Formation Of Zeolite Research Articles

Effects of alkaline extraction on behavior of rare earth elements in coal ashes.

The effects of alkaline extraction on the behavior of rare earth elements in coal ashes were investigated in the present study. Independent variables are the concentration of extractant and particle size of coal ashes. Sodium hydroxide was used as an extractant, and the molarity of the solvents varied from 1.0 to 7.0M. The coal ashes used here were fly and bottom ashes. Fly and bottom ashes were classified into four samples by particle size, with each categorized at both 45 and 300µm. The particle size distribution and crystalline characteristics of coal ashes, leaching, and the contents of rare earth elements in coal ashes after alkaline extraction were investigated, and the effects of independent variables on the content of rare earth elements in coal ashes were discussed. The test results showed that the dissolution of amorphous phase in coal ashes mainly occurred when the molarity was not more than 3M, while dissolution and precipitation such as geopolymerization and the formation of zeolite occurred simultaneously when the molarity was more than 5M. The dissolution and formation of precipitates such as geopolymer in the present study affected the variation of the rare earth element contents in the ashes. Besides, the ashes being smaller in size was more favorable for an increase in the rare earth elements in coal ashes.

Synthesis and Structure Determination by 3D Electron Diffraction of the Extra‐large Pore Zeolite ITQ‐70

In this study, we present the synthesis, characterization, and structural analysis of a novel zeolite, ITQ‐70, using 3D electron diffraction tomography. This unique material was synthesized under alkaline conditions, employing tetrakis(diethylamino)phosphonium as organic structure‐directing agent, leading to the formation of a pure silica zeolite. ITQ‐70 is distinguished by its extra‐large pore apertures, which extend along all three axes and intersect one to each other. A notable feature of this zeolite is the presence of structurally ordered defects in very high concentration (38% of the silicon atoms). As a result, ITQ‐70 exhibits the lowest framework density (10.0 T/1000Å3) ever reported for any zeolite except RWY (7.6 T/1000Å3), which contains sulfur instead of oxygen connecting T‐atoms.

Synthesis and Structure Determination by 3D Electron Diffraction of the Extra-large Pore Zeolite ITQ-70.

In this study, we present the synthesis, characterization, and structural analysis of a novel zeolite, ITQ-70, using 3D electron diffraction tomography. This unique material was synthesized under alkaline conditions, employing tetrakis(diethylamino)phosphonium as organic structure-directing agent, leading to the formation of a pure silica zeolite. ITQ-70 is distinguished by its extra-large pore apertures, which extend along all three axes and intersect one to each other. A notable feature of this zeolite is the presence of structurally ordered defects in very high concentration (38% of the silicon atoms). As a result, ITQ-70 exhibits the lowest framework density (10.0 T/1000Å3) ever reported for any zeolite except RWY (7.6 T/1000Å3), which contains sulfur instead of oxygen connecting T-atoms.

Role of silicon in the growth of ZSM-5 synthesized with coal fly ash as raw materials

In this work, single-phase ZSM-5 zeolite was synthesized using solid waste coal fly ash (CFA) as raw material, providing a potential alternative for creating high-value-added products from this waste. X-ray diffraction (XRD), scanning electron microscopy, X-ray fluorescence, Fourier transform infrared spectroscopy, N2 physisorption, and other techniques were used to evaluate the crystallization and morphology of the ZSM-5 obtained. The results indicated that ZSM-5 can be synthesized by the simple method of mixing, stirring, and heating. A well-defined hexagonal shape of ZSM-5 with a specific surface area of 162 m2/g and mesoporous structure was obtained at the temperature of 160 °C during hydrothermal treatment for 72 h. Theoretically, the mechanism of crystal growth of ZSM-5, i.e. the liquid phase nucleation and step growth models, was clarified. These results open the possibility of exploring the crystallization of ZSM-5 and the utilization of CFA. Simultaneously, the critical roles of silicon in framework formation and crystallization control during the formation and growth of zeolites were elucidated.

Synthesis Method and Principle of Octahedral Hierarchical LTA Zeolite and Its Application to Enhance Catalytic Activity in Styrene Epoxidation.

