Stability Of Zeolites Research Articles

Studies of the Sorption-Desorption of Pesticides from Cellulose-Based Derivative Nanocomposite Hydrogels

This study analyzed the effect of cellulose derivatives, namely methylcellulose (MC) and carboxymethylcellulose (CMC), on the stability of zeolite in a polymeric solution that would synthesize a three-dimensional network of poly(methacrylic acid)-co-polyacrylamide (PMAA-co-PAAm). Additionally, it investigated the effect of pH on the release of paraquat (PQ) and difenzoquat (DFZ) herbicides. Similar to previous studies with hydrogels containing CMC, the presence of bi and trivalent salts, such as Ca+2 and Al+3, also drastically reduced their swelling degree from 6.7 g/g in NaCl (0.15 mol·L−1) to 2.1 g/g in an AlCl3 solution (0.15 mol·L−1) for the MC nanocomposite. The viscosity results may suggest that the formation of a polysaccharide-zeolite complex contributed to the zeolite stabilization. As for the adsorption results, all samples adsorbed practically the entire concentration of both herbicides in an aqueous solution. Finally, it was also observed that the valence of the salts and molecular weight of the herbicide affect the release process, where DFZ was the herbicide with the highest concentration released. Both nanostructured hydrogels with CMC and MC exhibited lower release at pH = 7.0. These results demonstrated that a more in-depth evaluation of the phenomena involved in the application of these materials in controlled-release systems could help mitigate the impact caused by pesticides.

Mixed‐alkali effect in the thermal collapse and melting kinetics of Zeolite X

AbstractThe thermal stability of zeolites underlies their many applications. Structural collapse usually occurs through a series of reactions, involving an initial low‐density amorphous state (LDA), a high‐density melt (HDA), and, eventually, a dense recrystallization product. The LDA–HDA transition resembles a glass melting process; the HDA phase can sometimes be quenched into a glass. Using isothermal as well as nonisothermal in situ observation methodology on the faujasitic zeolite X and its potassium‐for‐sodium ion‐exchanged derivatives, we find a pronounced mixed‐alkali effect in the characteristic nonisothermal transition temperatures as well as in the isothermal reaction timescale of the LDA–HDA transition. The latter is taken as being directly related to the viscosity of the liquid into which the zeolite framework is melting; the apparent viscosity associated with this melting process was found to reach as high as 1015 Pa.s at 740°C. The observed mixed‐alkali effect is similar to the one observed in the dynamics of common oxide glasses and their corresponding melts.

Zeolite-modified alumina-bead catalyst for hierarchical cracking of bulky molecules

A novel zeolite-modified alumina-bead catalyst (ZSM-5/Al2O3-b) was prepared via calcining zeolite-coated alumina-bead material (Al2O3-b@ZSM-5) to graft zeolitic acid sites on the alumina-bead surface. The acid catalyst proved high activity and more 8 times catalytic efficiency than the corresponding ZSM-5(5 %) + Al2O3 mechanically mixed catalyst for cracking of 1, 3, 5-triisopropylbenzene (TIPB) in the FCC simulation reactor with short contact time. The characterization results showed that the surface property of the alumina-beads has been modified and the interface connection of Si-O-Al bonds between zeolitic nanoparticles and alumina resulted in stable zeolite particles on the alumina surface and the structural stability in hot water. The excellent catalytic performances are ascribed to the decrease of diffusion limitation of reactants and intermediates and the increase of Brønsted acid sites on the ZSM-5/Al2O3-b catalyst. The grafted/modified alumina-bead catalyst can be directly used in practical catalytic cracking of large molecules without forming. This strategy can be extended to the preparation of other types of zeolite-containing catalysts and industrial applications.

