Silicalite-1 Shell Research Articles

Advancing highly selective low-temperature ammonia oxidation: Hydrophobic silicalite-1 shell confining silver nanoparticles on Cu/ZSM-5 core

A judiciously devised core–shell NH3-SCO catalyst featuring a Cu/ZSM-5 core enveloped by an Ag/silicalite-1 shell (Cu/ZSM-5@Ag/S-1) was rationally constructed. Integrating the silicalite-1 shell effectively suppresses the migration of Ag into Cu/ZSM-5 core, conserving the active Cu2+ sites for the catalytical conversion of byproducts NOx. Concurrently, the shell averts the formation of positively charged Ag species, facilitating the generation of abundant Ag0 nanoparticles encapsulated in the S-1 shell. Comprehensive characterizations reveal abundant Ag0 species within the core–shell Cu/ZSM-5@Ag/S-1 catalyst, boosting O2 activation and NH3 dehydrogenation and thereby contributing to superior low-temperature activity in NH3-SCO reactions. Furthermore, the hydrophobic S-1 shell effectively reinforces the hydrothermal stability of the core–shell Cu/ZSM-5@Ag/S-1. DRIFTS coupled with DFT studies elucidate that the core–shell sample follows the imide mechanism, while the shell-free sample adheres to the hydrazine mechanism. This work advances our understanding of catalyst design and presents a promising solution with practical implications for ammonia oxidation processes.

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.

Silicalite-1 Layer Secures the Bifunctional Nature of a CO2 Hydrogenation Catalyst.

Close proximity usually shortens the travel distance of reaction intermediates, thus able to promote the catalytic performance of CO2 hydrogenation by a bifunctional catalyst, such as the widely reported In2O3/H-ZSM-5. However, nanoscale proximity (e.g., powder mixing, PM) more likely causes the fast deactivation of the catalyst, probably due to the migration of metals (e.g., In) that not only neutralizes the acid sites of zeolites but also leads to the reconstruction of the In2O3 surface, thus resulting in catalyst deactivation. Additionally, zeolite coking is another potential deactivation factor when dealing with this methanol-mediated CO2 hydrogenation process. Herein, we reported a facile approach to overcome these three challenges by coating a layer of silicalite-1 (S-1) shell outside a zeolite H-ZSM-5 crystal for the In2O3/H-ZSM-5-catalyzed CO2 hydrogenation. More specifically, the S-1 layer (1) restrains the migration of indium that preserved the acidity of H-ZSM-5 and at the same time (2) prevents the over-reduction of the In2O3 phase and (3) improves the catalyst lifetime by suppressing the aromatic cycle in a methanol-to-hydrocarbon conversion step. As such, the activity for the synthesis of C2 + hydrocarbons under nanoscale proximity (PM) was successfully obtained. Moreover, an enhanced performance was observed for the S-1-coated catalyst under microscale proximity (e.g., granule mixing, GM) in comparison to the S-1-coating-free counterpart. This work highlights an effective shielding strategy to secure the bifunctional nature of a CO2 hydrogenation catalyst.

Effects of Silicalite-1 Coating on the p-Xylene Selectivity and Catalytic Stability of HZSM-5 in Toluene Methylation with Methanol

The methanol–toluene alkylation process over zeolites catalysts offers a promising route for the production of p-xylene from low-cost feedstocks. Herein, we present a catalyst by preparing a core-shell aluminosilicate zeolite with an epitaxial silicalite-1 shell that passivates acid sites on the exterior surfaces. The para-selectivity was obviously increased due to the inhibition of the unselective isomerization of p-xylene over the external acid sites, and the open porous structure of the silicalite-1 shell ensured the mass transfer of reactants and products. Meanwhile, the carbon deposition was suppressed over HZSM-5@silicalite-1 catalysts, as a result of the decreased external acid sites. Furthermore, pulse chromatographic experiments revealed that the silicalite-1 coating could also improve the separation efficiency of p-xylene over o-xylene and m-xylene, due to the steric hindrance and extended diffusion path, resulting in a higher selectivity for p-xylene compared to that of the parent HZSM-5. The HZSM-5@4%S-1 catalyst showed the highest p-xylene selectivity (>80%) and methanol efficiency (66%), with good catalytic stability throughout the 170 h reaction time.

