Aluminosilicate Zeolites Research Articles

Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY.

The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6-7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C82+ (1,1'-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C82+) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Brønsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.

Direct microwave energy input on a single cation for outstanding selective catalysis.

Microwave (MW)-driven catalytic systems are attracting attention not only as an aggressive electrification strategy of the chemical industry but also as creating a unique catalytic reaction field that conventional equilibrium heating cannot achieve. This study unlocked direct and selective heating of single alkali metal cations in the pores of aluminosilicate zeolites under MW. Selectively heated Cs+ cations in FAU zeolite exhibited selective CH4 combustion performance, that is, COx generation at the heated Cs+ cations selectively occurred while side reactions in the low-temperature gas phase were suppressed. The Cs-O pair distribution function revealed by synchrotron-based in situ x-ray total scattering gave us direct evidence of peculiar displacement induced by MW, which was consistent with the results of molecular dynamics simulation mimicking MW heating. The concept of selective monoatomic heating by MW is expected to open a next stage in "microwave catalysis" science by providing physicochemical insights into "microwave effects."

Illuminating the Black Box: A Perspective on Zeolite Crystallization in Inorganic Media.

ConspectusSince the discovery of synthetic zeolites in the 1940s and their implementation in major industrial processes involving adsorption, catalytic conversion, and ion exchange, material scientists have targeted the rational design of zeolites: controlling synthesis to crystallize zeolites with predetermined properties. Decades later, the fundamentals of zeolite synthesis remain largely obscured in a black box, rendering rational design elusive. A major prerequisite to rational zeolite design is to fully understand, and control, the elementary processes governing zeolite nucleation, growth, and stability. The molecular-level investigation of these processes has been severely hindered by the complex multiphasic media in which aluminosilicate zeolites are typically synthesized. This Account documents our recent progress in crystallizing zeolites from synthesis media based on hydrated silicate ionic liquids (HSIL), a synthesis approach facilitating the evaluation of the individual impacts of synthesis parameters such as cation type, water content, and alkalinity on zeolite nucleation, growth, and phase selection. HSIL-based synthesis allows straightforward elucidation of the relationship between the characteristics of the synthesis medium and the properties and structure of the crystalline product. This assists in deriving new insights in zeolite crystallization in an inorganic aluminosilicate system, thus improving the conceptual understanding of nucleation and growth in the context of inorganic zeolite synthesis in general. This Account describes in detail what hydrated silicate ionic liquids are, how they form, and how they assist in improving our understanding of zeolite genesis on a molecular level. It describes the development of ternary phase diagrams for inorganic aluminosilicate zeolites via a systematic screening of synthesis compositions. By evaluating obtained crystal structure properties such as framework composition, topology, and extraframework cation distributions, critical questions are dealt with: Which synthesis variables govern the aluminum content of crystallizing zeolites? How does the aluminum content in the framework determine the expression of different topologies? The crucial role of the alkali cation, taking center stage in all aspects of crystallization, phase selection, and, by extension, transformation is also discussed. New criteria and models for phase selection are proposed, assisting in overcoming the need for excessive trial and error in the development of future synthesis protocols.Recent progress in the development of a toolbox enabling liquid-state characterization of these precursor media has been outlined, setting the stage for the routine monitoring of zeolite crystallization in real time. Current endeavors on and future needs for the in situ investigation of zeolite crystallization are highlighted. Finally, experimentally accessible parameters providing opportunities for modeling zeolite nucleation and growth are identified. Overall, this work provides a perspective toward future developments, identifying research areas ripe for investigation and discovery.

Direct Detection of Paired Aluminum Heteroatoms in Chabazite Zeolite Catalysts and Their Significance for Methanol Dehydration Reactivity.

The distributions of heteroatoms within zeolite frameworks have important influences on the locations of exchangeable cations, which account for the diverse adsorption and reaction properties of zeolite catalysts. In particular for aluminosilicate zeolites, paired configurations of aluminum atoms separated by one or two tetrahedrally coordinated silicon atoms are important for charge-balancing pairs of H+ cations, which are active for methanol dehydration, or divalent metal cations, such as Cu2+, which selectively catalyze the reduction of NOx, both technologically important reactions. Such paired heteroatom configurations, however, are challenging to detect and probe, due to the typically nonstoichiometric compositions and nonperiodic distributions of aluminum atoms within aluminosilicate zeolite frameworks. Nevertheless, distinct configurations of paired framework aluminum atoms are unambiguously detected and resolved in solid-state 2D 27Al-29Si and 29Si-29Si NMR spectra, which are sensitive to the local environments of covalently bonded 27Al-O-29Si and 29Si-O-29Si moieties, respectively. Specifically, two H+-chabazite zeolites with the same bulk framework aluminum contents are shown to have different types and populations of closely paired aluminum species, which correlate with higher activity for methanol dehydration. The methodologies and insights are expected to be broadly applicable to analyses of heteroatom sites, their distributions, and adsorption and reaction properties in other zeolite framework types.

