ZSM-5 Zeolite Research Articles

Efficient synthesis of phosphorus-promoted and alkali-modified ZSM-5 catalyst for catalytic dehydration of lactic acid to acrylic acid

This study presents a novel one-pot synthesis method for phosphorus-enhanced ZSM-5 zeolite, followed by post-synthesis alkali treatment. The resulting catalyst is designed for the sustainable production of acrylic acid (AA) from lactic acid (LA). Adding phosphorus as a promoter during synthesis significantly improved the acid-base properties of the zeolite. Additionally, the alkali treatment contributed to the overall optimization of the catalyst’s performance. Comprehensive analytical techniques, including XRD, BET, FT-IR, TGA, XPS, ICP-MS, DRIFT spectra, NH3, and CO2-TPD, were employed to elucidate the structural and acid-base properties of the ZSM-5/P-Na catalyst. Finally, an experimental design was developed to optimize the important operational variables in the LA dehydration reaction. The optimized ZSM-5/P-Na catalyst demonstrated excellent performance, achieving 83% AA selectivity and 98% LA conversion with a long catalytic lifetime of 50 h. This research demonstrates a promising approach for developing efficient catalysts for sustainable AA production.

Highly para-selective alkylation of toluene by methyl mercaptan over silylated ZSM-5 zeolite

Friedel-Crafts alkylation of toluene with methyl mercaptan has been investigated in the presence of H-ZSM-5 and SiO2/H-ZSM-5 catalysts. The silica layers have been built on H-ZSM-5 zeolite by chemical liquid deposition of tetraethyl orthosilicate. The passivation with silica of the external surface of H-ZSM-5 zeolite has been confirmed by FT-IR spectroscopy and mesitylene isomerization, used as a model reaction. All catalysts exhibited notable behavior in the alkylation of toluene to xylenes. Efficiencies higher than 98 % in alkylation for both toluene and methyl mercaptan were obtained at 375 °C. In terms of para-selectivity, outstanding performance was revealed by the silylated zeolites. Thus, over 12 % SiO2/H-ZSM-5, at 375 °C and WHSV = 9.4 gtoluene+CH3SH gcat-1h−1, the para-xylene selectivity was close to 100 %. The experimental apparent activation energy for the toluene alkylation with methyl mercaptan catalyzed by H-ZSM-5 was 80 kJ/mol.

A two-step hydrothermal synthesis of fly-ash-based ZSM-5 zeolite and its catalytic properties in NO removal

The pursuit of carbon peaking and carbon neutrality goals necessitates flexible operation and deep peaking of coal-fired units, thus placing heightened demands on nitrogen oxide (NOX) emission control. Fly ash, a solid waste rich in silicon (Si) and aluminum (Al), should be fully leveraged, and the high-value synthesis of zeolite represents a viable utilization method. In this context, fly ash-based zeolite was prepared as a catalyst to facilitate the generation of active oxides from H2O2, combined with alkali solution absorption, to achieve efficient denitrification. This approach effectively transforms ‘waste to pollution’ mitigation. The optimal synthesis conditions for FA-ZSM-5 zeolite were established using the alkali fusion hydrothermal synthesis method, with fly ash as the raw material. The specified conditions were NaOH/FA = 1.2, SiO2/Al2O3 = 40, H2O/Al2O3 = 1325, TPAOH/Al2O3 = 10, ZSM-5-seed addition of 5 %, and a hydrothermal temperature and time of 140 °C for 24 h. Experimental parameters were meticulously investigated to ascertain their impact on nitric oxide (NO) removal efficiency. The highest removal efficiency was achieved under specific conditions: a reaction temperature of 140 °C, an H2O2 concentration of 6 %, a catalyst dose of 0.3 g, an NO concentration of 600 mg/m3, and an SO2 concentration of 1000 mg/m3. Finally, analysis of the catalytic oxidation mechanism revealed that H2O2, when catalyzed by FA-ZSM-5 zeolite, generates ·OH radicals with strong oxidizing properties, thereby facilitating the oxidative removal of NO.