Enhanced shape-selective-desulfurization performance of CuY@silicalite-1 core-shell composites with highly dispersed Cu2+ active adsorption sites

An improved CuY@silicalite-1 core-shell composite was developed with a higher shape-selective adsorption desulfurization performance of DMDS from MTBE solution (88.5 mgs/gadsorbents). By isolating the bidirectional chemical environments via a resin interlayer between Y zeolite and silicalite-1 shell, ethylenediamine modification (NH2-(CH2)2-NH2, EDA) was further applied after alkali treatment as a connecting bridge between Cu2+ and Y zeolite. During which, one of the -NH2 terminal groups of EDA could bind to Si-OH and the other -NH2 could complex with Cu2+. The results showed that alkali treatment for 2 h, Y: EDA= 1: 0.1, Cu2+ concentration of 0.05 mol/L, EDA and Cu2+ infiltration for 8 times could maximize the sulfur adsorption capacity of the synthesized core-shell composite. And in addition to an excellent sulfur adsorption activity according to adsorption kinetics and isotherms analysis, CSR-CuYOH(0.1–0.05–8) also presented good stability even after 6 cycles of regeneration.

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.

Controlling the bidirectional chemical environments for high-performance Y@silicalite-1 core-shell composites in shape selective desulfurization

• Alkali and Cu 2+ are used to tune the structure and increase active sites of Y zeolite. • Resin layer and EDA can provide stable external environment for silicalite-1 shell. • Selective-adsorption achieved 75.58 mg/g, double of 37.1 reported previously. • Extraction before calcination kept 92% desulfurization rate after 6 regeneration cycles. A high-performance Y@silicalite-1 core–shell composite for shape- selective adsorption desulfurization was synthesized by controlling the bidirectional chemical environments via a resin interlayer between Y zeolite core and silicalite-1 shell. In this process, the alkali treatment, Cu 2+ ion-exchange, Cu 2+ equal volume impregnation, resin coating and ethylenediamine modification were applied to work collaboratively for a high shape selectivity and high sulfur adsorption capacity. Results showed that alkali treatment for 2 h, TEOS:Y = 4, Y:3-aminophenol = 1:1, Y: EDA = 1:1 and 550 °C calcination could endow the synthesized core–shell structured composite with a high-performance in shape-selective adsorption desulfurization of DMDS from MTBE solution with a maximum sulfur adsorption capacity of 75.58 mg s /g adsorbents , which was more than double of the best DMDS sulfur adsorption capacity from MTBE (37.07 mg s /g adsorbents ) reported previously. The adsorption kinetic and isotherm analysis indicated that the adsorption of DMDS on Y zeolites was monolayer-chemisorption process, and the corresponding theoretical saturated adsorption capacity could reach up to 84.6 mg s /g adsorbents . The regeneration capability can be effectively improved by ethanol extraction before calcination, retaining a high desulfurization rate level at more than 92% even after 6 cycles.

Performance of mesoporous HZSM-5 and Silicalite-1 coated mesoporous HZSM-5 catalysts for deoxygenation of straw fast pyrolysis vapors

