Search Results (44)

The siliceous precursor was hydrolyzed from tetraethylorthosilicate (TEOS) under acidic conditions, followed by the addition of sodium aluminate and sodium hydroxide. Y zeolite was subsequently obtained through hydrothermal crystallization under alkaline conditions. Key synthesis parameters, including reactant molar ratios, crystallization temperature, and time, were systematically varied to optimize the synthesis conditions. The synthesized products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption analysis, and inductively coupled plasma (ICP) elemental analysis. Well-crystallized Y zeolite with a silica-alumina ratio (SAR) of 5.55 was successfully synthesized via TEOS hydrolysis catalyzed by sulfuric acid at a low crystallization temperature of 85 °C. The catalytic performance of benzyl phenyl ether, a lignin model compound, over NiY catalyst was evaluated in a high-pressure reactor. The results indicate that the catalytic efficiency of Y zeolite synthesized using TEOS as the silicon source under acidic hydrolysis conditions is significantly superior to Y zeolite prepared using alkaline silica sol as the silicon source. Full article

In this work, the facile reflux method was used as a crystallization procedure for zeolite NaY synthesis. The zeolite mixture was aged for 7 days and then refluxed for crystallization at 100 °C for 12 h. The synthesized zeolite NaY was impregnated with 10, 20 and 30 wt%Ni solution to use as a catalyst for CO₂ methanation. The 30 wt% of Ni on the zeolite NaY catalyst showed the highest CO₂ methanation catalytic activity, with almost 100% CH₄ selectivity. This can be explained by an appropriate H₂ and CO₂ adsorption amount on a catalyst surface being able to facilitate the surface reaction between them and further react to form products. The oxidation state of Ni and the stability of the catalyst were monitored by time-resolved X-ray absorption spectroscopy. The oxidation state of Ni²⁺ was reduced during the catalyst reduction prior to the CO₂ methanation and it was completely reduced to Ni° at 600 °C. During CO₂ methanation, Ni° remained unchanged. In addition, the stability test of the catalyst was conducted by exposing the catalyst to a fluctuating condition (CO₂ + H₂ and only CO₂). The oxidation state of Ni° remained unchanged under the fluctuating condition. This indicated that the Ni/zeolite catalyst has high stability, which can be attributed to an appropriate binding strength between Ni and the zeolite support. Full article

Zeolite NaP1 was found to display the highest affinity for CO₂ in preliminary modifications of coal fly ash-derived zeolites (4A, Y, NaP1 and X) by four amines (1,3-diaminopropane, N,N,N′,N′-tetramethylethylenediamine, Tris(2-aminoethyl)amine and ethylenediamine). In the second step, different fatty acid loaded NaP1 samples were prepared using palmitic, oleic and lauric acids. CO₂ and H₂O thermal programmed desorption (TPD) revealed changes in intrinsic basicity and hydrophilic character, expressed in terms of CO₂ and H₂O retention capacity (CRC and WRC, respectively). Infrared spectroscopy (IR), N₂ adsorption-desorption isotherms and scanning electron microscopy allowed for correlating these changes with the type of interactions between the incorporated species and the zeolite surface. The highest CRC values and the lowest CO₂ desorption temperatures were registered for NaP1 with the optimum content in palmitic acid (PA) and were explained in terms of the shading effect of surface acidity by the rise of basic Na⁺-palmitate salt upon cation exchange. The amine/fatty acid combination was found to paradoxically mitigate this beneficial effect of PA incorporation. These results are of great interest because they demonstrate that fatty acid incorporation is an interesting strategy for reversible CO₂ capture. Full article

Ti-aluminosilicate gels were used as supports for the immobilization of Fe, Co, and Ni oxides (5%) by impregnation and synthesis of efficient photocatalysts for the degradation of β-lactam antibiotics from water. Titanium oxide (1 and 2%) was incorporated into the zeolite network by modifying the gel during the zeolitization process. The formation of the zeolite Y structure and its microporous structure were evidenced by X-ray diffraction and N₂ physisorption. The structure, composition, reduction, and optical properties were studied by X-ray diffraction, H₂-TPR, XPS, Raman, photoluminescence, and UV–Vis spectroscopy. The obtained results indicated a zeolite Y structure for all photocatalysts with tetracoordinated Ti⁴⁺ sites. The second transitional metals supported by the post-synthesis method were obtained in various forms, such as oxides and/or in the metallic state. A red shift of the absorption edge was observed in the UV–Vis spectra of photocatalysts upon the addition of Fe, Co, or Ni species. The photocatalytic performances were evaluated for the degradation of cefuroxime in water under visible light irradiation. The best results were obtained for iron-immobilized photocatalysts. Scavenger experiments explained the photocatalytic results and their mechanisms. A different contribution of the active species to the photocatalytic reactions was evidenced. Full article