A 4 Å zeolite prepared under the synergistic effect of intense ultrasound and a high-voltage electrostatic field had an octahedral structure rather than a conventional hexahedral structure. XPS and XRD analyses showed that the ratio of silicon to aluminum, 2θ peak position, and the corresponding crystal planes were the same as those in traditional hexahedral 4 Å zeolite, but some crystal planes were more prominent. SEM imaging showed that the octahedral zeolites had a larger particle size. Porosimetry (BET surface area and BJH analysis) showed that the octahedral zeolite had become a mesoporous zeolite, and its specific surface area increased and its pore size expanded, which was conducive to loading catalytically active materials and thus improving its catalytic performance. In this paper, the mechanism of formation of hierarchical LTA zeolite is discussed, and the octahedral hierarchical LTA zeolite is used to catalyze the epoxidation of styrene, giving very good results. It is concluded that the (600), (622), (642), and (644) crystal planes played a decisive role in the styrene epoxidation reaction, providing a realistic basis for explaining the crystal plane catalysis effect of the 4 Å zeolite. This new zeolite prepared under the synergistic effect of intense ultrasound and a high-voltage electrostatic field, being the first time to prepare the octahedral hierarchical LTA zeolite, is simple to produce, green, and environmentally friendly and has good economic development prospects compared to the use of templating agents, which not only provides ideas and simpler methods for optimizing the performance of traditional zeolites and developing new zeolites with better performance but also enhances the theoretical basis for preparing new zeolites.

Waste Symbiosis through the Synthesis of Highly Crystalline LTA and SOD Zeolites.

In recent years, the demand for natural and synthetic zeolites has surged due to their distinctive properties and myriad industrial applications. This research aims to synthesise crystalline zeolites by co-recycling two industrial wastes: salt slag (SS) and rice husk ash (RHA). Salt slag, a problematic by-product of secondary aluminium smelting, is classified as hazardous waste due to its reactive and leachable nature, though it is rich in aluminium. Conversely, RHA, an abundant and cost-effective by-product of the agro-food sector, boasts a high silicon content. These wastes were utilised as aluminium and silicon sources for synthesising various zeolites. This study examined the effects of temperature, ageing time, and sodium concentration on the formation of different zeolite phases and their crystallinity. Results indicated that increased Na+ concentration favoured sodalite (SOD) zeolite formation, whereas Linde type-A (LTA) zeolite formation was promoted at higher temperatures and extended ageing times. The formation range of the different zeolites was defined and supported by crystallographic, microstructural, and morphological analyses. Additionally, the thermal behaviour of the zeolites was investigated. This work underscores the potential to transform industrial waste, including hazardous materials like salt slag, into sustainable, high-value materials, fostering efficient waste co-recycling and promoting clean, sustainable industrial production through cross-sectoral industrial symbiosis.

Monitoring the dynamics of nanozeolite formation by combined in situ coherent small angle X-ray scattering techniques

Understanding the dynamics of zeolite formation is key to synthesising high-quality zeolitic materials with controllable properties, in order to develop more efficient and performant materials. X-ray photon correlation spectroscopy (XPCS) using coherent X-rays offers new possibilities for in situ observation of nano to micron-scale fluctuation dynamics during crystal growth. An in situ cell, which is capable of collecting time-resolved coherent X-ray scattering data under hydrothermal conditions has been developed and used to study, by in situ XPCS combined with small and wide angle X-ray scattering, zeolite formation and dynamics. Analysis of the results using two-time correlations enables to accurately identify the successive growth and crystallisation steps, revealing the dissolution process of the LTA topology during the SOD growth. This approach opens a powerful new avenue for studying the dynamics of nanomaterials formation, phase transitions and growth processes under in situ conditions that will enable profound insights into the nanoscale synthesis mechanisms.

