Zeolite Surface Research Articles

OBTAINING NEW MATERIALS BASED ON A COMBINATION OF SYNTHETIC ZEOLITES AND SILVER NANOPARTICLES

Nano silver has long been known as a highly effective disinfectant, capable of limiting the growth and eliminating many types of mold and bacteria. Nano silver can be synthesized by many different methods, depending on the purpose and requirements of use. Nano silver can be dispersed in solution or carried onto carriers for different applications. However, in solution, silver nanoparticles often tend to bind together, reducing antibacterial activity. In order to promote the antibacterial ability of nano silver and be able to recover and reuse many times, as well as to be able to disperse well into different materials, nano silver is often put on the carriers. In this study, nanosilver was synthesized on the surface of a zeolite by simple methods such as chemical reduction with NaBH4, N2H4 or thermal reduction at 350 °C. Ag+ ions are adsorbed onto 4A zeolite by ion exchange mechanism, then reduced by different methods. The materials were morphologically analyzed by XRD, SEM, EDX methods. Results showed that the method of reducing Ag+ to Ag0 on zeolite surface by chemical agent produce more evenly distributed silver nano-sized particles than the thermal reduction method. The silver content on the zeolite surface of the hydrazine reduction method is about 3 times higher than that of the sodium borohydride reduction method. The highest content of silver nanocarrying to zeolite. Zeolite bearing nano silver has the ability to disinfect against E.Coli with a concentration of ≥ 5 mg/ml. The Ag02/Z sample reducing Ag+ to Ag0 by Hydrazin has the best antibacterial ability against E.coli compared with the remaining samples when the diameter of the sterile ring at the concentration of 20 mg/ml is 9 mm. For citation: Xuan Minh Vu, Thi Lan Pham, Thi My Hanh Le, Thi Thu Hoai Pham, Chi Mai Nguyen, Dai Lam Tran Obtaining new materials based on a combination of synthetic zeolites and silver nanoparticles. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 59-65. DOI: 10.6060/ivkkt.20236603.6722.

Adsorption Properties, Catalytic Activity, and Thermal Stability of β-Galactosidase on the Surface of Zeolites

Adsorption Properties, Catalytic Activity, and Thermal Stability of β-Galactosidase on the Surface of Zeolites

Architecture of copper sulfide heterojunction and sodalite zeolite for synergistically improving catalytic effectiveness toward methanol oxidation

CuxS derivatives perform high activity in MOR (methanol oxidation reaction) through the co-operation of Cu and S. In order to further improve their performance, the composition and structure are regulated through the co-growth process of copper sulfide heterojunction and SOD (sodalite code) zeolite framework. Under the hydrothermal condition, the introduced Cu0 and Cu+ ions are clustered on the zeolitic surface and inner cages. The S2- anions are selectively located at the zeolite cage to balance the framework charge arisen from the incorporation of Cu+. In the electrochemical process, the optimized Cu2S/SOD zeolite electrode reveals an extra high efficiency of 8847 A g−1 at an extra low overpotential of 0.374 V with an excellent resistance to catalyst poisoning in high concentration of methanol. This work opens up a new method for the design and industrial application of non-precious metal electrocatalysts with high energy density based on porous zeolite materials.

Moderate pressure boosts the aromatization activity of HZSM-5 zeolite during catalytic pyrolysis of lignocellulosic materials

Lignocellulose pyrolysis has been deeply investigated in the past years as a potential route for the production of advanced biofuels and biochemicals from residues and wastes. However, the effect of pressure has rarely been addressed in catalytic pyrolysis processes. Accordingly, the current work reports a comprehensive study on the pressure influence during the catalytic pyrolysis of different lignocellulosic materials (oak wood, cellulose, hemicellulose, and lignin) using nanocrystalline HZSM-5 zeolite as a catalyst and a downflow fixed-bed reactor. In thermal pyrolysis tests, pressure increase affects negatively the bio-oil* (organic components in the liquid products) since it reduces its yield in favor of the production of char and gases. However, in the case of the catalytic pyrolysis tests, working under moderate pressure (10 bar) has very positive effects on bio-oil upgrading, minimizing its oxygen concentration (< 10 wt.%) and sharply increasing the carbon yield of aromatic hydrocarbons, while the undesirable coke deposited on the catalyst surface can be even reduced. This finding denotes the occurrence of a remarkable synergistic effect between the pyrolysis pressure and the catalyst loading. These outstanding results are attributed to a more efficient activity of the zeolite under mild pressurization since both oxygenated species and light olefins are more strongly adsorbed over the catalyst surface, facilitating their subsequent transformation into aromatic hydrocarbons. The sharp enhancement of the deoxygenation and aromatization activity does not involve higher coke deposition over the zeolite surface, thus attenuating one of the major limitations of the lignocellulose catalytic pyrolysis process.