Hierarchical ZSM5 and Y zeolites were prepared through a surfactant-mediated strategy with NH₄OH changing the duration of the treatment and the amount of CTAB surfactant and taking as reference multiples of the critical micellar concentration (CMC). The materials were characterized using powder X-ray diffraction, N₂ adsorption isotherms at −196 °C, and SEM and TEM microscopy. The catalytic performance was evaluated in Friedel–Crafts acylation of furan with acetic anhydride at 80 °C. The alkaline surfactant-mediated treatment had different effects on the two zeolites. For ZSM5, the CTAB molecular aggregates can hardly diffuse inside the medium-size pores, leading mainly to intercrystalline mesoporosity and increased external surface area, with no positive catalytic impact. On the other hand, for large-pore Y zeolite, the CTAB molecular aggregates can easily diffuse and promote the rearrangement of crystal units around micelles, causing the enlargement of the pores, i.e., intracrystalline porosity. The optimized Y-based sample, treated for 12 h with a CTAB amount 32 times the CMC, shows an increase in product yield and rate constant that was not observed when a higher amount of surfactant was added. The reuse of spent catalysts upon thermal treatment at 400 °C shows a regeneration efficiency around 90%, showing good potentialities for the modified catalysts. Full article

Extensive research has been conducted on platinum nanoparticles or clusters supported on zeolite for various catalytic applications, primarily due to the well-defined structure contained within the pore. The preparation and characterization of these particles have been thoroughly examined using advanced techniques such as X-ray absorption fine structures (XAFSs), both in situ and ex situ. In this study, we employed the Wavelet method to analyze the structure of platinum nanoparticles encapsulated within the supercage of a Y zeolite, where XAFS data were collected over a temperature range of 100 K to 423 K, both with and without hydrogen. The adsorption of hydrogen caused a relaxation in the structure of the platinum nanoparticles, thus leading to a decrease in the Pt–Pt distance and resulting in a lower Debye–Waller factor compared to bare nanoparticles. This structural change induced by hydrogen chemisorption aligns with the findings of the density functional theory (DFT) calculations for Pt₁₃ nanoparticles located in the supercage. The relaxation of the structure results in charge redistribution, thereby ultimately generating atomic hydrogen with a partial negative charge, which is crucial for catalytic processes. Full article

Zeolite Y samples with microporous and hierarchical structures containing Ti–Ni and Ti–Co oxides were obtained as active photocatalysts. Different Ti amounts (5, 10% TiO₂) were supported, followed by the loading of Ni or Co oxides (5%). X-ray diffraction evidenced the presence of TiO₂ as an anatase. N₂ adsorption–desorption results showed type IV isotherms for hierarchical zeolite Y samples, and a combination of type IV and I isotherms for zeolite Y samples. UV–Vis diffuse reflectance spectra showed a shift in the absorption band to visible with increasing Ti loading and especially after Co and Ni addition. A significant effect of the support was evidenced for Ti and its interaction with Co/Ni species. The zeolite Y support stabilized Ti in the 4+ oxidation state while hierarchical zeolite Y support favored the formation of Ti³⁺ species, Ni⁰ and Ni²⁺ and the oxidation of Co to 3+ oxidation state. Photocatalytic activity, under UV and visible light irradiation, was evaluated by the degradation of amoxicillin, used as a model test. The photocatalytic mechanism was investigated using ethanol, p-benzoquinone and KI as ·OH and ·O₂⁻ radicals and hole (h⁺) scavengers. The best results were obtained for the immobilized Ni-Ti species on the hierarchical zeolite Y support. Full article

The single-component adsorption of CO₂, CO, N₂, and H₂ at 25 and 35 °C was studied using microporous faujasite-framework zeolites (NaY and NaX), activated carbons (GCN and MSP), and metal–organic frameworks (A100 and Z1200) as starting points for the separation of CO₂ from syngases produced by gasifying biomass-based solid wastes. The indicated adsorption isotherms and uptake of the adsorbates strongly depended on the adsorbates themselves as well as on the adsorbents because of significant differences in the surface features, such as surface nonuniformity, and in the molecular properties. The selectivity of CO₂ to the other gases also varied with the adsorbents due to the distinctive energetic characteristics. The surfaces of the zeolites were the most energetically heterogeneous ones, yielding higher CO₂ uptake at low pressures, while the two activated carbons and A100 had moderate surface heterogeneities, and MSP showed the highest CO₂ uptake at high pressures, such as 6 bar, at which the micropore volume and surface area are important. Z1200, which has highly homogeneous surfaces and no high-affinity-binding sites, exhibited the lowest CO₂ adsorption capacity regardless of equilibrated pressure. The surface nonuniformities of the six sorbents were consistent with the calculated isosteric heats of CO₂ adsorption. CO₂ could be reversibly adsorbed on NaY and MSP but not on GCN, with some metal impurities, although all these adsorbents showed a fully reversible process for CO adsorption. The estimated working capacity for CO₂ adsorption at 25 °C was 0.78–6.50 mmol/g, depending on the sorbents used. The highest value was disclosed for MSP, the surface energetic heterogeneity of which was between that of zeolites and Z1200. Such a high working capacity bodes well for use in our later applications. Full article

