ZSM-5 Core Research Articles

Evaluation of Zeolite Composites by IR and NMR Spectroscopy.

In this study, we assessed the quantity, strength, and acidity of zeolite composites comprising Silicalite-1 grown on ZSM-5 crystals using a combination of infrared (IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The composites were created through the direct growth of Silicalite-1 crystals on ZSM-5 (P_ZSM-5), either with or without the organic structure-directing agent (OSDA) introduced into the ZSM-5 channels (samples: H_ZSM-5_Sil1 and TPA_ZSM-5_Sil1). The results revealed that Silicalite-1 grew differently when the ZSM-5 core was in the H+ form (empty pores) compared to when the OSDA was still present in the sample. This distinction was evident in the textural properties, with a decrease in the micropore surface area and an increase in the external surface area in the H_ZSM-5_Sil1 compared to the parent sample. The TPA_ZSM-5_Sil1 composite exhibited characteristics similar to the parent zeolite. These findings were further supported by 29Si NMR, which revealed a comparable local order for the parent (P_ZSM-5) and TPA_ZSM-5_Sil1 samples, along with a broadening of the Q4 peak for the H_ZSM-5_Sil1 composite. Additionally, the acid sites were preserved in the TPA_ZSM-5_Sil1 composite, while in the H+-form core, the concentration of Brønsted acid sites significantly decreased. This reduction in isolated Brønsted acid sites was further corroborated by 1H NMR.

ZSM-5@Zn/ZSM-5 core@shell nanocrystals as integrated catalysts for efficient methanol conversion into aromatics

The use of ZSM-5@Zn/ZSM-5 core@shell nanocrystals as integrated catalyst for efficient aromatic production from methanol aromatization is demonstrated. By combining the attributes associated with core@shell structural and acidic features, ZSM-5@Zn/ZSM-5 exhibited synergistic and improved catalytic performance toward methanol aromatization. The effect of Zn/ZSM-5 shell thickness and the acid density of the ZSM-5 core on synergistic performance was systematically investigated. Results showed that aromatic selectivity could be increased with shell thickness and the acid density of the ZSM-5 core, while catalytic stability was subject to the optimization on both shell thickness and core acid density. The strengthening of dehydroaromatization on the shell catalyst after Zn introduction and the hydrogen transfer for aromatization with increasing core acid density was confirmed. A double boost on catalytic stability from methanol conversion along with 40.7% increase on aromatic selectivity could be achieved for core@shell catalyst with a coating ratio of 0.3 compared with that on single core catalyst. The fabrication of ZSM-5 core with low SiO2/Al2O3 ratio for Zn/ZSM-5 not only provided more acid sites to promote the aromatization, but also promoted the dealkylation of the formed aromatics, which could enhance the selectivity of light aromatics and catalytic lifetime. The findings in the work not only enrich the family of core@shell composite zeolite catalysts, but also provide the fundamental understanding on the aromatization process over core@shell structural features.

Synthesis of core–shell structured zeolite nanocomposite comprising ZSM-5 core and zeolite Y shell

Zeolite core-zeolite shell synthesis is promising to enhance selective catalysis in the petrochemical industry, yet the complex synthesis poses a challenge. The successful growth of the Na-Y zeolite shell over the ZSM-5 core, producing a nanocrystalline core–shell structure, was achieved by hydrothermal crystallization via a sequential seeding-dissolution-growth route via alkaline-induced desilication of ZSM-5, followed by the addition of silica and alumina precursors to grow nanosized Na-Y crystallites over the ZSM-5 core. The successful fabrication of the core–shell structure was confirmed by different physicochemical characterizations. The optimized core–shell zeolite demonstrated noteworthy characteristics, featuring a high BET surface area of 493 m2g−1 and an external surface area of 195 m2g−1. Further, the material exhibited a connected porous network, contributing to the total pore volume of 0.52 cm3g−1. Such a strategy can be adopted to fabricate other core–shell materials for advancing the catalytic processes.