Synthesis and tribological assessment of oil-based nanolubricants blended with nano-zeolite for steel–steel contact

This study aims to synthesize zeolite with nano-sized morphology and investigate the tribological performance of nano-zeolite as a lubricating additive dispersed in an oil-based lubricant. Tribological tests were performed and morphologies of wear tracks were characterized to investigate the friction reduction and anti-wear properties of zeolite, respectively. The lubrication mechanism was discussed by illustrating the effects of concentration and particle size on the tribological behavior of zeolite. The optimal concentration of nano-zeolite to improve the tribological performance of the base oil was 2 wt.%, which exhibited a friction reduction of 34.3%. Zeolite particles with larger diameters showed better dispersion stability but worse lubrication performance, which could be concluded from the decrease in the friction reduction ratio. Moreover, the friction coefficient under the lubrication of zeolite at 200°C was 15.8% lower than that of the pure base oil, demonstrating the thermal stability of zeolite. Notably, the application of zeolite resulted in an increase in wear depth due to the occurrence of the three-body abrasion, while the surface asperities of the counterpart were also smoothed in the meantime. This work demonstrates the potential of nano-zeolite to enhance the tribological performance of oil-based lubricants in industrial applications, which could be attributed to their porous structure, lipophilicity, and chemical–thermal stability.

Reinforcement and reconfiguration of framework Al in P@ZSM-5 zeolite via in-situ phosphating strategy for efficient methanol-to-propylene

In this work, a "bottom-up" strategy was proposed to one-step, in-situ synthesize P@ZSM-5 zeolites in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide as a new member of MFI-type zeolite organic templates inventory, and the interaction of phosphorus species with framework aluminum was investigated in detail. Multiple advanced characterizations confirm that the tetrahedrally-coordinated bidentate PIV-O2-AlIV structures are precisely customized and uniformly scattered in the zeolite channels. After experiencing harsh hydrothermal treatment (100 %H2O, 800 °C, 17 h), this new structure endows excellent hydrothermal stability of zeolite (crystallinity retention beyond 95 %) and reinforces its Brønsted acidity. Furthermore, methanol-to-propylene tests show that directly synthetic P@ZSM-5 zeolite performs extraordinarily long lifetime (180 h, WHSV = 1 h−1), enviable propylene selectivity (60.4 %) and propylene/ethylene ratio (ca. 4.3) compared to the counterparts, which is benefited from encouragingly olefinic cycle pathway. These findings afford value-filled opportunities in novel catalyst production mode and understandings for phosphorus-zeolite chemistry. Synopsis-A "bottom-up" strategy was demonstrated to one-step, in-situ synthesize P@ZSM-5 zeolite in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide. The resultant P@ZSM-5 catalyst with hyperuniformly-stable bidentate PIV-O2-AlIV structures exhibited extraordinarily long lifetime (180 h) and enviable propylene selectivity (60.4 %).

Adsorption studies on synthetic lentil-like mordenite for column and batch removal of cadmium and lead ions: investigating isotherms and kinetics

ABSTRACT The mordenite zeolite adsorbent, with a lentil-like structure, was synthesised using a one-step green hydrothermal method. Its textural, structural, and morphological properties were characterised through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and the Brunauer-Emmet-Teller (BET) method. The prepared adsorbent was employed in both continuous and batch adsorption processes to remove toxic Cd(II) and Pb(II) metal ions from aqueous solutions. Operational parameters such as flow rate, initial concentration, and bed height were varied to understand breakthrough time, mass transfer zone, adsorption capacity, and exhaustion time during continuous adsorption, which were investigated and optimised. Additionally, the study explored the influence of solid/liquid ratio, pH, assay time, and initial concentration on batch adsorption. The maximum adsorption capacities of the lentil-like mordenite zeolite in fixed-bed breakthrough experiments were determined to be 78.22 mg/g for Cd (II) ions and 80.82 mg/g for Pb (II) ions. In batch experiments, the capacities were 133.64 mg/g for Cd (II) ions and 239.57 mg/g for Pb (II) ions. Dynamic continuous adsorption isotherms exhibited an excellent fit with the Thomas and Yoon – Nelson models, while batch adsorption isotherms conformed well to the Langmuir model. This study presents a new approach for synthesising high surface area, engineered morphology, reusable, and stable zeolite for effectively adsorbing hard metal ions from wastewaters, contributing to environmental remediation.