Zeolites in powder form have the potential to agglomerate, lowering access to active sites. Furthermore, a suspension of fine zeolite powder in liquid media is difficult to separate. Such drawbacks could be improved by dispersing zeolite crystals on support materials. This work demonstrates the dispersion of zeolite NaY crystals on bamboo wood by mixing the wood with zeolite gel before hydrothermal treatment. The syntheses were performed with acid-refluxed and non–refluxed wood. The phase of zeolites, particle distribution and morphology, zeolite content in the wood, and zeolite–wood interaction were investigated using X-ray diffraction, X-ray tomography, scanning electron microscopy, thermogravimetric analysis, nitrogen sorption analysis, and X-ray photoelectron spectroscopy. Higher zeolite content and better particle dispersion were obtained in the synthesis with the acid–refluxed wood. The composite of NaY on the acid-refluxed wood was demonstrated to be an effective adsorbent for Ni(II) ions in aqueous solutions, providing a higher adsorbed amount of Ni(II) per weight of NaY. Full article

The present work reports the synthesis of efficient Ti–Au/zeolite Y photocatalysts by different processing of aluminosilicate gel and studies the effect of titania content on the structural, morphological, textural, and optical properties of the materials. The best characteristics of zeolite Y were obtained by aging the synthesis gel in static conditions and mixing the precursors under magnetic stirring. Titania (5, 10, 20%) and gold (1%) species were incorporated in zeolite Y support by the post-synthesis method. The samples were characterized by X-ray diffraction, N₂-physisorption, SEM, Raman, UV–Vis and photoluminescence spectroscopy, XPS, H₂-TPR, and CO₂-TPD. The photocatalyst with the lowest TiO₂ loading shows only metallic Au on the outermost surface layer, while a higher content favors the formation of additional species such as: cluster type Au, Au¹⁺, and Au³⁺. A high TiO₂ content contributes to increasing the lifetime of photogenerated charge careers, and the adsorption capacity of the pollutant. Therefore, an increase in the photocatalytic performances (evaluated in degradation of amoxicillin in water under UV and visible light) was evidenced with the titania content. The effect is more significant in visible light due to the surface plasmon resonance (SPR) effect of gold interacting with the supported titania. Full article

This work is focused on the application of Cu-containing zeolites as potential environmental sensors for monitoring carbon monoxide. A number of commercial zeolites with different structural properties (NaX, NaY, MOR, FER, BEA and ZSM-5) were modified using CuSO₄, Cu(NO₃)₂ and Cu(OAc)₂ solutions as copper sources to prepare Cu⁺-containing zeolites, since Cu⁺ forms stable complexes with CO at room temperature that can be monitored by infrared spectroscopy. Zeolite impregnation with Cu(NO₃)₂ resulted in the highest total Cu-loadings, while the Cu(OAc)₂-treated samples had the highest Cu⁺/Cu_total ratio. Cu(NO₃)₂-impregnated MOR, which displayed the highest concentration of Cu⁺, was subjected to a number of tests to evaluate its performance as a potential CO sensor. The working temperature and concentration ranges of the sensor were determined to be from 20 to 300 °C and from 10 to 10,000 ppm, respectively. The stepwise CO desorption experiments indicated that the sensor can be regenerated at 400 °C if required. Additional analyses under realistic flow conditions demonstrated that for hydrophilic zeolites, the co-adsorption of water can compromise the sensor’s performance. Therefore, a hydrophobic Sn-BEA was utilised as a parent material for the preparation of an impregnated Cu-Sn-BEA zeolite, which exhibited superior resistance to interfering water while maintaining its sensing properties. Overall, the prepared Cu-modified zeolites showed promising potential as environmental CO sensors, displaying high sensitivity and selectivity under representative testing conditions. Full article