•Catalytic treating of biomass fast pyrolysis vapors offers a promising route to convert many different types of lignocellulosic biomass into biofuels. Considerable research efforts have focused on using zeolite catalysts, especially the microporous HZSM-5 zeolite. Unfortunately, the zeolite’s initial high activity in forming coke and light gases reduces the overall oil yield. In this contribution, we synthesized conventional HZSM-5 zeolite, mesoporous HZSM-5 zeolite, and a core-shell catalyst consisting of mesoporous HZSM-5 zeolite coated with a thin layer (<20 nm) of silicalite-1 zeolite. The catalysts were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 and Ar physisorption, temperature programmed desorption of ammonia (NH3-TPD), diffuse reflectance infrared fourier transform spectroscopy (DRIFT) spectra, and 27Al nuclear magnetic resonance (NMR). The catalysts were tested in a tandem micro-pyrolyzer system for deoxygenation of wheat straw derived fast pyrolysis vapors in a downstream catalytic fixed bed reactor and the quantitative product analysis was performed with GC-MS/FID/TCD and TGA-MS. The change in yields of different product groups was monitored during catalyst deactivation for an increasing number of pyrolysis vapor pulses and the cumulative carbon recoveries of all product streams (char, vapors, gas, and coke) were compared at different biomass-to-catalyst ratios (∼4 and ∼1) for catalyst loadings of 2 and 8 mg, respectively. In addition, the yields were compared for the same number of zeolitic acid sites. Even though the coking propensity was highest for the mesoporous HZSM-5 (5.1% carbon recovery of fed biomass at B:C = 1), it showed improved conversion of oxygenates (wt% O of vapors = 15) and a higher tolerance towards deactivation by coking compared to the conventional HZSM-5 (wt% O of vapors = 20). Coating of mesoporous HZSM-5 with silicalite-1 reduced the number of acid sites per mass of catalyst by ∼20%, which is attributed to the addition of the inert silicalite-1 layer and passivation of the external acid sites of the mesoporous HZSM-5. Compared to mesoporous HZSM-5, the added silicalite-1 shell reduced the coke yield by 43% (from 5.1–2.9 wt% of fed biomass carbon) for the same catalyst mass and by 8% (4.7 wt% of fed biomass carbon) for the same total number of acid sites. Furthermore, the tolerance towards deactivation observed for the mesoporous HZSM-5 core was largely preserved—especially for conversion of small oxygenates like acids, alcohols and aldehydes, resulting in vapors with 14 wt% O.

Synthesis of mesoporous ZSM-5 zeolite encapsulated in an ultrathin protective shell of silicalite-1 for MTH conversion

Abstract Coke formation is a major reason in deactivation of acidic zeolite catalysts in industrial processes such as methanol to hydrocarbons conversion. Protecting the surface of acidic zeolite with an inert porous shell can greatly hinder the coke formation on the surface, and hence boost the lifetime of the catalyst. In this work, a solid-state steam-assisted method for synthesis of such optimized protective shell (silicate-1, ~15 nm thickness) is designed. This general and simple protocol can be applied to acidic zeolite catalysts to improve their catalytic lifetime. The silicalite-1 shell is synthesized on mesoporous ZSM-5 zeolite to explore its catalytic activity in methanol to hydrocarbons conversion. XPS and TEM analysis confirm the coverage of mesoporous zeolite crystals by non-acidic shell. In addition, nitrogen physisorption shows the accessibility of mesoporous ZSM-5 via microporous silicalite-1 network. Applying this protective shell increases the lifetime of the catalyst by 100% and its conversion capacity by 130%, in comparison to mesoporous ZSM-5 without the shell. The controlled formation of thin layer of microporous silicalite-1 around mesoporous ZSM-5 crystals (without growth of individual silicalite-1) accounts for enhanced catalytic improvement.

Synthesis of core–shell ZSM-5 zeolite with passivated external surface acidity by b-oriented thin silicalite-1 shell using a self-assembly process

A core–shell HZSM-5@silicalite-1 zeolite coated with a relatively continuous b-oriented thin silicalite-1 shell has been synthesized by a self-assembly method of reversing the negative surface charge of ZSM-5 crystals before the secondary hydrothermal crystallization. The growth orientation of shell crystals is confirmed by electron microscopy technology. N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscope with energy-dispersive X-ray spectrometry (STEM-EDS) measurements reveal that the core ZSM-5 crystals are coated with a relatively continuous monocrystal-thick silicalite-1 shell. The surface acidity analysis (Pyridine-FTIR and 2,4,6-collidine-FTIR) combined with the two probe chemical reactions using molecules that are either too large or adequately sized to access MFI pores has confirmed the passivation of external surface acid sites without hindering the intrinsic activity of the parent HZSM-5, which is consistent with the results from the electron microscopy and textural analysis.