Runoff regulation and nitrogen and phosphorus removal performance of a bioretention substrate with HDTMA-modified zeolite

As a commonly used material in bioretention substrates, natural zeolite (NZ) provides decent adsorption capacity for cation pollutants and heavy metals, but limited ability to remove anion pollutants. Hexadecyltrimethylammonium bromide (HDTMA)-modified zeolite (MZ) was used as the bioretention substrate material. The performance of the media including runoff reduction, nitrate nitrogen (NO3−-N) removal, ammonium nitrogen (NH4+-N) removal, and total phosphorus (TP) removal was assessed by the column experiment. The effects of different levels of modification, ratio of zeolite in the substrate, and rainfall intensity on media performance were investigated. The results indicate that HDTMA-modified zeolite significantly improves the NO3−-N (up to 38.2 times of NZ) and TP (up to17.5 times of NZ) removal rate of media and slightly increases the NH4+-N (up to 1.5 times of NZ) purification performance of the substrate. Compared with the media with NZ, decline on both runoff volume reduction (maximum decline up to 32.9%) and flow rate reduction (maximum decline up to 29.9%) of the media with MZ were observed. Based on multiple regression analysis, quantitative relationship models between influencing factors and response variables were established (R2 &amp;gt; 0.793), the level of the effect of influencing factors on response variables was investigated, and the interactions between influencing factors were explored. The main effect analysis found that the degree of modification affects NO3−-N and TP removal rate of the substrate the most, and when the amount of HDTMA molecules loaded on the zeolite surface exceeds 0.09meq/g, the modification can no longer improve NO3−-N removal efficiency.

Designing molybdenum disulfide/nickel silicide@sodalite zeolite structure as a high performance core-shell catalyst for methanol oxidation

The design and synthesis of novel electrode catalysts is an applicable strategy to improve the performance of direct methanol fuel cells (DMFCs). The catalyst is composed of molybdenum disulfide as the shell and nickel silicide-doped sodalite (MoS2/NiSi@SOD) as the core. A series of characterization results indicate that NiSi is highly dispersed in the nanosized SOD cage on the surface of the SOD zeolite at the crystal faces of (011), (102), and (201). A thin conductive protective cover is formed by MoS2 on the surface of the zeolite. By the cyclic voltammetry (CV), the catalyst performs a maximum current density of 46.9 mA cm−2 (1250.1 A gNi−1) with 10 M methanol while no remarkable catalyst poisoning and catalyst deactivation are observed. It is revealed that MoS2/NiSi@SOD under high catalysis activity protects the Ni from the drain in the alkaline electrolyte, leading to a broad application prospect as a noble-metals-free DMFC catalyst.

Study on electrical double layer nanostructure on zeolitic materials’ surface in the presence of impurities of different nature

The aim of the research was to compare the adsorption mechanisms of heavy metal ions (Pb(II) and Zn(II)), as well as organic substances [diclofenac molecules and pol(acrylic acid) macromolecules on the surfaces of Na-X and Na-P1 synthetic zeolites as well their Na-X© and Na-P1© carbon composites]. The single and mixed adsorbate systems were considered. The more probable structures of the formed adsorption layers were proposed based on the results of the solid surface charge density and zeta potential experiments. The great applicability of the analysis of the parameters characterizing the electrical double layer in determination of the binding mechanism of simple inorganic ions and more complex organic molecules on the surface of the examined solids from the one- and two-component solutions was proved. Moreover, the changes of the surface and electrokinetic factors after the addition of the organic molecules enable specification of drug molecule orientation as well as the polymeric chain conformation at the solid/liquid interface.