The Synthesis of Granular ZSM-23 Zeolite with a High Degree of Crystallinity and a Micro-Meso-Macroporous Structure, and Its Use in the Hydroisomerization of n-Hexadecane

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.

Mesoporous Cu-doped ZSM-5 zeolite for efficient radical-mediated decarboxylative silylation

Vinylsilane compounds are essential chemical feedstocks and intermediates in organic synthesis. A heterogeneous Cu-containing mesoporous ZSM-5 zeolite catalyst developed through an in-situ doping method can be used for preparing vinylsilane compounds via decarboxylative coupling with remarkable catalytic efficiency. The mesoporous structure along with the appropriate surface area and pore volume of the catalyst is likely to be responsible for facilitating mass transfer in the reaction process. Additionally, due to the suitable Brønsted and Lewis acid active sites, adsorption and activation of reactant molecules can be readily triggered to promote the generation of alkoxyl radicals, which is the crucial species to complete the catalytic cycle. Importantly, the transformation exhibits high efficiency, broad substrate scope, and good reusability for at least six cycles.

Dynamics of water, CO2, ethane and their mixtures in ZSM-22 zeolite: the role of polarity and hydrogen bonding

Abstract Understanding the interplay between confinement effects and intermolecular interactions is essential for predicting molecular diffusion in zeolites. In this study, we investigate the diffusion behavior of ethane, CO2, and water in ZSM-22 molecular sieves, focusing on the effects of mixing these fluids. Our results reveal that while CO2 has minimal impact on ethane diffusion, water significantly slows ethane’s motion by forming molecular bridges across the pore structure, reducing ethane’s diffusion by up to 30%. Ethane, in turn, restricts water’s mobility, and reduces the water–water coordination number from 2.22 to 0.73 depending on concentration. The diffusion of CO2 in mixtures shows a 40% increase in pure state under confinement. The role of polarity and hydrogen bonding is crucial, with water molecules exhibiting 1.2 hydrogen bonds in the confined state—much lower than the 3.4 bonds in bulk water. Molecular rotation in ZSM-22 of all fluids occurs at two distinct time scales: the short-time fast rotation dominated by molecular inertia and the long-time rotation hindered by fluid-zeolite interactions. For water, hydrogen bonding further restricts full rotational freedom. These findings provide a comprehensive understanding of how ethane, water, and CO2 interact and diffuse in nanoporous materials.

Production of γ-valerolactone from furfural by core-shell ZSM-5 supporting Ru-Zr bimetals through enhanced cascade reaction

In this study, a catalyst comprising Ru-Zr bimetals supported on core-shell ZSM-5 zeolite is tailored for catalytic conversion of furfural to yield γ-valerolactone via promoted two-step cascade reaction. ZrO2 encapsulated within hierarchical ZSM-5 zeolite is synthesized via a one-pot hydrothermal method, followed by sequential treatment with NaOH to yield Zr@ZSM-OH. Subsequently, the RuO2 component is introduced through impregnation, followed by calcination to obtain Ru-Zr@ZSM-OH. In conversion of furfural, the synergistic effect of highly dispersed ZrO2 acting as Lewis acid sites, combined with Brønsted acid sites provided by zeolite, facilitates the production of isopropyl levulinate via catalytic hydrogenation transfer, under either H2 or N2 atmosphere. In the secondary step, the introduced RuO2 promotes the adsorption and spillover of active H2, thereby accelerating the conversion of isopropyl levulinate to γ-valerolactone. The as-synthesized Ru-Zr@ZSM-OH catalyst achieves an impressive yield of 92.6 wt% of γ-valerolactone after just a 2 h reaction at 175 °C.

Flexible ZSM-5 Zeolite Membrane for High-Performance Helium Separation.

