Search Results (51)

The esterification of terephthalic acid (PTA) with methanol to dimethyl terephthalate (DMT) was investigated using commercially available zeolite catalysts as the eco-friendly solid acids. Six typical zeolites (ZSM-5-25, ZSM-5-50, ZSM-5-100, ZSM-35, MOR, and β) were systematically evaluated. Among them, β zeolite showed excellent catalytic performance, achieving nearly 100% PTA conversion and 76.1% DMT selectivity under the conditions of 200 °C, of 0.5 MPa N₂ pressure, m(PTA):V(methanol) of 1:40 (g/mL), m(PTA):m(catalyst) of 10:1 over 4 h. The characterization results show that the catalytic efficiency was correlated with acid site strength, specific surface area, and mesoporous structure of the zeolite. After optimization, β zeolite achieved 100% PTA conversion and 94.1% DMT selectivity under the conditions of 200 °C, of 1 MPa N₂ pressure, m(PTA)/V(methanol) of 1:30 (g/mL), m(PTA)/m(catalyst) of 8:1 over 8 h. Moreover, β zeolite exhibited superior stability, maintaining over 92% of its initial activity after five cycles, highlighting its potential for sustainable DMT production. Full article

Size restrictions pose increasing challenges to the acoustic performance of microspeakers in portable devices as the size of such devices, and thus the back volume of microspeakers, continues to shrink. Filling the back volume with porous materials, such as zeolites, has been proved to be an effective strategy for improving acoustic performance. In this work, hierarchically structured ZSM-5 zeolites with abundant mesopores were synthesized via the traditional hydrothermal method by adjusting the SiO₂/Al₂O₃ ratios (SAR), and their pore structures and morphologies were systematically investigated. Their acoustic enhancement performance was evaluated using a commercial microspeaker. Based on their acoustic properties, the influence of pore structure on acoustic performance was further studied. The ZSM-5 zeolite sample with an SAR of 614, which exhibited the maximum mesopore volume, demonstrated exceptional acoustic enhancement performance with a resonance offset of 199.53 Hz and an enhanced sound pressure level of 4.74 dB at 500 Hz. The presence of mesopores significantly facilitates diffusion within the zeolite crystals, enabling air molecules to access more micropores for efficient sorption–desorption processes during diaphragm vibration in microspeakers. Furthermore, supermicropores were found to contribute to improved performance by adsorbing air molecules during diaphragm vibration, complementing the role of micropores. Full article

Zeolite is increasingly recognized for its enhancement of low-frequency acoustic performance in microspeakers. The aging characteristics of zeolite have been regarded as the critical factor for the commercial viability of mobile phones products, but the mechanism remains ambiguous. Here, the low-frequency acoustic performance of hierarchically structured ZSM-5 was investigated through aging with water and acetic acid (AA). It was discovered that water vapor augmented the resonance offset as it enhanced the structure of the zeolite, resulting in a lower water content. The resonance offset of ZSM-5 significantly decreased after the adsorption of AA vapor, as excessive AA was adsorbed through both physical and chemical adsorption, causing partial destruction of supermicropore and mesopores. The performance of ZMS-5 stored with vapor of AA and water mixture did not significantly deteriorate, indicating that water effectively protected the pores of zeolite to prevent excessive adsorption of AA. This was attributed to the fact that water was adsorbed by Brønsted acid sites of ZSM-5 more preferentially than AA, thereby avoiding excessive adsorption of AA. Full article

To address the issue of volatile organic compound (VOC) emissions during crude oil storage and transportation, this study proposes a sandwich-structured zeolite molecular sieve (SMZ) fabricated via a pressing-sintering process integrating ZSM-5 powder and granules. The resulting monolithic zeolite exhibits enhanced mechanical strength and optimized pore architecture. Systematic investigations revealed that sintering at 600 °C with 10% carboxymethyl cellulose (CMC) yielded SMZ with a specific surface area of 349.51 m²/g and pore volume of 0.37 cm³/g. Its hierarchical pore system—micropores (0.495 nm) coupled with mesopores (2–10 nm)—significantly improved adsorption kinetics. Dynamic adsorption tests demonstrated superior performance: SMZ achieved saturation capacities of 127.6 mg/g for propane and 118.2 mg/g for n-butane in liquefied petroleum gas (LPG), with a breakthrough time of 41 min and a 106% increase in adsorption capacity compared to conventional monolithic zeolite (MZ) (90.2 mg/g vs. 43.8 mg/g). Regeneration studies confirmed that combined thermal desorption (250 °C) and nitrogen purging maintained > 95% capacity retention over five cycles, attributed to the high thermal stability of the MFI topology framework (≤600 °C) and crack-resistant ceramic-like interfaces. Additionally, SMZ exhibited exceptional hydrophobicity, with a selectivity coefficient of 20.9 for propane under 60% relative humidity. This work provides theoretical and technical foundations for developing efficient and durable adsorbents for industrial VOC mitigation. Full article