Hierarchical zeolites are aluminosilicates with a crystal structure, which next to the micropores possess secondary porosity in the range of mesopores and/or small macropores. Due to their ordered structure and additional secondary porosity, they have aroused great interest among scientists in recent years. Therefore, the present work concerns the synthesis and characterization of hierarchical zeolites with secondary mesoporosity, based on commercial zeolites such as MFI (ZSM-5), BEA (β) and FAU (Y), and modified with polysaccharides such as inulin, hyaluronic acid, and heparin. All materials were characterized by various analytical techniques and applied as a platform for delivery of selected drug molecules. On the basis of X-ray diffraction (presence of reflections in the 2θ angle range of 1.5–2.5°) and low-temperature nitrogen sorption isotherms (mixture of isotherms of I and IV type) additional secondary porosity was found in the mesopore range. Additional tests were also conducted to determine the possibility of loading selected molecules with biological activity into the aforementioned materials and then releasing them in the therapeutic process. Molecules with different therapeutic options were selected for testing, namely ibuprofen, curcumin, and ferulic acid with anti-inflammatory, potentially anticancer, antioxidant, and skin discoloration activities, respectively. Preliminary studies have confirmed the possibility of using hierarchical zeolites as potential carriers for bioactive molecules, as the loading percentage of active substances ranged from 39–79% and cumulative release for ibuprofen reached almost 100% after 8 h of testing. Full article

Cobalt and lithium are critical metals because of its shortage, difficulty of extraction and huge economic impact due to their market value. The purpose of this work is to study their selective removal from aqueous solutions in different conditions using two commercial FAU zeolites as adsorbent materials. These solids were characterized by XRD, XRF and BET analysis, to follow up of their FAU structure integrity, their Si/Al ratio, and their specific surface area evolutions through their preparation process. The kinetic study indicates that using both zeolites with a dosage of 5 g/L a 100% cobalt removal from aqueous solutions is achievable, while lithium removal is kept around 30% (separation factor of 3.33). This selectivity is important as these two metals frequently appear together in leaching solutions form, for example, ion-Li batteries. In relation to the adsorption equilibrium, cobalt adsorption presents a finite adsorption capacity while this behavior is not observed in lithium adsorption. For this reason, Langmuir model is the most adequate to represent cobalt adsorption, while lithium adsorption is better represented by Freundlich model. Full article

The organization of microporous space in zeolites is discussed. A new step-by-step model is proposed that explains the principles of organizing the hierarchy of microporous space at the stage of assembling zeolites from elements of minimal size: a primary building unit, secondary building units, tertiary building units or building polyhedra, a sodalite cage, and a supercage. To illustrate the stepwise hierarchical porous structure of nanomaterials, the following zeolites with small and large micropores have been selected as the model objects: sodalite (SOD, the maximum diameter of a sphere that can enter the pores is 0.3 nm) and zeolites of type A (LTA, the maximum diameter of a sphere that can enter the pores is 0.41 nm), type X, Y (FAU, the maximum diameter of a sphere that can enter the pores is 0.75 nm), and type BETA (the maximum diameter of a sphere that can enter the pores is 0.67 nm). Two-dimensional and three-dimensional modeling in 3Ds Max software was used. We believe that such an approach will be useful for developing ways to create complex zeolite compositions for specific applications, such as catalysis, where the geometry of the pores determines the size of the molecules entering the voids and computer modeling can play an important predictive role. This work takes a look at specific aspects of using the heat desorption method to study mesoporous materials with a BETA zeolite as an example and presents the results of experimental research into the characteristics of the porous structure of hierarchically structured zeolite materials (specific surface area 180–380 m²/g, external surface area 120–200 m²/g, micropore volume 0.001–0.1 mL/g). Full article

Zeolite Y and Ti-containing zeolite Y (1%, 2% and 5% TiO₂) were synthesized by a hydrothermal seed-assisted method. In order to evidence the evolution of morphology, structure, and fractal dimensions during the zeolitization process at certain time intervals, a small volume from the reaction medium was isolated and frozen by lyophilization. The obtained samples were characterized by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). The fractal dimension values of the isolated samples, calculated from SAXS data, evidenced a transition from small particles with a smooth surface (2.021) to compact structures represented by zeolite crystallites with rough surfaces (2.498) and specific organization for zeolite Y. The formation of new structures during hydrothermal treatment, the increase in crystallite size and roughness due to the continuous growth were suggested by variation of fractal dimensions values, SEM microscopy images and X-ray diffractograms. The incorporation of titanium in low concentration into the zeolite Y framework led to the obtaining of low fractal dimensions of 2.034–2.275 (smooth surfaces and compact structures). On the other hand, higher titanium concentration (2%) led to an increase in fractal dimensions indicating structures with rougher surfaces and well-defined self-similarity properties. A mechanism for zeolite synthesis was proposed by correlation of the results obtained through morphological, structural, and fractal analysis. Full article