Design of an Organic Template for Synthesizing ITR Zeolites under Ge-Free Conditions.

Germanosilicate zeolites with various structures have been extensively synthesized, but the syntheses of corresponding zeolite structures in the absence of germanium species remain a challenge. One such example is an ITR zeolite structure, which is a twin of the ITH zeolite structure. Through the modification of a classic organic template for synthesizing ITH zeolites and thus designing a new organic template with high compatibility to ITR zeolite assisted by theoretical simulation, we, for the first time, show the Ge-free synthesis of an ITR structure including pure silica, aluminosilicate, and borosilicate ITR zeolites. These materials have high crystallinity, corresponding to an ITR content of more than 95%. In the methanol-to-propylene (MTP) reaction, the obtained aluminosilicate ITR zeolite exhibits excellent propylene selectivity and a long lifetime compared with conventional aluminosilicate ZSM-5 zeolite. The strategy for the design of organic templates might offer a new opportunity for rational syntheses of novel zeolites and, thus, the development of highly efficient zeolite catalysts in the future.

Novel 3D-Printed Biocarriers from Aluminosilicate Materials

The addition of biocarriers can improve biological processes in bioreactors, since their surface allows for the immobilization, attachment, protection, and growth of microorganisms. In addition, the development of a biofilm layer allows for the colonization of microorganisms in the biocarriers. The structure, composition, and roughness of the biocarriers’ surface are crucial factors that affect the development of the biofilm. In the current work, the aluminosilicate zeolites 13X and ZSM-5 were examined as the main building components of the biocarrier scaffolds, using bentonite, montmorillonite, and halloysite nanotubes as inorganic binders in various combinations. We utilized 3D printing to form pastes into monoliths that underwent heat treatment. The 3D-printed biocarriers were subjected to a mechanical analysis, including density, compression, and nanoindentation tests. Furthermore, the 3D-printed biocarriers were morphologically and structurally characterized using nitrogen adsorption at 77 K (LN2), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The stress–strain response of the materials was obtained through nanoindentation tests combined with the finite element analysis (FEA). These tests were also utilized to simulate the lattice geometries under compression loading conditions to investigate their deformation and stress distribution in relation to experimental compression testing. The results indicated that the 3D-printed biocarrier of 13X/halloysite nanotubes was endowed with a high specific surface area of 711 m2/g and extended mesoporous structure. Due to these assets, its bulk density of 1.67 g/cm3 was one of the lowest observed amongst the biocarriers derived from the various combinations of materials. The biocarriers based on the 13X zeolite exhibited the highest mechanical stability and appropriate morphological features. The 13X/halloysite nanotubes scaffold exhibited a hardness value of 45.64 MPa, which is moderate compared to the rest, while it presented the highest value of modulus of elasticity. In conclusion, aluminosilicate zeolites and their combinations with clays and inorganic nanotubes provide 3D-printed biocarriers with various textural and structural properties, which can be utilized to improve biological processes, while the most favorable characteristics are observed when utilizing the combination of 13X/halloysite nanotubes.

Fe- and Cu–Zn-Containing Catalysts Based on Natural Aluminosilicate Nanotubes and Zeolite H-ZSM-5 in the Hydrogenation of Carbon Dioxide

Iron- and Cu–Zn-containing carbon dioxide hydrogenation catalysts based on natural aluminosilicate nanotubes and zeolite H-ZSM-5 are synthesized. Their textural and acidic properties are studied via low-temperature nitrogen adsorption–desorption, temperature-programmed desorption of ammonia, temperature-programmed reduction of hydrogen, and elemental analysis. The effect the temperatures of the reaction have on the conversion of CO2 and distribution of its product is studied. Catalysts based on aluminosilicate halloysite nanotubes exhibit methanol and С2–С4 hydrocarbon selectivities of 88 and 16%, respectively.