Lysine-assisted synthesis of plate-like TS-1 zeolite for 1-hexene epoxidation

Plate-like TS-1 zeolites offering a short diffusion pathway along the b-axis are highly desirable catalysts in the reaction of alkene epoxidation. Herein, we successfully developed a simple synthetic strategy toward reducing the thickness along the b-axis of TS-1 zeolite crystals, l-lysine adopted as a zeolite growth modifier was firstly proposed to prepare plate-like TS-1 zeolite. Meanwhile, through tuning the preliminary aging time, plate-like TS-1 zeolites with thickness in the range of 80–1000 nm can be controllable obtained. In this work, the synthesis parameters controlling the formation of plate-like TS-1 zeolites are studied, and the factors controlling the zeolite growth were well elucidated. Compared with the conventional TS-1 zeolite as well as the plate-like TS-1 synthesized in the fluoride-containing medium, the obtained plate-like TS-1 shows improved catalytic performances in catalyzing epoxidation of 1-hexene.

Red mud treated with KOH: synthesis of sustainable materials from waste for water treatment.

Solid waste resulting from bauxite ore (red mud) was converted into useful products consisting in hydrogarnet together with zeolite. Red mud (RM) transformation from disposal material into new source was carried out using potassium hydroxide as an activator and hydrothermal process (HY) or vapor phase crystallization (VPC) approach. HY process was performed at 60, 90, and 130°C whereas during the VPC method, red mud was contacted only with vapor from the distilled water heated at 60 and 90°C. The results indicate the formation of katoite and zeolite L (LTL topology) with both approaches. All the synthetic products display magnetic properties. In addition, a preliminary investigation on arsenic removal from drinking water (from 59 to 86%), makes the synthetic materials appealing for environmental applications. Finally, the synthesis of a large amount of very useful newly-formed phases using vapor molecules confirms the efficiency of the innovative and green VPC process in waste material transformation.

Synthesis of AlPO-18 Zeolite Membrane by Sonication-Assisted Hydrothermal Method for H2 Separation from Blast Furnace Flue Gas

In this study, AlPO-18 zeolite has been synthesized at temperatures ranging from 140° to 180°C and varying synthesis time from 3 to 20 h using sonication mediated hydrothermal process. The characterization results of the synthesized powders and membranes revealed that phase pure AlPO-18 zeolite has been formed at 150°C for 15 h under sonication energy of 250 W. For comparison, the same has been synthesized by the conventional method for 200°C and 69 h. In the sonochemical process, H2O molecule splits into hydrogen radicals (H•) and hydroxyl (•OH) radicals with intense local heating and high pressure during the collapsing of cavitation, which initiates the formation of dihydrogen phosphite (H2PO3•) and dihydrogen phosphate (H2PO4•) radicals and facilitate the formation of AlPO-18 zeolite. Finally, the performance of the membranes has been studied with varying feed pressures for different binary gas mixtures and single gases, and simulated blast furnace (BF) gas has been used to study the separation efficiency of the membranes. The highest separation factors, calculated from BF mixture gas of H2/CO2 and H2/N2 have been achieved as 8.7 and 21, respectively. These results show the possibility of hydrogen recovery from BF flue gas to convert waste to wealth.

Zeolite Synthesis from Natural Kaolin: The Effect of Metakaolin Heating and Transformation

In this study, the effect of kaolin heating and metakaolin transformation on zeolite synthesis was investigated. Two different metakaolin temperatures at the early stage of transformation were chosen in determining the lowest temperature that was capable of synthesizing the zeolite structure from natural kaolin. The synthesis of zeolite materials from the transformation of natural kaolin to metakoalin was conducted through the hydrothermal method. Natural kaolin obtained from Ipoh, Perak, was calcined at two different calcination temperatures of 600°C and 650°C. Metakaolin was obtained after 2 hours of exposure at 600°C and 650°C, respectively, with slightly different FTIR peaks of quartz at both temperatures. The incomplete metakaolin formation at a slightly lower temperature revealed the unsuccessful zeolite formation. At slightly higher calcination temperatures, the metakoalin peak obviously existed and led to the formation of the complete zeolite phase.This experiment also proved the importance of accurate calcination temperature in converting to zeolite synthesis. Furthermore, this current work also revealed that the complete transformation of metakoalin that can be conducted slightly lower temperature as compared to the common metakoalin phase will minimize energy consumption during the zeolite synthesis as well as the metakoalin transformation.