Removal of H2S from simulated blast furnace gas by adsorption over metal-modified 13X zeolite

With the promulgation of new regulations, it’s of great significance to desulfurization from blast furnace gas (BFG) to meet the clean production of iron making industry. Among different desulfurization technologies, zeolite-based sorbents are extensively studied due to the easy operation, low operating cost, and long service life. In this research, the 13X zeolite was selected, and it was ion-exchanged by different metal elements (Cu, Zn, Co, Mn) to prepared a series of sorbents. A fixed bed was used to evaluate their desulfurization behavior, and the XRD, SEM, ICP-OES, XPS, N2 adsorption, and CO2-TPD were carried out to characterize the physical and chemical properties of sorbents. The effects of water vapor content and desulfurization temperature on the removal of H2S were investigated. The regeneration performance of sorbent was also explored. The results showed that the Cu25X-Ex sorbent has the highest breakthrough sulfur capacity of 7.71 g S/100 g sorbent in dry simulated BFG. The breakthrough sulfur capacity of Cu25X-Ex was 4.52 g S/100 g sorbent when the water vapor content is 5 %. The CO2-TPD results showed that the basic sites were favorable for the adsorption of H2S on the surface of zeolite. The XPS results illustrate that the forms of S adsorbed on Cu25X-Ex sorbent were CuS, CuS2O3, and CuSO4, so it is suggested that the reaction between adsorbed H2S with the metal cations in sorbent occurred subsequently. The research indicated that Cu25X-Ex sorbent has potential applicability in the desulfurization of blast furnace gas.

Colloidal Stabilization of Submicron-Sized Zeolite NaA in Ethanol-Water Mixtures for Nanostructuring into Thin Films and Nanofibers.

Despite the growing use of organic or mixed solvents in zeolite processing, most studies focus only on aqueous suspension systems. We investigated the colloidal characteristics of submicron-sized zeolite NaA in mixed ethanol-water solvents. The effects of the mixing ratio of solvents and various additives on the dispersion of the zeolite powders were studied. The zeolite NaA particles were destabilized in solvent mixtures at a high ethanol-to-water ratio, a reduction in the zeta potential was observed, and the destabilization was rationalized by the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory. An improved stabilization of the zeolite NaA suspensions was achieved in ethanol-rich solvent mixtures using nonionic low molecular weight organic additives, but not with their ionic counterparts such as anionic, cationic surfactants or inorganic acids or bases. Polyethylene glycol (PEG)-400 was found to be a good dispersant for the submicron-sized zeolite NaA particles in the ethanol-water mixtures, which was attributed to its interaction with the zeolite surface, leading to an increased zeta potential. The PEG-stabilized zeolite suspensions led to low suspension viscosities as well as uniform and consistent spin-coated films.

Enhanced catalytic performance of CuCr/ZSM-5 catalyst by chemical vapour deposition for trichloroethylene oxidation

ABSTRACT The CuCr mixed oxides catalysts supported on ZSM-5 zeolite (CuCr/ZSM-5) were synthesized via metal organic chemical vapour deposition (MOCVD) method for catalytic oxidation of trichloroethylene (TCE). SEM, XRD, BET, H2-TPR, NH3-TPD and XPS were tested. The active components were dispersed uniformly over the surface of ZSM-5 zeolite. The catalytic experimental results exhibited that the CuCr/ZSM-5 exhibited the best catalytic performance for TCE oxidation with 90% of TCE at 338°C and the concentration of C2Cl4 decreased compared with Cu/ZSM-5 and Cr/ZSM-5. The possible reason is that CuCr/ZSM-5 has superior reducibility, higher Cu2+ surface concentration as well as more surface oxygen.