The influence of secondary porosity and the dimensionality of zeolitic structures with 1D and 3D pore systems on the accessibility of cumene to Brønsted acid sites was evaluated in this study. Zeolites Y, ZSM-5, and MOR, obtained through NH4F leaching and basic and acid treatments, were studied. Zeolites Y and ZSM-5 showed a significant increase in specific surface area while maintaining the micropore volume as well as an increase in the concentration of Brønsted acid sites following treatment. Zeolite MOR exhibited an increase in mesopore volume and retained Brønsted acidity. The impact of the treatments on catalytic properties was evaluated through cumene cracking, which yielded high catalytic conversion for the materials. This result is consistent with the goal of the model reaction to characterize Brønsted acid sites, enhance accessibility, and reduce diffusion paths. Full article

The development of hierarchically structured zeolites to mitigate diffusion limitations and improve catalytic performance constitutes a focus of current research. In this study, we present the synthesis of hierarchical disk-shaped MTW zeolite (ZSM-12-P) with shortened channel length using polycation [-C₅H₉N⁺C₁₀H₁₀N⁺C₅H₉-C₃H₆-]_n[Br⁻]_2n (PDIP) as an organic structure-directing agent (OSDA). The ZSM-12-P zeolite forms disk-shaped structures with thicknesses ranging from 140 to 160 nm and exhibits rotational intergrowth. These structures are composed of interconnected nanocrystalline domains that form mesopores accessible from the outer surface, while the microporous channels extend along the thickness direction. In addition, the polycationic OSDA possesses strong interaction with framework and MTW structure-directing ability, enabling the successful synthesis of the Al-rich ZSM-12-P. Owing to its strong acidity and improved diffusion property, the Pt/HZSM-12-P catalyst demonstrates enhanced catalytic n-dodecane hydroisomerization activity and isomer yield. Full article

This paper proposes a method for synthesizing granular ZSM-23 zeolite with a high degree of crystallinity and hierarchical porous structure. This method is based on crystallizing granules composed of powdered ZSM-23 zeolite and a specially prepared amorphous aluminosilicate. It has been shown that these granules have superior mechanical strength compared to granular zeolite-containing materials, which are made from a mixture of ZSM-23 zeolite crystals and Al₂O₃. It has been demonstrated that when 0.5% of Pt granular ZSM-23 zeolite is used, with a high degree of crystallinity and a hierarchical porous structure, it exhibits higher activity and selectivity in the hydroisomerization of n-hexadecane compared to a bifunctional catalyst, which is a mechanical mixture of ZSM-23 zeolite crystals and Al₂O₃, with the metal deposited on the granules. Full article

Fluoride treatment of ZSM-5 zeolite can effectively adjust surface acidity and generate a secondary pore structure. In this study, a series of modified nano-HZSM-5 zeolites were prepared by NH₄F-HF mixed solution treatment and applied to the selective conversion of bioethanol to propylene at 500 °C, atmospheric pressure, and a WHSV of 10 h⁻¹. The results showed that NH₄F-HF modification weakened the surface acidity of nano-HZSM-5 zeolites, thus inhibiting coke formation. Additionally, the mesopores in the nano-HZSM-5 zeolites increased after NH₄F-HF treatment, thereby enhancing the mass transfer rate and improving the coke-resistance ability. The NH₄F-HF mixed solution modification significantly improved the stability of nano-HZSM-5 zeolites in catalyzing bioethanol to propylene and greatly extended the working life of nano-HZSM-5 zeolites. It can be seen from the characterization of the deactivated catalysts that coke deposition and weakening of acidity may be the key factors for catalyst deactivation. Full article