Coating mesoporous ZSM-5 by thin microporous Silicalite-1 shell: Formation of core/shell structure, improved hydrothermal stability and outstanding catalytic performance

Abstract Nanostructure control is an important improvement strategy for zeolite catalyst. A novel hierarchical core/shell zeolite structure with mesoporous core and thin microporous Silicalite-1 shell was prepared by secondary coating of mesoporous ZSM-5 in this paper. The zeolite structure was proved by the combination of broad characterization techniques especially electron microscopy from different length scales. The combination of focused ion beam scanning electron microscope (FIB-SEM) and scanning transmission electron microscopy (STEM) clearly proved the formation of desired core/shell structure. The as-prepared core-shell structured hierarchical MFI (Framework Type) zeolite showed a high hydrothermal stability, unique acidic property and outstanding catalytic performance in methanol to hydrocarbon reaction and biomass catalytic pyrolysis. The synthesis strategy could be extended to other zeolites and generated a family of novel hierarchical zeolites.

Preparation and Characterization of Core–Shell Composite Zeolite BEA@MFI and Their Catalytic Properties in ESR

A group of BEA@MFI core–shell zeolite catalysts were successfully constructed with Cu-, Ni-modified Beta core and Co-based Silicalite-1 shell by combining seed induction secondary growth technique and incipient wetness impregnation method. The resulting micro-composite possess a well-defined core–shell structure with high surface area and abundant mesopore in the outer shell, and a relative large truncated bi-pyramidal shape core of Beta. It was further used to correlate their performance in ethanol steam reforming. The obtained xNiyCu-Beta@Co-Silicalite-1 catalysts exhibited excellent catalytic performance compared with the conventional zeolite catalysts. Particularly, the 2.5Ni2.5Cu-Beta@CoSilicalite-1 catalyst exhibited the highest selectivity of hydrogen, the lowest selectivity of by-products, the long-term stability and coking-resistance capability. This is mainly attributed to the excellent textural properties. And the Ni, Cu nanoparticles which incorporated into the core–shell micro-composites protected the properties of active phases effectively. Moreover, the “purification effect” of the Co-base shell is conducive to obtaining high-purity hydrogen through a multiple reaction system.

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.

From hydrophilic to hydrophobic: A promising approach to tackle high CO2 selectivity of Fe-based Fischer-Tropsch microcapsule catalysts

Zeolite supported Fischer-Tropsch (FT) catalysis has attracted extensive attentions in past few years. Capsule catalysts have unique characteristics of tuning product selectivity more precisely and enhancing stability of catalysts during reaction, which makes them to stand out of the crowed. Fe-based FT catalysts have been facing limitations for syngas conversion to hydrocarbons with their associated problems of high CO2 selectivity and rapid catalyst deactivation. A series of ZSM-5 supported Fe-based microcapsule catalysts, composed of Fe/ZSM-5 core and silicalite-1 shell, was prepared and employed for direct synthesis of gasoline range hydrocarbons from syngas. Tuning silicalite-1 shell thickness significantly affected water-gas shift reaction with increasing hydrophobicity of catalyst surface, and greatly decreased CO2 selectivity. The microcapsule catalysts significantly suppressed the CO2 selectivity as compared with supported Fe-based catalyst. Moreover, all zeolite supported Fe-based catalysts, showed significantly high gasoline range hydrocarbons selectivity (about 60%). The proposed catalyst design suggests a promising approach to overcome high CO2 selectivity challenge associated with Fe-based FT catalysts.

High Water Tolerance of a Core-Shell-Structured Zeolite for CO2 Adsorptive Separation under Wet Conditions.