Effect of the introduction of Zn on the electronic state of copper species in Cu-exchanged mordenite

This work evaluated the effect of Zn on the electronic state of copper in the Cu-Zn-mordenite binary system. The samples were prepared in two stages by sequential ion exchange of the initial sodium mordenite, using aqueous solutions of sulfate salts of these two metals, and changing the order of introduction of each of the cations, first Cu2+ and then Zn2+, or in the inverse order. The content of Zn and Cu changed within the 0.02–3.14 wt% interval at various Zn/Cu ratios. The prepared samples were characterized with UV–Vis spectroscopy in situ during temperature-programed oxidation (TPO) in oxygen, temperature-programed reduction (TPR) in hydrogen, and temperature-programed adsorption and desorption of NO (TPD). Cu and Zn have different affinities to mordenite, resulting in competition between them for zeolites sites, their redistribution, and formation of bimetallic Cu-O-Zn species. The order of ion-exchange makes it possible to modify the nature and the relative content of these metal species. Electronic properties of the resulting copper species strongly depend on both the Zn/Cu ratio and the order of exchange of metal ions. The knowledge we have obtained will be useful for designing of new effective catalysts based on copper-exchanged zeolites.

Acceleration of Zeolite Crystallization: Current Status, Mechanisms, and Perspectives.

Zeolites are important classes of crystalline materials and possess well-defined channels and cages with molecular dimensions. They have been extensively employed as heterogeneous catalysts and gas adsorbents due to their relatively large specific surface areas, high pore volumes, compositional flexibility, definite acidity, and hydrothermal stability. The zeolite synthesis normally undergoes high-temperature hydrothermal treatments with a relatively long crystallization time, which exhibits low synthesis efficiency and high energy consumption. Various strategies, e.g., modulation of the synthesis gel compositions, employment of special silica/aluminum sources, addition of seeds, fluoride, hydroxyl (·OH) free radical initiators, and organic additives, regulation of the crystallization conditions, development of new approaches, etc., have been developed to overcome these obstacles. And, these achievements make prominent contributions to the topic of acceleration of the zeolite crystallization and promote the fundamental understanding of the zeolite formation mechanism. However, there is a lack of the comprehensive summary and analysis on them. Herein, we provide an overview of the recent achievements, highlight the significant progress in the past decades on the developments of novel and remarkable strategies to accelerate the crystallization of zeolites, and basically divide them into three main types, i.e., chemical methods, physical methods, and the derived new approaches. The principles/acceleration mechanisms, effectiveness, versatility, and degree of reality for the corresponding approaches are thoroughly discussed and summarized. Finally, the rational design of the prospective strategies for the fast synthesis of zeolites is commented on and envisioned. The information gathered here is expected to provide solid guidance for developing a more effective route to improve the zeolite crystallization and obtain the functional zeolite-based materials with more shortened durations and lowered cost and further promote their applications.

Experimental verification of double-four-ring-type aluminosilicate molecule as a single-source precursor for zeolite synthesis

Abstract While a variety of functional zeolites have been synthesized using hydrothermal methods with conventional discrete Al and Si sources, control of the composition, structure, and function of the targeted zeolites often involves expensive and time-consuming trial-and-error approaches. Despite ongoing efforts to manipulate zeolite formation by adjusting Al and Si sources and reaction conditions, limited attention has been given to studies on zeolite synthesis using molecular precursors (MPs) with preorganized Al–O–Si bonds. Here, we demonstrate the synthesis of LTA-type zeolites using [TMA]4[Al4Si4O12(OH)8]·13H2O ([MP]; TMA = tetramethylammonium cation) with a double-four-ring (D4R)-type core structure, which is known to be a secondary building unit in the LTA-type zeolite, as a MP. Here, we demonstrate the successful synthesis of LTA-type zeolites using [MP] under hydrothermal conditions at 100 to 200 °C in the presence of 1 equiv. of NaOH or NaCl. Notably, when discrete Al and Si sources were used instead of [MP] under otherwise identical conditions (the same Si/Al ratio, Na+ content, and temperature), GIS-, SOD-, and FAU-type zeolites lacking the D4R structure were obtained in addition to the LTA-type zeolites.