Diffusional limitations associated with zeolite microporous systems can be overcome by developing hierarchical zeolites, i.e., materials with a micro- and mesoporous framework. In this work, Y and ZSM-5 zeolites were modified using a surfactant-mediated hydrothermal alkaline method, with NaOH and cetyltrimethylammonium bromide (CTAB). For Y zeolite, after a mild acidic pretreatment, the effect of the NaOH+CTAB treatment time was investigated. For ZSM-5 zeolite, different concentrations of the base and acid solutions were tested in the two-step pretreatment preceding the hydrothermal treatment. The properties of the materials were studied with different physical–chemical techniques. Hierarchical Y zeolites were characterized by 3.3–5 nm pores formed during the alkaline treatment through the structure reconstruction around the surfactant aggregates. The effectiveness of the NaOH+CTAB treatment was highly dependent on the duration. For intermediate treatment times (6–12 h), both smaller and larger mesopores were also obtained. Hierarchical ZSM-5 zeolites showed a disordered mesoporosity, mainly resulting from the pretreatment rather than from the subsequent hydrothermal treatment. High mesoporosity was obtained when the concentration of the pretreating base solution was sufficiently high and that of the acid one was not excessive. Hierarchical materials can be obtained for both zeolite structures, but the pretreatment and treatment conditions must be tailored to the starting zeolite and the desired type of mesoporosity. Full article

Commercial NH₄-Beta and Na-ZSM-5 zeolites were fluorinated with different amounts of NH₄F and using different procedures (room temperature, conventional refluxing, microwave refluxing). Samples were characterized by XRD, N₂ physisorption, FTIR, ¹H NMR, SEM-EDS, and TGA of adsorbed cyclohexylamine. An increase in the concentration of NH₄F led to fluorinated zeolites with higher surface areas and slightly lower amounts of Brønsted acid sites due to some dealumination. Fluorination by conventional or microwave refluxing at shorter times did not dealuminate ZSM-5, resulting in the formation of higher particle sizes. Ni/fluorinated beta catalysts were more active than Ni/fluorinated ZSM-5 catalysts for the hydrodeoxygenation of guaiacol at 180 °C and 15 bar of H₂ for 1 h due to their higher amount of acid sites. The appropriate proportion of metallic and Brønsted acid centers allowed for the selective obtention of cyclohexane (58%) for the Ni supported on beta fluorinated with NH₄F 0.1 M catalyst. The combination of this fluorinated beta to a Ni/ordered mesoporous carbon catalyst significantly boosted its selectivity to cyclohexane from 0 to 65%. Fluorinated ZSM-5 samples, although having stronger Brønsted acid sites, as observed by ¹H NMR, they had lower amounts, leading to higher selectivity to cyclohexanol when used as catalytic supports. Full article

The low-temperature oxidation of methane gas in coal mine exhaust gas is important for reducing the greenhouse effect and protecting the environment. Unfortunately, the carbon–hydrogen bonds in methane molecules are highly stable, requiring higher reaction temperatures to achieve effective catalytic oxidation. However, metal oxide-based catalysts face the problem of easy sintering and the deactivation of active components at high temperatures, which is an important challenge that catalysts need to overcome in practical applications. In this work, a series of Mn-Co₃O₄ active components were grown in situ on ZSM-5 zeolite with mesoporous pore structures treated with an alkaline solution via a hydrothermal synthesis method. Due to the presence of polyethylene glycol as a structure-directing agent, manganese can be uniformly doped into the Co₃O₄ lattice. The large specific surface area of ZSM-5 zeolite allows the active component Mn-Co₃O₄ to be uniformly dispersed, effectively preventing the sintering and growth of active component particles during the catalytic reaction process. It is worth mentioning that the Mn-Co₃O₄/meso-ZSM-5-6.67 catalyst has a methane conversion rate of up to 90% at a space velocity of 36,000 mL·g⁻¹·h⁻¹ and a reaction temperature of 363 °C. This is mainly due to the mesoporous ZSM-5 carrier with a high specific surface area, which is conducive to the adsorption and mass transfer of reaction molecules. The active component has an abundance of oxygen vacancies, which is conducive to the activation of reaction molecules and enhances its catalytic activity, which is even higher than that of noble metal-based catalysts. The new ideas for the preparation of metal oxide-based low-temperature methane oxidation catalysts proposed in this work are expected to provide new solutions for low-temperature methane oxidation reactions and promote technological progress in related fields. Full article