Fe- and Cu–Zn-Containing Catalysts Based on Natural Aluminosilicate Nanotubes and Zeolite H-ZSM-5 in the Hydrogenation of Carbon Dioxide

Fe- and Cu–Zn-Containing Catalysts Based on Natural Aluminosilicate Nanotubes and Zeolite H-ZSM-5 in the Hydrogenation of Carbon Dioxide

Application of zeolite based nanocomposites for wastewater remediation: Evaluating newer and environmentally benign approaches

The presence of heavy metal ions and emerging pollutants in water poses a great risk to various biological ecosystems as a result of their high toxicity. Consequently, devising efficient and environmentally friendly methods to decontaminate these waters is of high interest to many researchers around the world. Among the varied water treatment and desalination means, adsorption and photocatalysis have been widely employed. However, the discussion and analysis of the use of zeolite-based composites as adsorbents are somehow minimal. The porous aluminosilicates (zeolites) are excellent candidates in wastewater treatment owing to various mechanisms of pollutants removal that they possess. The purpose of this review is thus to provide a synopsis of the current developments in the fabrication and application of nanocomposites based on zeolite as adsorbents and photocatalysts for the extraction of heavy metals, dyes and emerging pollutants from wastewaters. The review goes on to look into the effect of weight ratio on photocatalyst, photodegradation pathways, and various factors that influence photocatalysis and adsorption.

Molecular Modification of Zeolites with Cold Atmospheric-Pressure Plasma Jet: A Green and Facile Strategy

Widespread applications of zeolites demand the optimization of crystal size and morphology. Crystal growth modifiers (CGMs) have been proved effective for zeolite rational design, but the additional chemicals raise environmental and safety concerns. Herein, the industry-ready technique of cold atmospheric-pressure plasma jet (CAPPJ) was employed to induce reactive plasma species as green and eco-friendly CGMs. The synthesis mixtures of three aluminosilicate zeolites with assorted Si/Al ratios (SAR), channel dimensionalities, and pore apertures (i.e., MFI, LTA, and LTL framework types) were first subjected to Ar-CAPPJ treatment for up to 30 min during the aging period. Apparent size and shape modifications were successfully achieved for the resulting crystals with the emergence of rounded surfaces implying surface roughening at the molecular level. For the silicoaluminophosphate SAPO-34 (CHA type), the introduction of plasma CGMs was found to propel a phase transformation, promoting the crystallization of SAPO-18 (AEI type) impurity with reduced framework density. Experimental observations seem to suggest that the classical model of CGMs attaching to selected crystal surfaces is less likely to happen. Whereas, the investigation of zeolite L dispersions revealed enhanced concentrations and altered physicochemical properties of soluble species and amorphous precursors, alluding to the potential functional mechanism (s) of plasma CGMs. As a plausible technique to generate green and versatile CGMs, the impacts of CAPPJ on zeolite crystallization are systematically investigated for the first time, promoting the understanding of classical and nonclassical crystallization phenomena during zeolite synthesis.

The influence of zeolite pore topology on the separation of carbon dioxide from methane

The influence of framework topology on the separation of carbon dioxide from methane has been studied in a set of small pore pure silica zeolites with CHA, IHW, ITW, LTA, MTF and RWR structures. To isolate this effect, the composition of the materials has been kept constant by using pure silica materials, which have neither aluminium in their framework nor extraframework cations that can alter the adsorption behaviour. Pure component adsorption isotherms and breakthrough experiments with synthetic mixtures resembling biogas and natural gas have been conducted. Materials Si-RWR and Si-ITW, which present channel-like topology, show higher IAST selectivities towards CO2 due to a kinetic exclusion of methane, which in the case of Si-RWR is pore-size based and in the case of Si-ITW, topology based. High heat of adsorption of CO2 on Si-ITW is explained through a maximisation of the dispersive interactions between the tight channels and the adsorbate. The extremely small pores of Si-RWR lead to a reduced diffusivity not only of CH4 but also of CO2 precluding its use as adsorbent for this separation. Si-ITW arises as a promising material in the separation of CO2 from CH4, having high selectivity towards CO2 while keeping high diffusion rates and a moderate maximum capacity. A comparison of the performance of these materials with that of aluminosilicate zeolites LTA with Si/Al ratio of 5 and 13X shows that Si-ITW can be more convenient by lowering the energetic requirements of the regeneration step. Moreover, the hydrophobicity of this material can be a further advantage over traditional zeolites.