3D-printed monolithic ZSM-5@nano-ZSM-5: Hierarchical core-shell structured catalysts for enhanced cracking of polyethylene-derived pyrolysis oils

The catalytic upgrading of polyethylene-derived pyrolysis oils using ZSM-5 zeolites enables the cost-effective production of valuable chemicals from plastic waste, fostering a circular economy through resource recycling. To achieve high-performance catalyst design, balancing active site accessibility and selectivity is crucial. Here, we report a monolithic ZSM-5 @nano-ZSM-5 core-shell catalyst (mZ@nZ) fabricated via vat photopolymerization, in situ crystal engineering, and a one-step desilication-recrystallization treatment. The micromorphologies and microstructures of the core-shell catalysts are investigated using electron microscopies and physical adsorption methods. The mZ@nZ catalyst features a self-supporting face-centered cubic macrostructure with a layer of compositionally heterogeneous ZSM-5 zeolites, which comprises a catalytically benign nano-ZSM-5 shell (Si-rich) and a catalytically active ZSM-5 core (Al-rich). Abundant mesopores are created in mZ@nZ through desilication and zeolite agglomeration processes. This design offers three significant advantages: (1) enhanced active site accessibility via in situ zeolite growth, (2) surface passivation using a Si-rich shell to minimize side reactions, and (3) improved diffusion facilitated by the hierarchical structure, reducing light olefin secondary reactions and coke formation. Compared to pristine monolithic ZSM-5 and a reference pelletized catalyst, the mZ@nZ catalyst demonstrates superior performance in terms of higher light olefin yields and selectivities, with enhanced resistance to coking in the model compound and real LDPE pyrolysis oil cracking reactions. This research showcases a rational design approach at both macroscopic and microscopic scales, offering valuable insights for advancing polyolefin waste upgrading and novel zeolite catalyst design.

ZSM-5/Silicalite-1 core-shell beads as CO2 adsorbents with increased hydrophobicity

Zeolites are commonly used for selective CO2 adsorption from biogas and flue gas. One of the biggest challenges for zeolites in this application is the presence of water vapour in the raw gas streams. While zeolites with low Si/Al ratio typically display high CO2 adsorption, they are hydrophilic and H2O competes for adsorption on the active sites. On the other hand, zeolites with high Si/Al ratio are hydrophobic, but display lower CO2 adsorption capacities. In order to overcome this limitation and to combine the high CO2 adsorption capacity of low Si/Al zeolites and the hydrophobicity of high Si/Al zeolites into a single material, we designed and synthesized novel core-shell zeolitic beads comprising a ZSM-5 core and a Silicalite-1 shell. Two different strategies were employed to synthesize these macroscopic core-shell beads. In both approaches, the initial step was the synthesis of binderless ZSM-5 beads with hierarchical porosity using resin beads as hard template. In the first strategy, a shell of Silicalite-1 was synthesized on the external surface of the calcined ZSM-5 beads, yielding Sil-ZSM-A core-shell beads (0.84 ± 0.12 mm). In the second strategy, the Silicalite-1 shell was synthesized without first removing the polymeric template from the ZSM-5 beads, resulting in core-shell composite beads that after calcination yielded Sil-ZSM-B core-shell beads (0.73 ± 0.14 mm). Characterization by SEM, XRD, XRF, ICP-AES and N2 physisorption indicated that both Sil-ZSM-A and Sil-ZSM-B beads displayed the desired zeolitic core-shell structure with hierarchical porosity. Both core-shell beads showed the anticipated increase in hydrophobicity. The most promising results were obtained with Sil-ZSM-A beads, which displayed a 40% decrease in H2O adsorption capacity at 20% relative humidity (RH) and a 28% decrease at max RH compared to the parent ZSM-5 beads. At the same time, their CO2 adsorption capacity (1.94 mmol/g at 1 bar) decreased only slightly compared to the parent ZSM-5 beads (2.13 mmol/g at 1 bar). These results indicate that these core-shell beads present the desired combination of the high CO2 adsorption capacity of the ZSM-5 core with the hydrophobicity of the Silicalite-1 shell. This is a promising feature for application in the adsorption of CO2 from water-containing streams.