Catalytic pyrolysis of high-density polyethylene (HDPE) over hierarchical ZSM-5 zeolites produced by microwave-assisted chelation-alkaline treatment

A new microwave (MW) assisted chelation-alkaline strategy was developed to produce hierarchical ZSM-5 zeolites (with external surface area of 203 m2/g) in minutes, leading to the formation of heterogeneous structure with a high-silica shell and aluminium-rich core (silicon-to-aluminium ratios of 49.2 and 37.6, respectively). The zeolites were assessed comparatively by catalytic pyrolysis of high-density polyethylene (HDPE). Compared to the mesoporous ZSM-5 zeolite prepared by the conventional alkaline treatment (via desilication by the NaOH aqueous solution), the hierarchical zeolite by the MW-assisted method showed comparable kinetics in catalytic pyrolysis of HDPE, but with the improved stability in the cyclic pyrolysis-regeneration tests. The improved stability could be due to the better-preserved structural integrity thanks to the relatively milder surface etching by the MW-assisted chelation dealumination method. In addition, compared to the parent ZSM-5, the product distribution of HDPE catalytic pyrolysis over the hierarchical ZSM-5 zeolite showed a higher portion of oil products (i.e., 12 wt% vs. 6.9 wt%) and an improved alkane-to-olefin ratio in the oil products (2.22 vs. 1.86, respectively) due to the reduced acidity and improved hydrogen transfer ability. The MW-assisted chelation-alkaline treatment could be a new strategy to regulate the trade-off between stability and activity of zeolites for catalytic applications.

Improving mechanical stability of ZSM-5 zeolite by defect-healing treatment

Aluminosilicate zeolites are a group of microporous materials widely used in numerous technical applications as catalysts, adsorbents and ion exchangers. Zeolites are subjected to mechanical stress throughout their lifecycle, resulting in the loss of their crystallinity and micropore volume. Therefore, developing zeolites with excellent mechanical properties is important. Recently, our group has reported a liquid-mediated, defect-healing treatment to eliminate the silanol defects in aluminosilicate zeolites with high Si/Al ratios, resulting in imparting extreme chemical stability against water vapor, one of the major chemical damages to destroy zeolite structures. Herein, we investigate an influence of a liquid-mediated, defect-healing treatment on the intrinsic mechanical features of zeolites. ZSM-5 is selected as the target zeolite in this study. Silanol defects in the parent ZSM-5 (HSZ-890HOA, Tosoh) are eliminated by a liquid-mediated, defect-healing treatment. The parent and healed zeolites are subjected to planetary ball milling to compare their mechanical stabilities. Planetary ball-milling treatments, such as rotation at 600 rpm, degrade the crystalline structures of both the parent and healed ZSM-5 with an increase in duration. The diffraction peaks corresponding to the MFI-type structure in parent ZSM-5 completely diminish after planetary ball milling for 60 min. Conversely, diffraction peaks in healed ZSM-5 were retained after such operations, confirming that the mechanical stability of zeolites was enhanced by the liquid-mediated, defect-healing treatment.

Hierarchical zeolite coatings featuring a spatial gradient architecture for sequentially-controlled bisphosphonate release in the modulation of osteogenic–osteoclastic balance

Osteogenic–osteoclastic microenvironment imbalance impairs osseointegration between joint prostheses and the marrow cavity, which is a crucial contributor to the high incidence of complications such as implant loosening and periprosthetic fractures in osteoporosis (OPs). Previously, we employed hydrogel-based bisphosphonate (BPs) coatings on 3D-printed porous titanium alloy implants (pTi) to modulate the OPs microenvironment through controlled release. However, challenges persisted, including the limited duration of BPs release and associated organic material degradation-induced toxicity. To address these issues, we modified pTi surfaces by introducing chemically stable zeolites and BPs. In this study, we applied Ca2+-functionalized hierarchical zeolite coating on pTi for the first time. By combining mesoporous adsorption and Ca2+ chelation, we achieved efficient encapsulation of zoledronate (ZOL), creating a bioactive interface characterized by a spatial gradient structure with a “microporous-mesoporous-macroporous” morphology. The coating achieves the release of ZOL through the mesoporous structure and facilitates the gradual release of chelated ZOL via ion exchange, resulting in hierarchical drug delivery. Moreover, the spatial gradient structure of the coatings significantly influenced cell extension. Simultaneously, we constructed a bioactive coating with a drug concentration gradient, achieving graded drug release within the microenvironment, which facilitated the accurate regulation of osteogenesis and bone resorption. This coating has the potential to substantially enhance the management of postoperative complications in OPs patients undergoing prosthetic replacement surgery by achieving a balanced osteogenic-osteoclastic response.