Synthesis and Acidity Study of Mixed MFI-MORD Type Zeolite

Zeolites of various nature are widely used in the chemical industry, the fuel and energy sector of the economy as sorbents, catalysts and materials for the creation of inorganic membranes for various purposes. At the same time, it is possible to change the acid properties of the surface of zeolites both by varying the ratio of silicon to aluminum or silicon to phosphorus, and by joint synthesis of zeolites of various types with different acidic properties. The presented article provides a method for the sequential production of a zeolite of a mixed structure type MFI and mordenite. Synthesis of the original MFI type zeolite was carried out using seed grains by the hydrothermal method for 72 hours, followed by washing and drying of the zeolite. To obtain a layer of mordenite on the surface of the MFI type zeolite, the initial zeolite was pretreated with alkali and then treated with n-butylamine. In this way, nine samples of zeolite with different acidic surface properties were obtained. Determination of the acidic properties of the surface was carried out by the method of ammonia chemisorption followed by its desorption from the surface of the zeolite. For this purpose, the test sample was loaded into a quartz cuvette, purged with argon at a temperature of 800°С, after which the temperature dropped to 150°С, and the surface of the zeolite was treated with ammonia. Subsequently, the test sample was heated up to 800°С with registration of desorption curves. The amount of adsorbed ammonia was carried out according to previously prepared calibration curves. The synthesized samples of zeolites had different acidity from 0.48 to 0.72 mmol(NH3)/g(sample). In this case, the total acidity of the samples correlated with the ratio of silicon to aluminum in the zeolite samples. Also, depending on the ratio of the MFI and mordenite structures in the zeolite sample, it is possible to vary not only the number, but also the strength of the formed acid sites. So, an increase in the content of mordenite contributes to an increase in the strength of acid centers. The developed method for the synthesis of mixed structure zeolites of the MFI type mordenite made it possible to control the surface acidity of the synthesized samples.

Catalytic Properties Study of Mixed MFI-MORD Type Zeolite in Bioethanol Transformation

The decrease in stocks of traditional fossil fuels contributes to the widespread growth of interest in renewable sources of raw materials and energy. Bioethanol can become a serious alternative to traditional types of fossil raw materials and fuels due to the possibility of its widespread production from agricultural waste and wood processing. Bioethanol can be used directly as a fuel, or after transformation into hydrocarbons. The transformation of bioethanol into hydrocarbons is carried out using zeolites and zeotypes of various types, while the main problem encountered for these systems is deactivation during the catalytic transformation. In this case, one of the possible solutions to this problem is the regulation of the acidic and diffusion properties of the catalytic surface of zeolites. Changing the acidic properties can contribute to a significant increase in the stability and activity of zeolites. In this case, the variation of acidic properties is possible by combining different types of zeolites. The article presents the results of a study of a mixed zeolite of the MFI type and mordenite in the reaction of the transformation of ethanol into hydrocarbons. Zeolite synthesis was carried out by a sequential method using zeolite seed grains for the synthesis of MFI structures and n-butylamine for the synthesis of a mordenite layer. The synthesized sample was tested on a flow-type setup with a tubular reactor. The effect of temperature, specific ethanol feed rate, and total pressure in the system was investigated. An increase in the reaction temperature from 350℃ to 370℃ contributed to an increase in the rate of accumulation of liquid hydrocarbons from 0.52 to 0.64 g(HC)/(g(Cat)*h), while a further increase in temperature to 430℃ contributed to a decrease in the rate of formation of liquid hydrocarbons to 0.32 g(HC)/(g(Cat)*h). An increase in the specific feed rate of ethanol from 0.5 to 2 g(EtOH)/(g(Cat)*h) contributes to a decrease in the yield of liquid hydrocarbons. An increase in the total pressure in the system from 1 atm to 15 atm promotes an increase in the rate of accumulation of liquid hydrocarbons from 0.34 to 0.83 g(HC)/(g(Cat)*h).