Polycrystalline ZSM-5@Beta core–shell composites fabricated by a seed-directed approach: A catalyst to boosting light olefin production by ordered hierarchical cracking

Featuring engineerable reaction pathway, ordered hierarchical cracking over core–shell structured zeolites (core@shell) plays a pivotal role in achieving the high-efficient conversion of low-value oil fractions into important petrochemical building blocks such as ethylene and propylene. However, the synthesis of core@shell zeolite composites with specific desirable textures is technically challenging. Herein, a novel embryo seed-breeding (ESB) approach was developed to synthesize polycrystalline ZSM-5@Beta core–shell composites (pZ@B) for boosted light olefin production. For the first time, pZ@B composites composed of a polycrystalline ZSM-5 core and a submicron-sized Beta shell was reported, which shows enhanced inner-diffusion properties and improved hydrothermal stabilities than that of conventional ZSM-5@Beta composites. In pZ@B-catalyzed reations, bulky molecules undergone a preliminary cracking into intermediate products within the Beta shell, followed by the direct diffusion into the micropores of the ZSM-5 core where they could be cracked selectively into ethylene and propylene. Compared with physically mixed zeolites and hierarchical ZSM-5, pZ@B composites showed the highest conversion and yield of ethylene and propylene in the cracking reaction of both decalin and practical industrial heavy oil. The superior catalytic activity of pZ@B can be attributed to the high accessibility of acid sites and the ordered hierarchical cracking space derived from the core–shell structure.

Hierarchical gallium-modified ZSM-5@SBA-15 for the catalytic pyrolysis of biomass into hydrocarbons

The catalytic pyrolysis of biomass is a sustainable approach for biofuel production, contributing to replacing fossil resources with renewable resources. The ZSM-5 zeolite remains an attractive catalyst in the catalytic pyrolysis of biomass, and how to reduce the product diffusion resistance and regulate the surface acidity of ZSM-5 should be explored more deeply. Herein, a hierarchical gallium-modified ZSM-5@SBA-15 catalyst is fabricated through coating a mesoporous layered SBA-15 shell on a hollow ZSM-5 core with gallium modified on the surface, which is effective for increasing hydrocarbon production during the catalytic pyrolysis of biomass process. The synergistic effect of hollowness, mesoporosity, and activity in the hierarchical gallium-modified ZSM-5@SBA-15 catalysts is found to affect the yield and quality of bio-oil. Accordingly, the hierarchical gallium-modified ZSM-5@SBA-15 catalyst with 11 wt% Ga loading exhibits a superior deoxygenation ability, and the relative content of hydrocarbons in bio-oil reach to 49.76 area% which is much higher than that of ZSM-5 (35.30 area%). Furthermore, a possible catalytic pyrolysis mechanism of biomass was also proposed to clarify the potential application of hierarchical gallium-modified ZSM-5@SBA-15 catalysts.

A core-shell structured Zn/ZSM-5@MCM-41 catalyst: Preparation and enhanced catalytic properties in propane aromatization

The core-shell ZSM-5@MCM-41 catalysts with various MCM-41 shell thickness were successfully synthesized by the epitaxial recrystallization method using hexadecyltrimethylammonium bromide (CTAB) as a template, and the corresponding Zn/ZSM-5@MCM-41 synthesized by the incipient wetness impregnation were tested in propane aromatization. Multitechniques including XRD, N2 adsorption–desorption, ICP, TEM, EDS-mapping, IR, NH3-TPD and IG were employed to investigate the physicochemical properties of Zn/ZSM-5@MCM-41 and the deactivation of carbon deposits. Results revealed that the diffusion capacities of Zn/ZSM-5@MCM-41 have been dramatically improved after the epitaxial growth of mesoporous MCM-41 shell. In addition, the non-acidic MCM-41 layer covering on ZSM-5 core could decrease Brønsted acid sites, preventing the formation of carbon deposits. Applying the protective MCM-41 shell increased the lifetime of the catalyst in comparison to Zn/ZSM-5 catalyst without the MCM-41 shell. However, the overgrowth of the MCM-41 shell with the formation of amorphous silica particles extended the diffusion path of reactants and products, which blocked the pore structure of the catalyst and reduced the catalytic properties in propane aromatization. In this sense, the controlled formation of appropriate thickness of MCM-41 shell around ZSM-5 core accounted for the enhanced catalytic properties.

