Possible Role of Dicarboxylate Ions in the Formation of Open-framework Metallophosphates

Three dicarboxylic acids (oxalic, malonic and terephthalic) were investigated as possible pillars in the formation of metallophosphates with extended structures in the presence of 1,2-diaminopropane (DAP) as a structure-directing agent. Only the oxalate ion was proven to be a suitable building block in the formation of hybrid networks. The terephthalate ion seems to possess the ability to be structurally involved in lattice formation, although not in networks of the hybrid type. The malonate ion in this system showed no propensity towards lattice formation, i.e., malonic acid merely exits as an intercalated species inside the 2–D zincophosphate structure. Different pillar-functioning ability has been attributed to structural differences of the three dicarboxylate ions

Synthesis of mesoporous ▫gammagamma▫-alumina support for water composite sorbents for low temperature sorption heat storage

The efficiency of thermochemical heat storage is crucially determined by the performance of the sorbent used, which includes a high sorption capacity and a low regeneration temperature. The thermochemical salt hydrate– γ-alumina composite sorbents are promising materials for this application but lack systematic study of the influence of γ-alumina structural properties on the final storage performance. In this study, mesoporous γ-Al2O3 supports were prepared by solvothermal and hydrothermal synthesis containing a block copolymer (F-127) surfactant to design thermochemical CaCl2 and LiCl composite water sorbents. Altering the solvent in the synthesis has a significant effect on the structural properties of the γ-Al2O3 mesostructure, which was monitored by powder XRD, nitrogen physisorption, and SEM. Solvothermal synthesis led to a formation of mesoporous γ-Al2O3 with higher specific surface area (213 m2/g) and pore volume (0.542 g/cm3) than hydrothermal synthesis (147 m2/g; 0.414 g/cm3). The highest maximal water sorption capacity (2.87 g/g) and heat storage density (5.17 GJ/m3) was determined for W-46-LiCl containing 15 wt% LiCl for space heating, while the best storage performance in the sense of fast kinetics of sorption, without sorption hysteresis, low desorption temperature, very good cycling stability, and energy storage density of 1.26 GJ/m3 was achieved by W-46-CaCl2

New Composite Water Sorbents CaCl2-PHTS for Low-Temperature Sorption Heat Storage: Determination of Structural Properties

Sorption heat storage, as one of low-energy consuming technologies, is an approach to reduce CO2 emissions. The efficiency of such technology is governed by the performance of the applied sorbents. Thus, sorbents with high water sorption capacity and regeneration temperature from 80 to 150 °C are required. Incorporation of hygroscopic salt such as calcium chloride into porous materials is a logical strategy for increasing the water sorption capacity. This work reports the study on the development of composites with PHTS (plugged hexagonal templated silicate) matrix with an average pore size of 5.7 nm and different amounts of calcium chloride (4, 10, 20 wt.%) for solar thermal energy storage. These composites were prepared by wetness incipient impregnation method. Structural properties were determined by X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). CaCl2 was confined in micro- and mesopores of the matrix. The resulting CaCl2-PHTS materials were used for water sorption at 40 °C, showing an increase of maximal water uptake with higher amount of calcium chloride from 0.78 g/g to 2.44 g/g of the dry composite. A small reduction in water uptake was observed after 20 cycles of sorption/desorption between temperatures of 140 °C and 40 °C, indicating good cycling stability of these composites under the working conditions

Tuning size and properties of zinc ascorbate metal-organic framework via acid modulation

One of the biggest advantages of MOFs is the possibility of modifying their properties and tuning their inherent activity (i.e., sorption, storage, catalytic activity etc.). Textural properties can be tuned by manipulating process and compositional parameters, among which, the effect of additives can be even further distinguished among them based on the way they affect these properties. Beyond the effect that additives have on the size and morphology of nanoMOFs, there is also an effect on properties via creating point defects—missing linker and missing node defects. In this study, we investigated the effect of four monotopic acid modulators—formic, acetic, dichloroacetic and propionic acid, their concentration and the heating type (conventional and microwave—MW) on the size, morphology and textural properties of a recently discovered bioNICS1. It was confirmed that the proposed seesaw model for the controlled size of nanoMOF crystals is less applicable in the case of MW-assisted synthesis, in comparison to conventional heating. In the case of formic acid- and propionic acid-modified materials, we demonstrated that the type of additive plays a different role in crystal growth and generation of defects, implying high tunability being crucial for a material’s structure–property performance optimization

Green Solvents as an Alternative to DMF in ZIF-90 Synthesis

The use of green solvents as an alternative to dimethylformamide (DMF) in the synthesis of zeolitic imidazolate framework-90 (ZIF-90) was investigated. Two biobased aprotic dipolar solvents CyreneTM and γ-valerolactone (GVL) proved to successfully replace DMF in the synthesis at room temperature with a high product yield. While the CyreneTM—based product shows reduced porosity after activation, the use of GVL resulted in materials with preserved crystallinity and porosity after activation, without prior solvent exchange and a short treatment at 200 °C. The primary particles of 30 nm to 60 nm in all products further form agglomerates of different size and interparticle mesoporosity, depending on the type and molar ratios of solvents used