Adsorption and thermal transformation of lignin model compound (ferulic acid) over HY zeolite surface studied by temperature programmed desorption mass-spectrometry, FTIR and UV–Vis spectroscopy

The adsorption of an aqueous solution of ferulic acid (FA) on protonic zeolites was studied. Three different types of zeolites and adsorption parameters (time, solid/liquid ratio, temperature and pH) were analyzed and optimized. The HY zeolite (SiO2/Al2O3 = 12) showed an adsorption percentage of 90% at 30 °C, 5 min, 10 g L−1 and pH ≤ 3. The adsorption complexes structures on the molecular adsorbates were determined by UV–Vis DRS and FTIR spectroscopies. The FA molecule interacted through phenol and carboxyl group forming monodentate and bidentate surfaces complexes (bridge and chelate). Temperature programmed desorption mass-spectrometry (TPD MS) has been used to study the decarboxylation, demethoxylation, and transalkylation processes during pyrolysis of FA surface complexes with the formation of carbon dioxide, 4-vinylguaiacol, methanol, methane, polyaromatic hydrocarbons, phenols and others.

Zeolite supported TiO2 for the degradation and mineralization of sulfamethoxazole under UV light irradiation

Zeolites have been widely regarded as promising supporting host materials for the catalyst due to their unique structure, high surface area and excellent adsorption capacity. In this work, TiO2 particles were deposited on the surface of zeolite and used as catalyst for photocatalytic degradation of sulfamethoxazole in water under UV light irradiation (365 nm). XRD, Raman spectroscopy, SEM/EDS, UV-Vis diffuse reflectance spectroscopy (DRS) and BET analysis were used to investigate the physico-chemical properties of prepared catalysts. Among prepared catalysts, TiO2/Z-500 exhibited better photocatalytic performance by achieving complete sulfamethoxazole (30 mg/L) degradation after 20 min of reaction and ~18% of TOC removal after 120 min.

Surface dealuminated Beta zeolites supported WO3 catalyst and its catalytic performance in tetralin hydrocracking

In this study, selective dealumination of Beta zeolites was performed through partially removing the templating agent in Beta zeolites by calcination and then removing the aluminum on the external surface of Beta zeolites with acid treatment. Hydrocracking catalysts were prepared by loading WO 3 onto these dealuminated Beta zeolites. It was shown that the surface SiO 2 /Al 2 O 3 of selectively dealuminated Beta zeolites was higher than that of conventionally dealuminated samples for the same bulk SiO 2 /Al 2 O 3 , and the hydrogenation activity of the catalyst of the selectively dealuminated Beta zeolites was lower than that of conventionally dealuminated Beta zeolites. The experimental results for tetralin hydrocracking to BTX showed that the catalysts based on the selectively dealuminated Beta zeolites had higher BTX selectivity and lower coke formation rate than that the catalysts based on the conventionally dealuminated Beta zeolites.

Enhanced catalytic performance of the hollow Mo/HZSM-5 nanocrystal for methane dehydroaromatization

Although Mo/HZSM-5 catalyst is widely used in the methane dehydroaromatization (MDA) reaction, the conventional microporous HZSM-5 with long diffusion path often causes the blockage of channels and pores by coke. In this work, a series of hollow HZSM-5 zeolites with different cavity sizes and tunable shell thickness were prepared by varying the alkali treatment time. After being loaded with Mo, the catalytic performances of the hollow catalysts were investigated in MDA reaction. Compared with conventional solid Mo/Z5 catalyst, the hollow Mo/Z5(x) catalysts exhibit higher CH4 conversion and C6H6 selectivity, which show an increasing trend with the increase of inner cavity size and decrease of zeolite shell thickness. Specifically, the hollow Mo/Z5(24) catalyst achieves the maximum CH4 conversion of 13.8% and C6H6 selectivity of 72%. It suggests that the hollow structure is conducive to enhance the accessibility of feed or intermediates to the Brønsted acid sites within zeolites and facilitates the rapid diffusion of the C6H6 from the intraframework channels rather than further polymerization to the coke. Furthermore, this novel structure endows stronger interaction between the Mo species and the acid sites, resisting agglomeration of Mo-species on external zeolite surface at high temperature. This research provides a new insight into exploiting a candidate catalyst for the MDA reaction.

Study on the characteristics of zeolite-promoted thermal decomposition of H2O2 for efficient NO oxidation.