Coating mesoporous ZSM-5 by microporous silicalite-1 shell: Preparation and enhanced catalytic properties in methane co-aromatization with propane

A novel core-shell structured catalyst (Zn/[email protected]) with the microporous silicalite-1 shell and the mesoporous ZSM-5 core (Zn/MZSM-5) was prepared by the epitaxial recrystallization method using tetrapropylammonium hydroxide (TPAOH) as template. Multitechniques including XRD, TEM, N2 adsorption-desorption, XPS, 27Al NMR, IR, NH3-TPD, IG and ICP were employed to investigate the physicochemical properties of the core-shell [email protected] and the deactivation of carbon deposits. Results revealed that the diffusion capacities of [email protected] have been dramatically improved after the epitaxial growth of the silicalite-1 shell. In addition, the non-acidic silicalite-1 shell covering on Zn/MZSM-5 core could decrease the external Brønsted acid sites, and thus inhibit the formation of carbon deposits. Applying the protective shell increased the stability of the core-shell catalyst in comparison to Zn/MZSM-5 catalyst without the silicalite-1 shell. However, the overgrowth of the silicalite-1 shell extended the diffusion path of reactants and products, reducing the catalytic properties in methane co-aromatization with propane. In this sense, the controlled formation of desired thickness of the silicalite-1 shell around Zn/MZSM-5 core accounted for the enhanced catalytic properties.

ZSM-5@Sil-1 core shell: Effect of synthesis method over textural and catalytic properties

A modified technique of epitaxial growth employed to produce “core-shell” catalysts coating microporous ZSM-5 with a layer of Silicalite-1 is presented in this paper. The aim was to passivate surface acidity of a ZSM-5 zeolite, in the view of potential limitation of surface effect generally responsible for coke formation. Core-shell catalysts have been synthesized starting from a ZSM-5 core with Si/Al = 25. Two different hydrothermal Silicalite-1 synthesis were performed: one using the ZSM-5 as made-form and the second using the ZSM-5H+-form as core. This allowed to investigate the effect of the organic template, filling the pores of the core, on the shell growth mechanism. Coating procedure lasted 24 h and it was repeated twice to increase Silicalite-1 thickness. All catalysts were tested for the reaction of methanol dehydration to DME in an atmospheric system at 180–240° and time on stream tests were carried out to analyse the stability of the samples. Considering the catalytic performances in terms of methanol conversion, DME selectivity and deactivation, core-shell catalysts, synthetized using an as-made form core, exhibited interesting performances, resulting from a more controlled growth of the passivating layer. These materials could constitute valid option for hybrid (Metal-Zeolite) catalyst, where the reduction of surface acidity could better stabilize the metallic function.

ZSM-5 core–shell structured catalyst for enhancing low-temperature NH3-SCR efficiency and poisoning resistance

By constructing core–shell ZSM-5@CeO2 support rather than bulk phase for loading copper, the enhanced NH3-SCR performance as well as H2O and SO2 tolerance was achieved. Cu/(ZSM-5@CeO2) catalyst exhibited the superior activity with the lowest T90 at 215 °C, which is due to the interaction between CeO2 shell and copper ions that promotes the redox properties as evidenced by oxygen isotopic exchange technique. The ZSM-5 core provides more acid sites to improve the ammonia adsorption. Thus, the highest activity of Cu/(ZSM-5@CeO2) catalyst can be ascribed to the synergistic effect of redox ability and acidity. The CeO2 shell can react with SO2 preferentially and lead to a high sulfur tolerance. This study provides a strategy for design and the practical applications of NH3-SCR zeolite catalysts.

Selective oxidation of NH3 in a Pt/Al2O3@Cu/ZSM-5 core-shell catalyst: Modeling and optimization