Preparation and characterization of tungsten tailing-based geopolymers

Using tailings to prepare constructive materials is of great significance for sustainable development of mineral processing industry. In this study, the possibility of preparing tungsten tailing-based geopolymers was explored in detail. XRD, FTIR, PLM, SEM and XPS analyses were carried out to characterize the phase composition, chemical bonding, microstructure, chemical state, and interface properties of tungsten tailing-based geopolymers. Results showed tungsten tailings presented little activity using NaOH as activator, while geopolymers with 60% non-pretreatment tungsten tailing and 40% metakaolin presented a 3-day compressive strength of 8.4 MPa and 28-day compressive strength of 9.1 MPa. The geopolymerization products of tungsten tailing-based geopolymers were N-A-S-H gels and aluminosilicate zeolite crystals, while tungsten tailings were wrapped by metakaolin-derived geopolymerization phases as aggregates with interfaces containing Si–O–Si bonding between quartz in tungsten tailings and zeolite and/or gel phase in metakaolin-derived geopolymer in the geopolymerization process. Besides, the leaching test results indicated that the immobilization efficiency of T6M4 geopolymers for Mn and Pb derived from tungsten tailings reached up to 97.28% and 99.95%, respectively. This research results provide a new idea for utilization of tungsten tailings on a large scale.

Removal of Cesium and Strontium Ions from Aqueous Solutions by Thermally Treated Natural Zeolite.

The radionuclides of cesium (Cs) and strontium (Sr) are dangerous products of nuclear fission that can be accidentally released into wastewater. In the present work, the capacity of thermally treated natural zeolite (NZ) from Macicasu (Romania) to remove Cs+ and Sr2+ ions from aqueous solutions in batch mode was investigated by contacting different zeolite quantities (0.5, 1, and 2 g) of 0.5-1.25 mm (NZ1) and 0.1-0.5 mm (NZ2) particle size fractions with 50 mL working solutions of Cs+ and Sr2+ (10, 50, and 100 mg L-1 initial concentrations) for 180 min. The concentration of Cs in the aqueous solutions was determined by inductively coupled plasma mass spectrometry (ICP-MS), whereas the Sr concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The removal efficiency of Cs+ varied between 62.8 and 99.3%, whereas Sr2+ ranged between 51.3 and 94.5%, depending on the initial concentrations, the contact time, the amount, and particle size of the adsorbent material. The sorption of Cs+ and Sr2+ was analyzed using the nonlinear form of Langmuir and Freundlich isotherm models and pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The results indicated that the sorption kinetics of Cs+ and Sr2+ on thermally treated natural zeolite was described by the PSO kinetic model. Chemisorption dominates the retention of both Cs+ and Sr2+ by strong coordinate bonds with an aluminosilicate zeolite skeleton.

Does Water Enable Porosity in Aluminosilicate Zeolites? Porous Frameworks versus Dense Minerals.

Recently identified zeolite precursors consisting of concentrated, hyposolvated homogeneous alkalisilicate liquids, hydrated silicate ionic liquids (HSIL), minimize correlation of synthesis variables and enable one to isolate and examine the impact of complex parameters such as water content on zeolite crystallization. HSIL are highly concentrated, homogeneous liquids containing water as a reactant rather than bulk solvent. This simplifies elucidation of the role of water during zeolite synthesis. Hydrothermal treatment at 170 °C of Al-doped potassium HSIL with chemical composition 0.5SiO2:1KOH:xH2O:0.013Al2O3 yields porous merlinoite (MER) zeolite when H2O/KOH exceeds 4 and dense, anhydrous megakalsilite when H2O/KOH is lower. Solid phase products and precursor liquids were fully characterized using XRD, SEM, NMR, TGA, and ICP analysis. Phase selectivity is discussed in terms of cation hydration as the mechanism, allowing a spatial cation arrangement enabling the formation of pores. Under water deficient conditions, the entropic penalty of cation hydration in the solid is large and cations need to be entirely coordinated by framework oxygens, leading to dense, anhydrous networks. Hence, the water activity in the synthesis medium and the affinity of a cation to either coordinate to water or to aluminosilicate decides whether a porous, hydrated, or a dense, anhydrous framework is formed.

Fast Removal of Tetracycline from Aqueous Solution by Aluminosilicate Zeolite Nanoparticles with High Adsorption Capacity

Aluminosilicate zeolite nanoparticles were synthesized in a water-in-oil solvent and applied as an adsorbent for tetracycline (TC) removal from aqueous solutions. The large specific surface area at 495.8 m2 g–1 confirms that the zeolite nanoparticles have mesopores. The zeolite nanoparticles show an excellent removal efficiency for TC, achieving over 97% in the pH range of 4.70–7.17. A fast adsorption kinetics was observed, reaching equilibrium in only 20 min following a pseudo-second-order kinetic model. The adsorption isotherm was found to follow the Langmuir model, with a maximum adsorption capacity of TC of 454.55 mg g–1 at pH 6.7 with no salt added. After 6 cycles of reuse, the removal efficiency of TC remained high at 90.3%. It was understood that the adsorption process is spontaneous and exothermic, with an activation energy of 37.94 kJ mol–1. The high observed adsorption affinity is attributed to hydrogen bonding between TC and the hydroxyl groups on the zeolite nanoparticles and the formation of outer-sphere surface complexes. This study shows a new way to synthesize aluminosilicate zeolite nanoparticles that are an efficient and recyclable adsorbent for effective removal of TC from contaminated water.