The H2O2 evaporation rate directly affected the oxidation of NO by H2O2. Green zeolite and synthetic mordenite were selected to promote H2O2 thermal decomposition and NO oxidation. The effects of different zeolites, evaporation conditions, temperatures, and reactant concentrations on the NO oxidation ratio were explored. The promotion mechanism of zeolite on NO oxidation by H2O2 thermal decomposition was explained. The results show that the zeolite surface can significantly accelerate the H2O2 evaporation rate to obtain a high NO oxidation ratio. The hydrophilicity and rich pore structure of zeolite enable the rapid diffusion and evaporation of droplets on the zeolite surface. Compared with the green zeolite with the mesoporous structure, the synthetic mordenite with the hierarchical pore structure has a more obvious promotion effect on the NO oxidation by H2O2 thermal decomposition. The reason is that the synthetic mordenite contains micropores, resulting in a larger specific surface area, and the mesoporous structure is conducive to the mass transfer and diffusion of H2O2 on its surface. The product of NO oxidation is mainly NO2, which proves that ·OH plays a major role in the process.

An integrated process for struvite recovery and nutrient removal from ship domestic sewage

Marine pollution caused by the untreated and substandard discharge of ship domestic sewage has received widespread attention. A novel integrated process for struvite recovery and nutrient removal from ship domestic sewage (SRNR-SDS) based on seawater magnesium source was developed in this study. Removal efficiencies of the total nitrogen (TN) and total phosphorus (TP) for the activated sludge unit in SRNR-SDS process were approximately 67.61% and 41.35%, respectively, under the salinity of 7.85 g/L. The coupling-induced struvite crystallization unit significantly improved the removal efficiency of TN and TP, and the scanning electron microscopy and X-ray diffraction demonstrated that magnesium ammonium phosphate (MAP) crystals were successfully formed on the surface of zeolite. The SRNR-SDS process had an ideal performance for pollutant removal and MAP recovery under the optimal hydraulic retention time of 20 h. The effluent concentrations of COD, NH4+-N, TN and TP in SRNR-SDS process were approximately 34.73 mg/L, 4.31 mg/L, 10.07 mg/L and 0.23 mg/L, respectively, which meet the Chinese and international ship sewage discharge standards. SRNR-SDS process has obvious environmental, social and economic benefits, which could save 6.20%∼57.14% of the operation cost of ship domestic sewage treatment via MAP recovery. The results could provide theoretical and technical support for the development and application of ship sewage treatment process with the functions of pollutant removal and resource recovery.

A theoretical study of the effect of exchange cations in surface of ZSM-5 lamellar zeolites

The electronic properties of various cationic forms of MFI type lamellar zeolites were studied using DFT calculations and compared with their bulk counterparts. In this study, Na+ and H+ cations were considered for the effect of charge deficit compensation on the surface of lamellar zeolites. The results show that lamellar zeolites in different cationic forms exhibit two distinct band gap widths, whose values are lower than those of their bulk counterparts and arise from the surface atoms. Furthermore, the results suggest that the Na+ cation behaves as a structure-directing agent on the surface, while H+ passivates the surface of the lamellar zeolites.

Co-MOF nanosheet supported on ZSM-5 with an improved catalytic activity for air epoxidation of olefins

A composite material ZSM-5@Co-MOF containing Co-MOF and ZSM-5 was successfully prepared by steam-assisted crystallization of Co-MOF on the zeolite surface. Compared to physically mixing Co-MOF on the zeolite surfaces, Co-MOF nanosheets were uniformly attached to external surfaces of the ZSM-5 crystals because of the enhanced interaction between zeolite and Co-MOF in the composite. In addition, the Co-MOF was distributed as a nanosheet structure, and its dispersibility was greatly enhanced, in which this behavior led to more uniform distribution of the deposited active sites. Interestingly, the designed composite exhibited an excellent catalytic performance for the epoxidation of α-pinene with air. Compared to isolated Co-MOF and ZSM-5, high yield of the product (94.4%) was obtained over the 0.5ZSM-5@Co-MOF-150 composite due to the highly dispersed Co-MOF nanosheet. This opens up interesting prospects for developing new zeolite@MOF composite catalysts as efficient heterogeneous catalysts.