Aluminum-rich Zeolite Research Articles

Zeoliti i njihova primjena u zaštiti bilja

Zeolites are a large group of aluminosilicate minerals that appear in non-metamorphic rocks or are synthesized by humans. Interest in the use of zeolites in agricultural production has been growing in recent years, primarily because they are environmentally friendly. They are used to protect the plants from insects in open areas, as well as in warehouses. Research is being conducted on the effectiveness of zeolite in controlling the insect eggs, larvae, and adults, the cause of plant diseases, and weeds. The movement of insects on the treated parts of the plant is difficult because the zeolite particles are caught by their hairs, making it difficult for them to feed, so they eventually die. Aluminum-rich zeolites are mostly used as the means for drying the surface parts of plants, considering that water is needed for the infections caused by the fungi and bacteria, or they create a thin layer on a leaf surface that prevents the germination of spores and the development of certain plant diseases. Zeolites have a potential to be slowly released, and therefore they ensure that the active substance of the herbicide has a longer duration of effectiveness, whereby a potential for leaching and environmental pollution is being reduced.

Conversion of Harmful Fly Ash Residue to Zeolites: Innovative Processes Focusing on Maximum Activation, Extraction, and Utilization of Aluminosilicate.

Reuse of the solid residue from coal fly ash alumina extraction (FAAE) by acid leaching is problematic. Conversion of this solid residue into aluminum-rich zeolite (13X) and silicon-rich zeolite (ZSM-5) was investigated in this research. The FAAE residue was activated by alkali roasting with Na2CO3 powder (110% mass fraction) at 890 °C for 60 min. Silicon and aluminum were mainly present as two mineral phases, Na2SiO3 and NaAlSiO4, respectively, in the product obtained after roasting. The roasted product was dissolved in water (liquid/solid ratio of 2) after 20 min at 100 °C. The water-leaching liquor was investigated for total conversion to aluminosilicate zeolites without external aluminum or silicon addition. Hydrothermal synthesis of aluminum-rich zeolite 13X was successful after fine tuning of the conditions, although the filtrate had an unusually high SiO2/Al2O3 molar ratio. Production of 13X consumed a large amount of aluminum, which increased the Si/Al ratio to a level suitable for synthesis of ZSM-5. The synthesis of ZSM-5 from the mother liquor of 13X was proved feasible. The FAAE residue was transformed into high-value zeolite products by nearly 100%. Additionally, the tail liquid of this process, mainly containing Na2CO3, was completely recycled. This process could be used to realize high-efficiency and high-value utilization of similar aluminosilicate solid wastes.

Electronic Structure of Zn+-Modified Zeolite: A Density Functional Theory Study of Ferrierite

Density functional theory (DFT) calculations were used to study the monovalent Zn+ cation exchanged in an extra-framework position of zeolite ferrierite. A single Zn+ was found to be paramagnetic. Two Zn+ cations combined to form a subnano-sized dimeric species [Zn–Zn]2+ which fits into the eight- or ten-membered rings (8MR or 10MR, respectively) of ferrierite. Within the [Zn–Zn]2+ pair, two cations were bound via a covalent s–s bond. Upon the pair forming, a huge stabilization was observed, linked with a decrease in potential energy by 235–296 kJ/mol, depending on the location of Zn+ in the framework. The [Zn–Zn]2+ species is an electron paramagnetic resonance (EPR) silent insulator with a band gap of 4.82 eV. Because 8MR and 10MR are present in a majority of zeolite structures, we predict that the Zn-modified electron-rich materials can be fabricated from almost any stable aluminum-rich zeolite. Because of the strong tendency for the conversion of Zn+ to Zn2+, the Zn+-modified zeolites are strong solid ...

Organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite

A series of ZSM-5/ZSM-11 co-crystalline zeolites with various compositions and morphologies were successfully synthesized via an organic template-free hydrothermal route and characterized by XRD, XRF, SEM, NMR and N 2 adsorption/desorption technologies. The effects of raw materials and batch composition were investigated systematically. Various silicon sources can be employed in the organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite, however only a few types of aluminum sources are available. This organic template-free system is favorable to the aluminum-rich zeolite. With the increase of initial SiO 2/Al 2O 3 ratio, the ZSM-5 percentage in the ZSM-5/ZSM-11 co-crystalline zeolite increases as well as the crystal size, and especially the morphology of ZSM-5/ZSM-11 co-crystalline zeolite prepared from the colloidal silica–NaAlO 2 solution system changes gradually from nano-rod aggregation, micro-spindle to single hexagon and then to twinned hexagon crystals. Moreover, Na + and OH − in the initial materials can promote the nucleation of the ZSM-5/ZSM-11 co-crystalline zeolite significantly and are beneficial to the formation of crystals with relatively low length/width ratio, while K + postpones the crystallization process seriously.

Centimeter-sized zeolite bodies of intergrown crystals: Preparation, characterization and study of binder evolution

The control of the inter-particle porosity in polycrystalline zeolite bodies remains a challenge. The present study reports on the preparation of centimeter-sized zeolite bodies (32 × 2 mm pellets) with reduced inter-particle porosity. The bodies were prepared by assembling zeolite colloidal nanocrystals with monomodal particle size distribution and sub-colloidal aluminum hydroxide binder. A secondary growth treatment under hydrothermal conditions was performed in order to fill up the inter-particle voids and obtain polycrystalline zeolite materials with textural characteristics close to those of single zeolite crystals. Initial material, intermediates and ultimate product were studied with a combination of complementary methods revealing a substantial reduction even an elimination of the inter-particle porosity. Particular attention was paid to the chemical evolution of the binder and the migration of aluminum species, employing X-ray powder diffraction, 27Al-MAS, 27Al-3QMAS NMR and X-ray fluorescence spectroscopy analyses. Evidences for insertion of aluminum from the binder into the zeolite framework during secondary growth step were found. Consequently the ultimate pellets comprised aluminum-rich zeolite beta crystals and very low binder content.

Methylammonium-FAU zeolite: Investigation of the basic sites in base catalyzed reactions and its performance

The basicity of methylammonium-faujasite zeolites (FAU) was evaluated in the Knoevenagel and Claisen–Schmidt condensation reactions and in the alcoholysis of propylene oxide with methanol. The basic character of FAU zeolites (Y zeolite with Si/Al = 2.5 and X zeolite with Si/Al = 1.4 ) was systematically altered by incorporating cesium and methylammonium cations, which were located in charge compensation sites. In all three reactions, methylammonium-FAU zeolites showed higher specific activity in comparison to cesium-FAU, indicating that these catalysts encompass stronger basic sites. Characterization of the zeolites has shown that ion exchange of sodium by methylammonium cations reduces their micropore volume, however enhances the strength of their basic sites. TPD-CO 2 experiments demonstrated that aluminum rich zeolites possess higher basicity due to higher number of sites. Additionally, XPS (O1s) measurements illustrated that when monomethylammonium cation is present in ion exchange sites, structural zeolite oxygen anions have a higher basic character in comparison to cesium-FAU. This unique result opens news perspectives for application of these highly basic and low-cost methylammonium molecular sieves in base-catalyzed reactions such as Knoevenagel, Claisen–Schmidt condensation and nucleophilic cleavage of propylene oxide with methanol.

Aluminum-rich zeolite beta incorporated sodium alginate mixed matrix membranes for pervaporation dehydration and esterification of ethanol and acetic acid

Mixed matrix membranes of sodium alginate (NaAlg) were prepared by solution casting by incorporating 2.5, 5, 7.5 and 10 wt.% of zeolite beta particles. The membranes thus prepared were crosslinked with glutaraldehyde and tested for the pervaporation (PV) dehydration of ethanol and acetic acid at 30–60 °C. The aluminum-rich zeolite beta, with its hydrophilic nature as well as molecular sieving effect and its favorable interaction with hydrophilic NaAlg, was responsible to enhance the PV dehydration of acetic acid and ethanol in terms of separation factor, flux, pervaporation separation index (PSI) and enrichment factor ( β). Thermodynamic model for sorption process was investigated typically for water + ethanol mixtures based on Flory–Huggins theory to explain the PV performance. Based on these results, permeance and driving force mechanisms were also elucidated. Extraction or dissolution of zeolite beta from mixed matrix membranes is confirmed by equilibrium sorption. Additionally, the changes in the dimension of pristine and mixed matrix membranes are compared to provide the influence of swelling on the stabilities of mixed matrix membranes. Arrhenius parameters for the process of permeation were calculated using these data at different temperatures to investigate their effects on the nature of the mixed matrix membrane. The plots of ln J p vs. 1/ T were constructed and found to follow the linear trends in the studied range of 30–60 °C for both the feed mixtures, indicating that flux followed the Arrhenius trend. PV experiments were also carried out for 5 and 10 wt.% incorporated NaAlg mixed matrix membranes at 70 °C to verify the suitability of the membranes at the esterification temperature. PV-aided catalytic esterification of acetic acid with ethanol was studied at 70 °C, which led to a considerable increase in ethyl acetate conversion with a reduction in reaction time as compared to the blank reaction due to continuous removal of water permeating through the barrier membrane.