Flexible zeolite membranes are promising for scalable and adaptable separation of critical gases such as helium; however, the synthesis of such membranes remains a significant challenge. In this study, we report the successful fabrication of crack-free ZSM-5 zeolite membranes on polytetrafluoroethylene (PTFE) supports using a seeded growth method. PTFE-supported membranes exhibit unprecedented helium permeance of over 6.7×10-7 mol m-2 s-1 Pa-1 and high He/N2 and He/CH4 separation factors of 17 and 83 respectively, surpassing current state-of-the-art membranes. These flexible membranes maintain excellent separation performance even after bending and stretching. Furthermore, large-scale membranes demonstrate stable helium separation from multicomponent gas mixtures, showcasing their significant potential for practical helium extraction from natural gas.

Cerium-induced modification of acid-base sites in Ni-zeolite catalysts for improved dry reforming of methane

Dry reforming of methane (DRM) is a promising route to mitigate greenhouse gas emissions by converting CH4 and CO2 into valuable syngas. The present work explores the effect of Ce addition to Ni-based catalysts supported on CBV3020E (ZSM-5) for DRM. The use of Ce as a promoter to tune the acid-base properties of zeolites for DRM is addressed for the first time in detail. While Ce has traditionally been used to improve oxygen storage capacity, this work explores its novel use as a means to enhance surface basicity and promote CO2 adsorption. The samples were prepared by wet impregnation, characterized using N2-sorption, X-ray diffraction, H2-temperature-programmed reduction, temperature-programmed desorption of CO2 and ammonia, and Fourier transforms infrared spectroscopy, and tested for DRM at 800 °C and 42,000 mL/g.h GHSV. Results show that ZSM-5 zeolite can be beneficial in achieving high metal dispersion. The introduction of 2 wt% Ce to Ni5/ZSM-5 increases the concentration of strong basic sites, resulting in improved catalytic performance from 37 % CH4 conversion and 48 % CO2 conversion for Ni5/ZSM-5 to 55 % and 65 % on promoted Ni5Ce2/ZSM-5, respectively. Thus, the best results are observed on Ni5Ce2/ZSM-5 and an optimal H2/CO ratio of 0.84 is achieved in this case. Upon decreasing GHSV to 15,000 mL/g.h, CH4 and CO2 conversions jump to 83 % and 88 %, respectively on Ni5Ce2/ZSM-5. Cerium doping produces more desirable strong basic sites and enhances NiO reducibility. This promotes CO2 adsorption and drives the catalytic reaction towards syngas formation, which eventually results in increased efficiency and improved performance.

Kinetic modeling of the removal of phenolic compounds from olive mill wastewater by hierarchical zeolite/carbon nanotubes: Isotherm, kinetics, and thermodynamic

ABSTRACT In this study, plain zeolite (ZSM5) and hierarchical zeolite (H-ZSM5) were synthesized as efficient adsorbents for the removal of polyphenolic/antioxidant compounds from olive mill wastewater (OMW). The XRD and FTIR results confirmed the successful synthesis of ZSM5 zeolites. SEM images and BET demonstrated that H-ZSM5 possessed a markedly greater surface area of 337.99 m2/g in contrast to ZSM5 (162.84 m2/g). For H-ZSM5, the values determined for pore volume, total volume, and pore diameters are 77.655 cm3 g−1, 0.1844 cm3 g−1, and 2.1826 nm. The absolute zeta potential values varied between 5.36 ± 1.21 and − 46.41 ± 1.32 mV, with the peak absolute value of − 46.41 ± 1.32 mV occurring at pH 4. The optimal conditions for the removal of phenolic compounds, achieving an efficiency exceeding 90%, were identified as a pH of 4, an adsorbent dosage of 50 mg, and a contact duration of 90 minutes. The adsorption isotherm was found to align with the Langmuir model rather than the Freundlich model, indicating a monolayer adsorption capacity of 48.7 mg/g. Kinetic studies were consistent with a pseudo-first-order model (R2 >0.99). Ultimately, the thermodynamic analysis suggested that the adsorption of OMW onto ZSM5 is both spontaneous and governed by a physisorption mechanism.