Modeling and optimization is presented of the Pt/Al2O3@Cu/ZSM-5 core–shell (CS) catalyst introduced in our recent study in which we successfully demonstrated the synthesis and application of the CS catalyst as an Ammonia Slip Catalyst (ASC). The commercial ASC converts NH3 to N2 using a dual-layer architecture comprising a bottom oxidation catalyst layer (supported Pt) and a top selective catalytic reduction (SCR) of NOx layer (Fe- or Cu-exchanged zeolite). The Pt/Al2O3@Cu/ZSM-5 particle, which emulates the dual-layer architecture, was shown to have superior performance due in part to an enhanced Pt activity and dense zeolite shell. A 1 + 1 D heterogeneous fixed-bed reactor containing the core–shell catalyst is developed in this study to predict the CS catalyst performance data, advance the understanding, and enable optimization. Incorporating independent kinetic models for Pt-catalyzed NH3 oxidation and Cu/ZSM-5 catalyzed NOx reduction, the reactor model predicts all of the experimental trends. The Cu/ZSM-5 kinetics are tuned using independently measured data for NH3 uptake/desorption, NH3 and NO oxidation, and standard, fast, and NO2 SCR. The particle-scale model segregates the SCR reactions from the parallel process of intracrystalline diffusion of reacting species using independently-estimated species diffusivities from diffusion-limited NH3 oxidation on a Pt/Al2O3@Na/ZSM-5. The reactor model is validated for CS catalysts having a 0.5 and 1.2 μm thick Cu/ZSM-5 shell. The tuned model is used to determine the minimum Pt loading and Cu/ZSM-5 shell thickness that achieves prescribed NH3 conversion and N2 selectivity targets. A Pt loading as low as 0.02 wt% along with 0.83 μm thick Cu/ZSM-5 is predicted to give a NH3 conversion of 70% at 250°C and a N2 selectivity at 500°C of 90%.

Enhanced Selective Oxidation of Ammonia in a Pt/Al2O3@Cu/ZSM-5 Core–Shell Catalyst

The ammonia slip catalyst (ASC) is an essential final step in the emission control system and involves the selective oxidation of NH3 to N2. The state-of-the-art ASC has a dual-layer architecture c...

Postsynthesis of hierarchical core/shell ZSM-5 as an efficient catalyst in ketalation and acetalization reactions

Hierarchical core/shell Zeolite Socony Mobil-five (ZSM-5) zeolite was hydrothermally postsythesized in the solution of NaOH and diammonium surfactant via a dissolution-reassembly strategy. The silica and alumina species were firstly dissolved partially from the bulky ZSM-5 crystals and then were in situ reassembled into the MFI-type nanosheets with the structure-directing effect of diammonium surfactant, attaching to the out-surface of ZSM-5 core crystals. The mesopores thus were generated in both the core and shell part, giving rise to a micropore/mesopore composite material. The micropore volume and the acidity of the resultant hybrid were well-preserved during this in situ recrystallization process. Possessing the multiple mesopores and enlarged external surface area, the core/shell ZSM-5 zeolite exhibited higher activity in the ketalation and acetalization reactions involving bulky molecules in comparison to the pristine ZSM-5.

Preparation of a shaped core-shell structured binder-free ZSM-5 catalyst and its application for benzene alkylation with ethylene

A kind of shaped core-shell structured binder-free ZSM-5 catalyst is prepared by re-crystallization method, from a shaped mixture of ZSM-5 zeolite and pure silica source as a binder. According to the characterization results, it is found that the silica shell, surrounding the ZSM-5 core in the shaped mixture, can be converted into ZSM-5 zeolite phase under the hydrothermal conditions with vapor-solid phase method. In this way, the catalyst with core-shell zeolite structure is consequently formed. The prepared binder-free ZSM-5 catalyst has more micro-pores than the ordinary shaped zeolite with a binder. In addition, its acidity is weakened because of the migration of framework aluminum towards the outer shell layer of ZSM-5 crystals. When applied to the vapor-phase benzene alkylation with ethylene, this catalyst shows an enhanced stability and selectivity compared to the ordinary shaped catalyst. Specially, xylene, a critical by-product formed by side reactions, is greatly suppressed over the shaped core-shell structured binder-free catalyst. In view of its good mechanical strength as well as its extended lifetime, the shaped core-shell structured binder-free ZSM-5 catalyst will be valuable in the practical industrial ethylbenzene production.

Conversion of methane to C2 and C3 hydrocarbons over TiO2/ZSM-5 core-shell particles in an electric field.