Incorporation of Anthracene into Zeolites: Confinement Effect on the Recombination Rate of Photoinduced Radical Cation‐Electron Pair

FT-Raman spectrometry in combination with diffuse reflectance UV/Vis absorption (DRUVv) and fluorescence emission indicate that complete anthracene (ANT) sorption as intact molecules takes place over 6 months in the medium pores of non-Brønsted acidic M(n)ZSM-5 zeolites (n=0.0, 3.4, 6.6; M=Na+, K+, Rb+, Cs+) with 1 ANT per unit cell loading. The combined effect of confinement and electrostatic field induced by bulky cations (Rb+, Cs+) leads to specific changes in the occluded ANT Raman spectra after very long organization periods (one year). The laser photolysis (266 nm, 355 nm) of ANT@M(n)ZSM-5 equilibrated samples generates long-lived charge separated species in aluminum rich zeolites (n=3.4, 6.6). The very long-lived radical pairs are characterized by conventional DRUVv and CW-EPR spectroscopy. The direct charge recombination rates of ANT.+-electron pairs are dispersive, extending over a broad range of timescales. The kinetic constant values are found to increase dramatically with the aluminum content and increase markedly with M+ according to the following order Na+ < K+ < Rb+ < Cs+. The small reorganization energy (lambda) of ZSM-5 zeolite pores coupled with large negative free energy changes (-DeltaG degrees ) between the ground state ANT oxidation potential and Fermi level of aluminum rich M(n)ZSM-5 explain the observed trends of the ANT.+@M(n)ZSM-5.- charge recombination rates.

X-ray mapping as a tool to characterize mixtures of large zeolite ZSM-5 crystals with amorphous impurities

During the synthesis of large crystals of zeolite ZSM-5 in aluminum-rich gels, two phases formed. Instead of large crystals of aluminum-rich zeolite ZSM-5, ZSM-5 crystals with a relatively low aluminum content and amorphous silica–alumina particles crystallized simultaneously. This was demonstrated using X-ray mapping and NMR spectroscopy.

Synthesis of Al-rich ZSM-12 using TEAOH as template

Hydrothermal synthesis of ZSM-12 (MTW) with tetraethylammonium hydroxide (TEAOH) as template was systematically studied with the objective of obtaining an aluminum rich zeolite. In contrast to other zeolites, published information on the synthesis of ZSM-12, especially aluminum rich samples, is limited since its preparation is a difficult task due to its inherent high silica character. The effect of aluminum content of the gel, the OH −/SiO 2 ratio and the TEA/SiO 2 ratio were examined and the crystallization domain of pure ZSM-12 phase was identified as a function of these parameters. TEA/SiO 2 and OH −/SiO 2 ratios much lower than what is typically used in zeolite synthesis were found to be favorable for crystallization of ZSM-12, especially at Si/Al ratios ranging from 30 to 50. In this study, we were able to successfully synthesize ZSM-12 with Si/Al ratio of 31. This was achieved from gels having TEA/SiO 2 ratios of 0.125 as well as 0.16 and OH −/SiO 2 ratio of 0.07. The products obtained were characterized by XRD, SEM, BET and TGA. The results clearly showed that pure ZSM-12 with high crystallinity was obtained in all the batches. The amount of organic retained in the zeolites after synthesis was constant but the state of TEA was very different depending on the Si/Al ratio of the zeolite.