Boosting hydroisomerization of n-hexadecane by designing core-shell bifunctional catalysts with partially blocked micropores

Hydroisomerization of long-chain n-alkanes is an indispensable route for upgrading fossil fuels and lubricant oils to meet the state of art regulations. Precisely regulate the distribution of acidic and metal active sites to suppress unwanted cracking reaction is hitherto a difficult task. In this work, we develop a simple coating-carbonation strategy for constructing novel core-shell bifunctional catalysts, comprising ZSM-22 zeolite core with the partially blocked channels and Pt nanoparticles loaded on the mesoporous SiO2 shell. The unique treatment not only adjusted the distribution of acid sites located within the micropore channels and external surface, but also alter the locations and dispersion of Pt nanoparticles. Owing to the short diffusion lengths, nanoscale distance between acid sites and Pt species, and high metal dispersions, the core-shell bifunctional catalyst exhibits outperformed performance in n-hexadecane hydroisomerization, i.e., the yield of isomerized hexadecane can reach 87.9 %, which is among the relatively high level compared with the previous reported Pt/zeolite counterparts. Moreover, the catalyst also displays excellent stability (no deactivation within 100 h). The disclosed structure-catalysis relationship provides rational reference for designing the synergistic meta-acid active sites in the hydroisomerization of long-chain n-alkanes.

Enhanced Removal Performance and Economical Efficiency of Volatile Organic Sulfur Compounds by Silver-Modified ZSM-5 Zeolites under a High-Humidity Environment: A Mechanistic Study of the Adsorption-Plasma Catalytic Process.

Dimethyl sulfide (DMS) is a harmful volatile organic sulfur compound (VOSC), which must be effectively controlled. The adsorption-plasma catalytic (APC) process is an efficient and economical route for the elimination of low-concentration VOSCs; however, there are still many challenges in humid environment. In this study, a series of zeolites with different Si/Al ratios and Ag loadings were designed, and were performed for DMS removal by APC process. At 80% relative humidity, the DMS adsorption capacity of Ag5-ZSM25 reached 33.9 mg/g, which was 7.9 times that of ZSM25 and nearly 2 times that of Ag5-ZSM200. Analyses via UV-vis, X-ray photoelectron spectroscopy (XPS), and CO-FTIR confirmed that Ag+ was the predominant species for DMS adsorption and degradation in Ag5-ZSM25. DMS-temperature-programmed desorption (TPD) and density functional theory (DFT) calculations indicated that Ag+ significantly enhanced the binding energy with DMS and weakened the competitive adsorption impact of H2O. In the plasma regeneration stage, Ag5-ZSM25 demonstrated an 89% mineralization, with Ag+ being crucial for DMS mineralization. Based on the in situ plasma DRIFT spectra, a possible degradation pathway for DMS was proposed. The APC process achieved an energy efficiency of 1.66 g/kWh, tripling that of the continuous plasma catalytic process and providing guidance for low-concentration DMS elimination.

Deoxygenation and isomerization activity balance for NiMo/ZSM-23 catalysts as an effect of Mo/(Ni+Mo) ratio in hydroprocessing of fatty acids

Series of Ni-Mo catalysts based on ZSM-23 zeolite were synthesized by incipient wetness impregnation – with a fixed content of Ni (5 wt. %). These catalysts were tested in a hydroprocessing of a mixture of fatty acids (C16-C18) in a flow reactor at a temperature of 300 °C, a pressure of 2.5 MPa and WHSV = 8.4 h-1. The influence of the ratio of metals on the formation of forms of the active component, as well as on the activity, selectivity to iso-alkanes and the stability of catalysts during the hydroprocessing of a mixture of undiluted fatty acids was determined. The ratio of metals was investigated in the range from 0 to 1. The highest deoxygenation activity and highest isoalkanes yield were found for sample with Mo/(Ni+Mo) ratio equal 0.25, in which, according to the XPS, the Mo/(Ni+Mo) ratio on the surface is 0.4.