Assessment of the Swelling Behavior of NaOH-Contaminated Red Earth in the Visakhapatnam Region of India Using X-ray Diffraction Analysis

Research on the impact of alkali contamination on the swelling behavior of red earth in the Visakhapatnam region has been notably limited. Therefore, this study aims to investigate the effects of alkali (NaOH) contamination on the swelling characteristics of the region’s red earth. The red earth of this region was found to be a well-graded sandy soil with 81% sand and 18% fines. X-ray diffraction studies showed that this region’s red earth mainly consists of quartz, kaolinite, and hematite. The soil is inherently non-swelling. However, the free swell tests showed considerable swell under contamination of NaOH solutions of various normalities (0.05, 0.1, 1, 2, and 4N). One-dimensional consolidation tests have shown that the swell increased with the concentration of the NaOH solution and with the duration of the interaction. Red earth exhibited 'an equilibrium swelling' of 5.6, 10, 15, 17, and 20% when contaminated with 0.05, 0.1, 1, 2, and 4N NaOH solutions, respectively. XRD studies revealed that the red earth sample contaminated with even 0.05N NaOH solution and cured for 56 days exhibited the formation of zeolites analcime and natrolite. Silicate minerals like paragonite and ussingite were also formed along with the zeolites. N-A-S-H compounds, hydrosodalites, and zeolites like super hydrated natrolite, zeolite SSZ16, and zeolite ZK-14 were formed at higher normalities of NaOH after a curing period of 56 days, which caused increased swell. The research demonstrated that the formation of zeolites resulting from the alkali contamination led to swelling in the red earth.

Investigating the role of geochemistry and geotechnical properties in landslide characterization and triggering mechanisms: A case study from Dir Upper, Khyber Pakhtunkhwa Pakistan

The 83.5 km Chukyatan-Kumrat Upper Dir road plays a crucial role in transportation and tourism in North Pakistan. Despite its significance, the area faces frequent landslides due to hydrometeorological hazards, posing a threat to its stability. This study conducts the first extensive investigation of landslide susceptibility in the region, considering geological features, geotechnical properties, and rock weathering. The road traverses diverse rock formations, including meta-volcanics, andesites, meta-rhyolites, ignimbrites, volcanic ash, granodiorites, and spotted slates, overlain by residual soils. The presence of the Dir fault has led to significant accumulations of loose, weathered rock debris (>100 m deep). Exposed slopes exhibit polygonal stress fractures, joints, and fissures with steep inclinations (>40°), further enhancing instability. Geotechnical analysis reveals a low internal friction angle (28.5°–31.9°) and cohesion (4.1–5.9 kPa) of slope materials, indicating poor shear resistance compared to stable slopes. The unconfined compressive strength of bedrock (10.7–41.5 MPa) ranges from weak to moderate-strong, emphasizing the contribution of weaker rock formations to instability. Acidic soil pH (3.1–4.2) and clay minerals support the prevalence of weathering conditions promoting landslides. Thin section analysis and X-ray diffraction reveal hydrothermal alteration during low-grade metamorphism, leading to the formation of chlorite, smectite, montmorillonite, and zeolites. Additionally, physical weathering has increased quartz content, potentially impacting slope stability. The combined effect of factors such as steep slope geometry, low shear strength with strain-softening properties, rainfall, snowmelt, freeze-thaw activity, slope base cutting for road development, and massive loading from houses contributes to numerous landslides in the region. The study aids effective mitigation and preparedness in the Chukyatan-Kumrat area and offers insights for landslide susceptibility mapping in similar geological settings.

Synthesis‐structure‐catalysis relations in CHA zeolites applied for selective catalytic reduction of NOx with ammonia