Dehumidification in CO2 adsorptive separation processes is an important issue, owing to its high energy consumption. However, available adsorbents such as low-silica zeolites show a significant decrease in CO2 adsorption capacity when water vapor is present. A core-shell-structured MFI-type zeolite with a hydrophilic ZSM-5 coated with a hydrophobic silicalite-1 shell layer was applied in CO2 adsorptive separation under wet conditions. This hybrid material demonstrated remarkably high water tolerance with stable CO2 adsorption performance without additional thermal treatment for regeneration, whereas a significant decrease in the CO2 adsorption amount because of water vapor was observed on the parent ZSM-5. The core-shell structure of zeolites with high pore volumes, such as LTA or CHA, could also be suitable candidates for high CO2 adsorption capacity and high water tolerance for practical applications.

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.

Complete encapsulation of zeolite supported Co based core with silicalite-1 shell to achieve high gasoline selectivity in Fischer-Tropsch synthesis

Zeolite-based capsule catalysts have exhibited significant results in terms of catalytic activity and product selectivity in Fisher-Tropsch synthesis. Herein, we synthesized a ZSM-5 supported Co based microcapsule catalyst encapsulated by microporous silicalite-1 shell via hydrothermal synthesis process. Synthesized microcapsule catalyst has a uniform microporous structure with an additional stay zone for both reactants as well as product inside its channels and showed significantly high CO conversion rate (68.9%) and gasoline range hydrocarbon selectivity (74.7%) with a low CO2 and CH4 selectivity (2.8% and 8.7%, respectively). This microcapsule catalyst may consider to be used on commercial scale because of its facile preparation method and promising performance.

Synthesis and application of HZSM-5@silicalite-1 core–shell composites for the generation of light olefins from CH3Br

To improve activity and hinder deactivation, nonacidic polycrystalline silicalite-1 was contiguously coated on HZSM-5 to yield HZSM-5@silicalite-1 composites using a hydrothermal synthesis method. The obtained samples were examined as catalysts for the generation of light olefins (ethylene and propylene) from CH3Br, and found to show high catalytic activity, stability and high selectivity to the desired products. The excellent performance is attributed to the silicalite-1 shell which causes passivation of acid sites on the external surface of HZSM-5. It was observed that the HZSM-5@silicalite-1 composite with thicker coating (ZS-2) shows much higher stability and selectivity to light olefins (up to 80%) than that with thinner coating (ZS-1), indicating that the surface of HZSM-5 crystals of the latter was less covered. Based on the characterization results, it is deduced that the catalytic stability of ZS-2 is due to the silicalite-1 shell that hinders HZSM-5 from deactivation as a result of surface coking.

Zeolitic Core@Shell Adsorbents for the Selective Removal of Free Glycerol from Crude Biodiesel

Selective adsorption of free glycerol from crude biodiesel was investigated by using mesoporous silica spheres coated with a thin shell of microporous silicalite-1. A polycrystalline silicalite-1 shell was formed upon first covering the external surfaces of various core templates with discrete silicalite-1 nanocrystals, and this was followed by short hydrothermal treatment to ensure shell uniformity. Batch glycerol adsorption experiments were conducted to evaluate the ability of the sorbents to remove free glycerol selectively from crude biodiesel mixtures at various temperatures, also in comparison to that of conventional sorbents, for example, bare mesoporous silica gel spheres and zeolites. The silicalite-1 shell provided a microporous membrane that hindered the diffusion of fatty acid methyl esters into the mesopores of the composite sorbent, whereas the large pore volume of the mesoporous core enabled multilayer glycerol adsorption; this ultimately substantially enhanced the performance in terms of purification yield and adsorption capacity.

Manufacture of b-Oriented ZSM-5/Silicalite-1 Core/Shell Structured Zeolite Catalyst

A b-oriented MFI shell was formed on the ZSM-5 crystal by pretreating the core using ammonia prior to the hydrothermal synthesis in tetrapropyl ammonium hydroxide medium. The effect of surface structure of the core material on synthesis of MFI/MFI zeolite was investigated. The surface Si-OH groups and amorphous aluminate may play an important role in forming the b-oriented coating. The shell composition changed from high-silica ZSM-5 to silicalite-1 after twice coating synthesis, while the shell coverage increased from 85% to 99%. In toluene methylation, the silicalite-1 shell not only prevented the deactivation of the catalyst, but also enhanced para-selectivity up to 61%.