Iodine Capture by Ag-Loaded Solid Sorbents Followed by Ag Recycling and Iodine Immobilization: An End-to-End Process

The article demonstrates the complete process of I2(g) capture using Ag-exchanged faujasite (AgX) and Ag-exchanged mordenite (AgZ) zeolite sorbents, the recovery of Ag for recyclability of iodine capture, and the immobilization of iodide (from the elution process) into an iodosodalite waste form, which is chemically and environmentally stable. The gaseous iodine, I2(g), was captured in the AgX via chemisorption by Ag and converted to AgI within the aluminosilicate zeolite frameworks. The elution reaction in Na2S resulted in the precipitation of Ag2S and dissolution of I– and Na+ into the aqueous solution, where powdered sorbent showed higher conversion efficiency than the granular form, which is attributed to Na2S-solution diffusion limitations in the granules. The Ag2S-containing aluminosilicate precipitates were filtered out of the solution, and the filtrate (aqueous solution) was used to synthesize iodosodalite to immobilize iodide. The iodine capture using the recovered Ag2S-containing sorbents shows equivalent iodine loadings to the AgX starting material of Qe = 0.355 g/g for powdered material and 0.255 g/g for granular material, demonstrating the potential recycling of Ag for iodine capture as Ag2S-based sorbents.

NH4F modified β zeolite for aniline condensation to diphenylamine and its catalytic mechanism

The main factors affecting the performance of solid acid catalyzed liquid-phase condensation of aniline to diphenylamine are acidity and pore structure. Fluorine has strong electron affinity due to its special electronic structure, which can adjust the acidity and pore structure of zeolite. β zeolite was modified with different concentrations of NH4F solution. The aluminum in the framework of aluminosilicate zeolite was removed to a certain extent, and the acidity and pore size of β zeolite were controlled. Combined with XRD, Py-IR, Al MAS NMR and DRIFTS the active center and reaction mechanism of the catalytic reaction were discussed.

The effect of metals on zeolite crystallization kinetics with relevance to nuclear waste glass corrosion

Geologic disposal of vitrified radioactive material is planned in several countries, but there are remaining uncertainties related to the long-term stability of glass exposed to groundwater. Specifically, the crystallization of aluminosilicate zeolite minerals can accelerate the rate at which glass corrodes and radioactive material is released into the biosphere. In this study, we identify elemental species that may accelerate or suppress zeolite formation using a protocol to examine their effects on zeolite synthesis over a three-day duration. Our results are consistent with previous works demonstrating glass corrosion acceleration in the presence of calcium. Furthermore, we identify two elements—tin and lithium—as inhibitors of zeolite P2 (gismondine, or GIS type) nucleation and, thus, promising components for promoting the long-term durability of glass waste forms.

Tailoring zeolite ERI aperture for efficient separation of CO2 from gas mixtures

Constructing the metal cation-mediated low-cost inorganic sorbent with high separation efficiency in CO2, N2, and CH4 remains a major challenge. Herein, we developed a series of alkali metal cations (Na+, K+, Rb+, Cs+)-exchanged ERI zeolites and adopted in the separation process of CO2 among the gas mixture. Among the ion-exchanged zeolites, the zeolite K-ERI showed a high adsorption volume of 70.84 cm3g−1 and an IAST selectivity of CO2/CH4: 6254, CO2/N2: 2872 at 298 K, respectively, far outweighed the reported metal cation exchanged zeolites. Combining powder X-ray diffraction crystallography and density functional theory calculations, we unequivocally unveiled that the metal cations located at s8r effectively tailored zeolite aperture, and metal cation-gas molecules interactions synergically restrained the pass-through capacity of CO2 in ion-exchanged ERI framework. Such a unique host–guest interaction governed by metal cations in aluminosilicate zeolite ERI affords a general strategy for gas separation.

Selective conversion of polyethylene wastes to methylated aromatics through cascade catalysis

Polyethylene was selective converted into methylated aromatics over the catalysts of aluminosilicate MFI zeolite nanosheets (s-ZSM-5) and mesoporous MFI zeolite modified with zinc species (Zn/meso-ZSM-5).