Microporous aluminosilicate zeolites are useful industrial catalysts. However, their hydrothermal synthesis is a multistep process with complicated and unclear reactions, limiting their rational functional design. Herein, we compare the formation pathway and the structural and catalytic properties of several CHA zeolites to obtain fundamental knowledge for intentionally controlling the catalytic function of zeolites. Three CHA zeolites were synthesized using different starting silica/alumina sources in the presence of tetraethylammonium hydroxide as an inexpensive organic structure‐directing agent. FAU zeolite and an amorphous synthesis gel prepared using two different methods were used as starting materials. The obtained CHA zeolites were applied for exhaust gas purification (selective catalytic reduction of NOx with ammonia, NH3‐SCR), and their structural characteristics and formation pathways were investigated using a combination of analytical methods. Stepwise gel preparation (SGP), which divides the compositional control of the amorphous synthesis gel, promotes the decomposition of the initial additive (zeolite seed), resulting in the formation of CHA zeolites with abundant micropores and paired Al sites. This structural feature obtained using the SGP method improves the catalytic durability of the NH3‐SCR reaction. The present relationship, including different crystallization phenomena, structures, and catalytic abilities, provides useful insights into rational zeolite synthesis and its application.

Interchain-expanded extra-large-pore zeolites.

Stable aluminosilicate zeolites with extra-large pores that areopen through rings of more than 12 tetrahedra could be used to process molecules larger than those currently manageable in zeolite materials. However, until very recently1-3, they proved elusive. In analogy to the interlayer expansion of layered zeolite precursors4,5, we report a strategy that yields thermally and hydrothermally stable silicates by expansion of a one-dimensional silicate chain with an intercalated silylating agent that separates and connects the chains. As a result, zeolites with extra-large pores delimited by 20, 16 and 16 Si tetrahedra along the three crystallographic directions are obtained. The as-made interchain-expanded zeolite contains dangling Si-CH3 groups that, by calcination, connect to each other, resulting in a true, fully connected (except possible defects) three-dimensional zeolite framework with a very low density. Additionally, it features triple four-ring units not seen before in any type of zeolite. The silicate expansion-condensation approach we report may be amenable to further extra-large-pore zeolite formation. Ti can be introduced in this zeolite, leading to a catalyst that isactive in liquid-phase alkene oxidations involving bulky molecules, which shows promise in the industrially relevant clean production of propylene oxide using cumene hydroperoxide as an oxidant.

Material design of geopolymers using calcined allophane

As kaolinite, the main material of geopolymers, is not produced in East Asia and elsewhere, it is necessary to find alternative materials to replace kaolinite. The authors therefore investigated the preparation conditions and optimum curing temperature of geopolymers using allophane, which is not used as a cementitious material. Based on compressive strength and internal temperature history results, specimens were prepared by mixing allophane calcined at 800 °C for 3 h with an alkaline solution adjusted to a Na2O/SiO2 ratio of one at a water-to-powder ratio of two. Powder X-ray diffraction and nuclear magnetic resonance spectral analyses of specimens indicated that amorphous geopolymers with a three-dimensional structure were produced from calcined allophane. As for the optimum curing temperature, the samples cured at 20 °C showed the best strength development properties. On the other hand, specimens cured at 80 °C showed a temporary decrease in compressive strength as zeolite formation progressed with increasing curing time. Since 20 °C is the optimal curing condition, we conclude that geopolymers that can be used for on-site curing can be produced by using calcined allophane.

Controllable interlayer hydroxyl condensation of MWW zeolite and its alkylation performance of benzene with ethylene

MWW zeolite holds great promise in the petrochemical industry. However, achieving precise control over its dimension and interlayer hydroxyl condensation remains challenging when using a single, low-toxicity, readily available template. In this study, the rational and targeted hydrothermal synthesis of two-dimensional (2D) MCM-22(P) and three-dimensional (3D) MCM-49 using low-toxic piperidine is realized. The synergistic effect of the organic template and inorganic ions plays a crucial role in the precise synthesis of 2D and 3D MWW zeolite. In contrast to the traditional hexamethyleneimine template, piperidine introduces a distinct characteristic whereby disordered MWW layers coexist with the synthesized products. Specifically, the higher concentration of Na+ species directs more Al species to locate in the T1 site, promoting the condensation of interlayer hydroxyl and leading to the formation of 3D MWW zeolite. In contrast, a system with abundant PI can suppress the condensation of interlayer hydroxyl, resulting in the formation of 2D MWW zeolite. H-MCM-49 synthesized exhibits higher ethylene conversion and ethylbenzene selectivity than H-MCM-22 in the liquid alkylation of benzene and ethylene.