Here, we report the results of our ¹H nuclear magnetic resonance study of the dynamics of water molecules confined in zeolites (mordenite and ZSM-5 structures) with hierarchical porosity (micropores in zeolite lamella and mesopores formed by amorphous SiO₂ in the inter-lamellar space). ¹H nuclear magnetic resonance (NMR) spectra show that water experiences complex behavior within the temperature range from 173 to 298 K. The temperature dependence of ¹H spin-lattice relaxation evidences the presence of three processes with different activation energies: freezing (about 30 kJ/mol), fast rotation (about 10 kJ/mol), and translational motion of water molecules (23.6 and 26.0 kJ/mol for pillared mordenite and ZSM-5, respectively). For translational motion, the activation energy is markedly lower than for water in mesoporous silica or zeolites with similar mesopore size but with disordered secondary porosity. This indicates that the process of water diffusion in zeolites with hierarchical porosity is governed not only by the presence of mesopores, but also by the mutual arrangement of meso- and micropores. The translational motion of water molecules is determined mainly by zeolite micropores. Full article

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. Full article

The dehydroaromatization of methane (MDA) is of great interest as a promising process for processing natural and associated petroleum gases, the main component of which is methane. The rapid loss of catalyst activity because of coke formation hinders the introduction of the DHA methane process into the industry. Therefore, the aim of this research was to find ways to improve Mo/ZSM-5 catalysts for MDA. The paper presents the results of the synthesis of high-silica zeolites of the ZSM-5 type with microporous and micro–mesoporous structures, the preparation of Mo/ZSM-5 catalysts based on them, and the study of the physicochemical and catalytic properties of the obtained samples during the non-oxidative conversion of methane into aromatic hydrocarbons. Zeolite catalysts were investigated using IR spectroscopy, X-ray diffraction, TPD-NH₃, SEM, HR-TEM, and N₂ adsorption. It was found that the addition of carbon black in the stage of the synthesis of zeolite type ZSM-5 did not lead to structural changes, and the obtained samples had a crystallinity degree equal to 100%. The creation of the micro–mesoporous structure in Mo/ZSM-5 catalysts led to an increase in their activity and stability in the process of methane dehydroaromatization. The highest conversion of methane was observed on a 4.0%Mo/ZSM-5 catalyst prepared based on zeolite synthesized using 1.0% carbon black and was 13.0% after 20 min of reaction, while the benzene yield reached 7.0%. It was shown using HR-TEM that a more uniform distribution of the active metal component was observed in a zeolite catalyst with a micro–mesoporous structure than in a microporous zeolite. Full article

In this study, a novel dispersive micro-solid phase extraction (D-μSPE) technique with H-ZSM-5 zeolite as an adsorbent was developed for the determination of 21 trace pesticides in tea beverages. The adsorption and desorption of H-ZSM-5 zeolites were investigated based on structural characteristics and adsorption properties similar to those of H-beta zeolites. In combination with the properties of the adsorbates, it was explained that the adsorption reaction occurred on the microporous surface and mesopores of H-ZSM-5. Based on optimal parameters, the beverage samples were extracted by 50 mg of zeolite within 1 min. The zeolite was eluted with 2 mL of an acetonitrile-water mixture after separation, and the eluent was filtered prior to HPLC-MS/MS analysis. The D-μSPE protocol demonstrated acceptable accuracy and precision, with recoveries between 62.1% and 106.6% and relative standard deviations of 1.4% to 12.6%, as validated by analytical reliability. The correlation coefficient in the linear range of 0.2–50 ng·mL⁻¹ was greater than 0.98, with limits of detection of 0.05–0.1 ng·mL⁻¹ and limits of quantification of 0.1–0.2 ng·mL⁻¹. The matrix effects ranged from 76.2% to 112.7%. The results indicate that the novel D-μSPE technique based on H-ZSM-5 is a rapid, simple, green and economical method for the determination of pesticide residues in tea beverages. The proposed method achieved simultaneously low adsorbent dosage, 20-fold enrichment factor, rapid pre-concentration in 12 min, minimal organic wastes, and effective reduction of matrix interference. Full article