Structural Features and Zeolite Stability: A Linearized Equation Approach.

Zeolite stability, in terms of lattice energy, is revisited from a crystal-chemistry point of view. A linearized equation relates the zeolite lattice energy using simple structural data readily available from experiments or modeling. The equation holds for a large range of zeolite energies, up to 3 eV per tetrahedron with respect to quartz, and has been validated internally via two simple machine learning automatic procedures for data fitting/reference partitions and externally using data from recently synthesized zeolites. The approach is certain in locating those recently synthesized zeolites in the energy range of those experimentally known zeolites used in the parametrization of the linearized equation. Hidden intrinsic structural data-energy correlations were found for data sets built from energy-relaxed structures along with energy values computed using the same energy functions employed in the structural relaxation. The asymmetry of the structural features is relevant for an accurate description of the energy.

Oxygen exchange mechanisms in zeolite chabazite under steaming conditions

Under hydrothermal conditions, zeolite frameworks can readily incorporate oxygen from water, via reactive oxygen exchange. This indicates that zeolite frameworks are highly labile and reactive to water, even when stable against full hydrolytic dissolution. However, the routes by which oxygen is exchanged between water and framework have not been established. In this work, we identify the preferable oxygen exchange mechanisms in the zeolite chabazite (CHA) and compare them to hydrolysis and other framework healing mechanisms under the low water concentrations relevant for steaming conditions. We find that oxygen exchange occurs at defect sites that are created by the first hydrolysis step, both in Al–O and Si–O bonds and is competitive with subsequent hydrolysis and non-exchange framework healing processes. Furthermore, we determine the effect of increased water concentration, finding that for both Al–O and Si–O bonds, the second water can either moderately enhance or hinder both hydrolysis and O-exchange, depending on the geometry of the site. This implies that local water concentration is an important factor with varied effects on zeolite stability as a function of water loading. This work provides feasible routes of oxygen exchange in CHA, which together with hydrolytic pathways, govern the stability and mesoporosity of these important porous materials.

Investigating patterns in aluminum distribution and stability in mordenite zeolite structure: Analysis and theoretical conclusions from existing experimental data

Building upon our prior theoretical study, this work focuses on determining the position of the seventh, eighth, and ninth aluminum atoms, along with their respective exchange ▪ cations, within the unit cell of mordenite zeolite. The main objective was to identify the positions of these atoms and cations that correspond to the minimum energy state. As a result, the ground state sequence that describes the order in which aluminum atoms enter in the framework as their number increases was completed. Through our investigation, we were able to derive an analytical expression, based on the Madelung energy, which describes the stability of mordenite zeolite as a function of its Si/Al ratio. This expression provides valuable insights, revealing that as the aluminum content within the framework increases, the stability of the zeolite exhibits an asymptotic decrease. It was found that for the mordenite zeolite, Löwenstein's rule is valid for the full range of Si/Al ratios. Interestingly, the restriction that only one aluminum atom can be accommodated per ζ-cage justifies the nature of the aluminum saturation limit (Si/Al=5) in the mordenite zeolite framework. Furthermore, we conducted an evaluation of the aluminum distribution across various configurations and compared it to different experimental observations. This analysis allowed us to make a comprehensive comparison and draw meaningful insights regarding the distribution patterns of aluminum in the mordenite zeolite.

Study of the Stability of Zeolites in Model Biological Environments

Study of the Stability of Zeolites in Model Biological Environments

Study of the Stability of Zeolites in Model Biological Environments

The stability of synthetic and natural zeolites in model biological media simulating the environment of the stomach (pH 1.8), blood plasma (pH 6.9), and intestines (pH 8) is studied. The effect of long-term exposure (up to 7 days) to biological media on the crystal structure of Beta, Rho, Y, and clinoptilolite zeolites is studied. The degree of degradation of the crystal structure of zeolites is controlled by X-ray phase analysis. Based on the results obtained, conclusions are drawn on the prospects for the use of synthetic and natural zeolites as drug carriers.