Catalytic conversion of methane (CH4) to light olefins is motivated by increasing recoverable reserves of methane resources, abundantly available in natural gas, shale gas, and gas hydrates. The development of effective processes for conversion of CH4 to light olefins is still a great challenge. The interface of ZSM-5 zeolite and TiO2 nanoparticles is successfully constructed in their core–shell particles via mechanochemical treatment with high shear stress. The oxidative coupling of methane at a low temperature under application of an electric field may be induced by the O2 activation via electrons running through the surface of TiO2 located at the interface of TiO2 and zeolite particles. Moreover, C3H6 was also produced by the ethylene to propylene (ETP) reaction catalyzed by Brønsted acid sites in the ZSM-5 zeolite within core–shell particles.

Ultrafast post-synthesis treatment to prepare ZSM-5@Silicalite-1 as a core-shell structured zeolite catalyst

Abstract Post-synthesis treatment is an effective way to modify zeolites to acquire desirable properties. Here, we present an ultrafast post-synthesis treatment to prepare core-shell structured zeolite, which is composed of a ZSM-5 core and a silicalite-1 shell. The pure silica shell, which is aimed to remove the Bronsted acid sites associated with the framework Al on the external surface of aluminosilicate core, was formed unprecedentedly within several minutes by our method. Complementary techniques, such as XRD, TG/DTA, SEM, TEM, ICP, and XPS, were employed to verify the successful coverage of the silicalite-1 shell onto the ZSM-5 core. By adjusting the treating period, temperature, and reactant compositions, the thickness of the shell can be easily tuned. Further, this ultrafast process enabled the establishment of a continuous flow reaction system, which could allow the mass production of core-shell structured zeolite catalysts.

Increasing resolution of selectivity in alkene hydrogenation via diffusion length in core-shell MFI zeolite

We designed a core-shell zeolite structure comprises of palladium-deposited ZSM-5 core and silicalite-1 (S-1) shell which favors selectivity towards light olefin in hydrogenation via increased diffusion length. A well designed S-1/Pd/ZSM-5 core-shell structure was prepared via secondary crystallization of S-1 layer on the Pd/ZSM-5 core. The catalytic and selectivity performance of the S-1/Pd/ZSM-5 composite was evaluated in catalytic hydrogenation of alkenes in liquid phase. The synthesized S-1/Pd/ZSM-5 gives a much higher selectivity towards 1-hexene (87%) over cyclohexene (13%) even though both reactants are able to enter the 10-membered ring channels of the core-shell structure. The zeolitic core-shell composite also showed an increasing selectivity towards 1-hexene over 1-heptene as the S-1 layers built up, even though both are linear alkenes with similar kinetic diameter that are accessible to the MFI framework. In this work, we demonstrate a strong correlation between the thickness of the S-1 shell layer and the selectivity towards light olefins due to faster mass transfer rate. The design of the core-shell MFI structure is a new example of how selectivity in a zeolite-catalyzed reaction can be changed and enhanced without relying on typical molecular size exclusion process.

Fabrication of hollow spheres composed of nanosized ZSM-5 crystals via laser ablation

Zeolite spheres with a core-shell structure were fabricated by a combination of pulsed laser deposition (PLD) and vapor-phase crystallization. Spherical mesoporous DAM-1 or SBA-15 was used as the silicon source and substrate. After vapor phase treatment hollow spherical shells consisting of nanosized ZSM-5 crystals were formed. In addition, the size of the ZSM-5 crystals in the shell ranges from 5 to 500 nm which can be adjusted by changing the crystallization time (3–5 days) or the PLD coating thickness. The deposition rate was 13 nm/min at 120 mJ and 6.5 nm/min at 70 mJ. The ZSM-5 core–shell structure was characterized by XRD, IR, SEM and N 2 absorption. The dissolution of the mesoporous silica substrate and transport of the resulting silica species to the growing ZSM-5 film during vapor-phase crystallization is discussed in terms of a solution mediated transport mechanism.

Synthesis and characterization of colloidal zoned MFI crystals

Colloidal zoned MFI crystals, i.e., continuous crystals with a compositional gradient resulting in a ZSM-5 core covered with a silicalite-1 shell, were synthesized by the addition of ZSM-5 seeds to a silicalite-1 synthesis solution. The effect of the surface aluminum content of the ZSM-5 crystals on the synthesis of the zoned MFI crystals was investigated using SEM, TEM, XPS and XRD. An acid treatment of the ZSM-5 seeds, which removed some of the aluminum at the surface, proved favorable for the synthesis of zoned MFI crystals.