Unveiling the generation of mesoporous MFI zeolites with one-dimensional fins in the assistance from small quaternary ammonium cation and its application in propane aromatization

In this work, a kind of ZSM-5 zeolite with one-dimensional fins growing along the [010] direction has been successfully synthesized utilizing both tetrapropylammonium hydroxide (TPAOH) and tetramethylammonium hydroxide (TMAOH) as co-templates. With the aid of molecular dynamic simulations and a series of experimental evidences, the formation mechanism of the one-dimensional feature is determined to arise from the synergic effects between TPA+ and TMA+. Two TPA+ and three TMA+ would co-exist in a unit MFI cell at a certain crystallization period depending on the composition of zeolite and precursor, and this configuration ensures a minimum stabilization energy required for the growth along [010] direction. Investigations manifest these needle-like fins with diameters of ca. 60 nm could function as pseudo nano crystals and introduce additional pores ranging from 10 to 90 nm, which effectively promotes the diffusion capability and substantially improves the catalytic performance in propane aromatization.

Constructing ZSM-5 loaded with 2-mercaptobenzimidazole on glass fiber for enhancing the anti-corrosion and erosion resistance properties of epoxy coating

Glass fiber reinforced polymer coatings (GFRPC) are used to protect steel structures in harsh marine environments due to high mechanical strength and chemical stability. The composite coating not only suffers from impact damage by seawater and sediment but also experiences corrosion damage in the splash zone. However, the GF has weak interfacial adhesion with polymer resins due to the chemical inertia and smooth surface, which limits the service lifespan of GFPRC. Hence, ZSM-5 zeolite were in situ prepared on the surface of glass fibers by hydrothermal synthesis, and 2-mercaptobenzimidazole (MBI) was further adsorbed to obtain difunctional hybrid glass fibers (ZGFM) to enhance the interfacial adhesion strength of glass fiber/resin and also the erosion resistance and anti-corrosion ability of composite coatings. Compared to GF/EP, the interfacial shear strength of ZGFM/EP was increased by 104.39 %. After immersion under an alternating hydrostatic pressure of 20 MPa for 12 days, the impedance value of the ZGFM/EP composite coating remained at 6.40 × 109 Ω•cm2, demonstrating outstanding deep-sea anti-corrosion performance. Following the erosion test, the ZGFM/EP exhibited a reduction in mass loss and volume loss by 10.65 % and 12.55 %, respectively, in comparison to the pure EP coating. The excellent interfacial strength between ZGFM and EP ensured effective stress transfer, which prevented crack propagation, thus enhancing the mechanical properties and erosion resistance of the composite coating. Meanwhile, electrochemical experiment proves glass fiber with MBI loaded obviously inhibits the corrosion reaction.

Directional Transport in Hierarchically Aligned ZSM-5 Zeolites with High Catalytic Activity.

Zeolites, the most technically important crystalline microporous materials, are indispensable cornerstones of chemical engineering because of their remarkable catalytic properties and adsorption capabilities. Numerous studies have demonstrated that the hierarchical engineering of zeolites can maximize accessible active sites and improve mass transport, which significantly decreases the internal diffusion limits to achieve the desired performance. However, the construction of hierarchical zeolites with ordered alignments and size-controlled substructures in a convenient way is highly challenging. Herein, we develop a facile procedure using two common structure-directing agents, tetrapropylammonium hydroxide (TPAOH) and tetraethylammonium hydroxide (TEAOH), to synthesize hierarchically aligned ZSM-5 (Hie-ZSM-5) crystals with a-axis alignment substructures of controllable size. The control of the substructure size (α) in the range of 10-60 nm and the corresponding similarity (r = α/β, where β is the size of Hie-ZSM-5) ranging from 0.004 to 0.033 can be tuned by varying the Si/Al ratios (40-120). A systematic investigation of the overall crystallization process, using time-dependent XRD, SEM, TEM, and solid-state magic-angle spinning NMR (13C, 27Al, 29Si) methods, enable us to construct a solid mechanism for the generation of Hie-ZSM-5. Most importantly, directional transport in the unique structures of Hie-ZSM-5 efficiently enhances mass diffusion, as well as catalytic activity and stability. These findings improve our understanding of the zeolite crystallization process and inspire novel methods for the rational design of hierarchical zeolites.