Assessment of the stability of LTA zeolites under natural gas drying TSA conditions

The main features in cationic LTA zeolites that are likely to impact its potential hydrothermal stability are interconnected. The Al content and the compensating cation play an important role in the water adsorption but their influence on the zeolite performance in thermal cycles is yet to be understood. In this study, four LTA zeolite samples were synthetized with distinct Si/Al ratios in sodium and potassium forms. They underwent a Premature Aging Protocol (PAP) that took into account the operating conditions typically found in temperature swing adsorption processes. The Si/Al ratio per se did not impact in the crystallinity upon aging, but the presence of a high amount of potassium cations (Si/Al = 1) led to the amorphization of the zeolite structure. The results from XPS and NMR techniques indicate the Al migration from the outer surface to the inner cages occurs upon aging. Chemical analysis by XRF and ICP-OES associated with 27Al NMR analysis reveal that the presence of EFAl is particularly significant in the sample with the largest Si/Al ratio (5) and is correlated to a much larger C deposition upon aging. TG/DTG and TPD-NH3 experiments suggest that acid sites in the zeolite structures act as a double-edged sword, by enhancing water adsorption while also leading to carbon accumulation. CO2 isotherms at 0 ºC reveal the reduction of the microporosity after aging, whereas the Al content is proportional to the water adsorption uptake, particularly at low pressures (below 10 mbar). The material with an intermediate Si/Al ratio and in Na-form (LTAc-SiAl2-Na) combines excellent hydrothermal stability with a high-water affinity and uptake.

Facile synthesis of NaA zeolite supported Co2Fe1 for highly efficient degradation of Acid Orange 7 by activation of peroxymonosulfate.

The development of heterogeneous Co-based catalysts with an effective combination mode of Co/Fe and supporter, a facile synthetic method, and a low treatment cost is an important environment challenge for azo dyes degradation by peroxymonosulfate (PMS) activation. In this study, NaA zeolite supported CoxFey with various molar ratio of Fe/Si and Co/Fe was synthesized by a facile hydrothermal process, and used to activate PMS for Acid Orange 7 (AO7) degradation. NaA zeolite supported Co2Fe1 with the Fe/Si molar ratio of 1:10 showed superior catalytic performance compared with other NaA zeolite supported CoxFey. In a system containing 0.6g/L catalysts, 4mM PMS, pH 5 and T = 30℃, 95.8% AO7 and 79.1% COD conversion could be achieved at 20 and 60min, respectively, and the first order kinetic rate constant reached 0.14795min-1. Moreover, NaA zeolite supported Co2Fe1/PMS system exhibited excellent catalytic effect in a wide pH range of 3-9. Temperature had an obvious effect on AO7 degradation, and the activation energy was 31.36kJ/mol. HCO3- demonstrated an obvious depression on AO7 degradation, while Cl-, SO42- and H2PO4- had a relatively poor impact. Quenching experiments showed that both sulfate radicals ([Formula: see text]) and hydroxyl radicals (·OH) were generated in the PMS reaction system, and the [Formula: see text] was the dominant active radical. During 3 cycles experiments, an acceptable AO7 conversion ratio (91.8%) within 30min arrived, suggesting the good stability of NaA zeolite supported Co2Fe1.

Efficient One‐pot Zeolite Synthesis Protocol from the Metastable *BEA to MTW Topology and Its Impact on the Methanol‐to‐Hydrocarbons Process

AbstractThe inter‐zeolite conversion is a method to convert one meta‐stable zeolite to a thermodynamically stable zeolite. Despite the enormous interest, this method is yet to be popularized or standardized in the zeolite community. Intending to provide more insights into hydrothermal conversions from one zeolite to another, this work developed a novel one‐pot and flexible synthetic protocol to efficiently obtain the meta‐stable *BEA topology and its derived MTW topology by varying the hydrothermal crystallization time. This inter‐zeolite conversion process led to changes in the zeolite framework and modified physicochemical properties during the process. Such a transformation was feasible by forming hierarchical zeolite phases sharing a similar “mtw”‐based common building units, possibly driving such conversion. The structure‐reactivity relationship of four different zeolite materials, synthesized from this one‐pot inter‐zeolite conversion method, was established concerning their performance in the methanol‐to‐hydrocarbon (MTH) process, which has been well supported by operando UV‐vis diffuse reflectance spectroscopic study coupled with online mass spectrometry and solid‐state NMR spectroscopy. As a result, the pathway to synthesize various target zeolites from an identical initial synthesis gel with desired physicochemical properties has been scrutinized.