The chemical vapour and liquid deposition of tetraethoxysilane on ZSM-5, mordenite and beta

The effect of using different silanisation procedures as well as different exposure times and deposition–calcination cycles on the silanisation of three different zeolites, i.e. ZSM-5, mordenite and beta, has been investigated. Tetraethoxysilane (TEOS) was used as a silanisation agent. The three procedures used were chemical vapour deposition (CVD) in a static vacuum system and a vapour phase flow system, respectively, and chemical liquid deposition (CLD). Experiments were carried out with a view to characterising the extent to which the external sites were inertised and the pore openings narrowed. Unidimensional channel structures (e.g. mordenite) or aluminium-rich zeolites (mordenite, beta) were more affected with respect to pore mouth narrowing than the siliceous three-dimensional zeolite ZSM-5. At high temperatures, the presence of water increases the rate of TEOS deposition for zeolites with higher aluminium contents. The adsorbed species resulting from the TEOS deposition reaction or diluents may occupy the pore openings, reducing the extent to which pore mouth blocking occurs. Continuous removal of the adsorbed products resulting from TEOS decomposition results in a faster, less selective deposition. Cyclic TEOS deposition can be used to obtain a more complete coverage by periodic removal of competitively adsorbed species. When agglomerates were crushed after modification, it appeared that acid sites on external surfaces not previously inertised during CVD were exposed, thus partly restoring the external surface acidity.

Towards the Rational Design and Synthesis of Zeolites

AbstractThe mechanisms by which the geometries of organic structure-directing agents are translated into the product pore architectures in the syntheses of pure-silica and high-silica zeolites and of aluminum-rich zeolites are discussed. Two different mechanisms of structure direction and self-assembly via the formation of extended inorganic-organic composite structures or of purelyinorganic structures are proposed for the two different classes of materials. The primary impetus for developing a mechanistic understanding of zeolite synthesis is the ultimate goal of the rational design and synthesis of novel zeolite pore architectures. By considering issues such as hydrophobic hydration behavior of the structure-directing agent and the optimization of inorganic–organic van der Waals interactions, the successful design of structure-directing agents for the synthesis of new zeolite structures may be possible, particularly for high-silica systems.

Limitations of resolution in the 1H magic angle spinning nuclear magnetic resonance spectroscopy of zeolite. Further results

Experimental proof is given for the enhancement of spectral resolution of the 1H MAS NMR spectra of aluminium-rich zeolites by the increase of the resonance frequency (up to 500 MHz) and the spinning rate (up to 11 kHz). Quantum-mechanical calculations are presented which allow a quantitative discussion of the influence of the resonance frequency and the spinning rate on the residual linewidth of the MAS NMR signals of spin-½ nuclei.

On the Loewenstein rule and mechanism of zeolite dealumination

The reason for and the peculiarities of dealumination of aluminum-rich zeolites are explained on the basis of ab initio SCF MO calculations of the energies of local chemical interactions in the zeolite lattice. As distinct from Dempsey-Mikovsky-marshall electrostatic approach (DMM), a conclusion is made that simultaneous extraction of the most closely-situated structural elements from the lattice takes place. The first step of this reaction is their mutual extracoordination according to the scheme. This step and the subsequent formation of large nuclei of hydroxoaluminum phases are regarded as a transformation of the lattice into a most energetically favorable state corresponding to the chemical composition nSiO{sub 2}{center_dot}mAl{sub 2}O{sub 3}{center_dot}kH{sub 2}O. 33 refs., 1 fig., 2 tabs.

Conversion of faujasites to high-silica chabazite SSZ-13 in the presence of N,N,N-trimethyl-1-adamantammonium iodide

The hydrothermal synthetic conversion of aluminium-rich zeolites to organo-zeolites in the presence of N,N,N-trimethyl-1-adamantammonium cations is now extended to the faujasite system. Rates of conversion are seen to be dramatically affected by various treatments of the FAU (faujasite) zeolites. Rates are depressed by steaming FAU zeolites, by ion-exchanging them with unreactive organic cations, or by silylating the surface of the zeolite. Surprisingly, the inhibition is removed by calcining away the organosilyl groups. For a reactive FAU zeolite (Y-62), the extent of conversion was proportional to organo-cation content, with other variables fixed; rates of conversion were also related to hydroxide ion concentration at the start of reaction.