Rapid Synthesis of Self-Pillared ZSM-5 Zeolite Nanosheets with Enhanced Catalytic Performance in n-Octane Cracking

Rapid Synthesis of Self-Pillared ZSM-5 Zeolite Nanosheets with Enhanced Catalytic Performance in <i>n</i>-Octane Cracking

Facile synthesis and mechanistic insights into ZSM-5 aggregates via a mesoporogen-free route

Developing hierarchical zeolites is highly important for catalytic applications. In this study, micro- and submicron-sized hierarchical ZSM-5 zeolites, composed of aggregated nanosized ZSM-5 crystals, were facilely synthesized without any mesoporogen. The effects of the gel composition in a mesoporogen-free system on the formation of ZSM-5 aggregates were studied. The results revealed that the Na2O/SiO2 molar ratio and the aluminum source exerted significant impacts. Furthermore, we demonstrated that the morphology and size of the ZSM-5 aggregate could be easily adjusted by varying the gel composition. Mechanistic insights indicated that the formation of hierarchical ZSM-5 aggregates in the mesoporogen-free system likely followed a space-confined growth mechanism.

Bifunctional Catalytic Performance of Zn/ZSM-5 in the Aromatization of LPG and the Conversion of Pyrolytic Gases from Recycled Polypropylene

Zn-modified ZSM-5 zeolites with different zinc contents were successfully prepared by the impregnation method and compared with unmodified ZSM-5. Their potential for LPG (liquefied petroleum gas) aromatization and the conversion of pyrolysis gases obtained from recycled polypropylene was subsequently evaluated. In this process, various characterization tests were performed on the prepared catalysts, including SEM-EDS (scanning electron microscopy with energy-dispersive spectroscopy), TPD-NH₃ (temperature-programmed desorption of ammonia), and FTIR (Fourier-transform infrared spectroscopy). Under optimized conditions, the best results were obtained with 2% Zn/ZSM-5, which generated a higher production of BTX (benzene, toluene, and xylene) isomers, which are major components of gasoline. Likewise, in catalytic pyrolysis of recycled polypropylene, this catalyst generated a higher production of aromatic compounds. Therefore, this catalyst showed excellent performance in generating valuable hydrocarbons of great industrial interest, particularly aromatics.

Intergrowth MFI Zeolite with Inverse Al Zoning and Predominant Sinusoidal Channels for Highly Selective Production of Styrene.

ZSM-5 zeolites with accessible micropore architecture and tunable acid-base sites are important shape-selective catalysts. However, the presence of exposed straight channels and the external acid-base sites of conventional ZSM-5 has a negative impact on shape selectivity. Herein, we report on the direct synthesis of an intergrowth ZSM-5 zeolite mimicking the mortise-tenon joints. It can be revealed by various methods that the mortise-tenon ZSM-5 shows an inverse Al gradient from the surface to the core of the zeolite. More importantly, the sinusoidal channels predominantly opened to their external surfaces are constructed. The shape-selective capability of the ZSM-5 zeolite has been fully exploited due to the intrinsic inert external surface and unique sinusoidal channel features, thereby resulting in high styrene selectivity (>90%) and good catalytic stability (>100 h) in the toluene side-chain alkylation reaction. In addition, in situ DRIFTS confirms that this intergrowth ZSM-5 contributes to the formation of more active intermediates of HCOO* and H3CO*, which is another reason responsible for the superior performance.