Hydrothermal synthesis of kaolin-based ZSM-5 zeolite: Effect of synthesis parameters and its application for bioethanol conversion

In petrochemical applications, improving the catalytic activity and stability of Zeolite as a cutting-edge material has gained research interest. Herein, a local South African clay as a source of high silica and alumina with an organic template of tetrapropylammonium bromide (TPABr) was synthesized hydrothermally. The study then examined the effect of crystallization temperature (120–180 °C), crystallization time (24–96 h) and ageing time (0–48 h) on the crystallinity, surface morphology and functional group of the Kaolin-based ZSM-5 Zeolite formed. Characterization results by X-ray diffraction, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the hydrothermal synthesis of the crystalline powder was successful. The XRD revealed the highest intensity at ∑5 with the most intense peaks at 2Ѳ° and a relative crystallinity from 74.6% to 76.66% at the temperature of 180°C and 48 h of ageing and crystallization time of sampled powder. The crystals' growth and pore structure (openings of 5–5.5 Å) was affirmed by the SEM results. Likewise, the BET revealed the surface area (146.15 m2/g), pore volume (0.056 cm3/g) and pore size (59.12 Å). The FTIR spectra vibration within the wavenumber from 545 to 1224 cm−1 also confirmed the sharpness of the beta and pentasil index peaks. Moreso, the bioethanol conversion at the temperature of 180°C over the synthesized ZSM-5 catalyst yielded 2.03% H2, 1.03% CH4, 37.07% C2H4, and 62.4% liquids. This study has demonstrated the synthesized Kaolin-based ZSM-5 Zeolite has the potential for industrial decomposition of ethanol with good catalyst stability.

Morphology-tuned green synthesis of ZIF-67 for non-enzymatic electrochemical detection of glucose

Co-based zeolitic imidazolate framework material (ZIF-67) has both the comprehensive stability of inorganic zeolites and the general advantages of metal-organic frameworks (MOFs), and has devolved as a widely concerned material for electrochemical sensing. ZIF-67 materials with rhombic dodecahedron are synthesized in organic solvent, but morphology-tuned synthesis of ZIF-67 materials can be performed in environment-friendly solvents, usually water. In this work, all ZIF-67 materials were synthesized by three green synthetic methods taking water as a solvent without pollutants. The morphology of ZIF-67 was precisely tuned by changing experimental conditions. ZIF-67 materials were characterized by physicochemical methods and electrochemical techniques, and ZIF-67 materials with different morphologies exhibited different electrocatalytic activities toward the oxidation of glucose. To our amazement, ZIF-67 with an ordered flower-like structures (ZIF-67(W3–25)) has the best performances for non-enzymatic electrochemical detection of glucose, and will be likely to an ideal modifier for a new generation of enzyme-free glucose sensors.

Zeolite fixed cobalt–nickel nanoparticles for coking and sintering resistance in dry reforming of methane

Dry reforming of methane (DRM) displays a crucial role in CO2 fixation, but the current catalysts suffer from deactivation from thermodynamically oriented coking and metal sintering. Herein, we reported a catalyst by fixing the cobalt–nickel nanoparticles within the zeolite crystals (CoNi@zeolite), where the SiOx-O-Mδ+ (M = Ni or Co) linkage enhanced the reduction resistance of Co and Ni species compared with the generally supported catalysts, efficiently hindering the deep dehydrogenation of methane, which is well known as a reaction channel for coke formation. In addition, the rigid and thermally stable zeolite framework stabilized the cobalt–nickel nanoparticles to avoid their sintering during the reaction. As a result, the CoNi@zeolite catalyst exhibited a long reaction lifetime and great regenerability in a test for 980 h with reaction gas flow at 1200 L per unit mass of metal species per hour, outperforming conventionally supported metal catalysts. This work enables a proof-of-the-concept design of durable catalysts by zeolite fixation for the reactions in strongly reductive atmospheres.