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In this work, composite catalytic systems of natural mordenite and synthetic MFI-type zeolite containing Pd and Ni nanoparticles (0.5–1.5% by weight in total) were prepared by mechanical mixing (1:1), optionally with the addition of α- or γ-Al2O3 as a binder. The samples were examined using IR spectroscopy, X-ray diffractometry, transmission electron microscopy, low-temperature nitrogen ad(de)sorption, and tested in the model reaction of n-hexane hydroisomerization in a micro-pulse mode to determine the effect of composition on the peculiarities of linear alkane transformation. It has been shown that in the obtained catalytic systems, modifications of aluminum oxide used as a binder affect the effectiveness of catalysts in the conversion of n-hexane. This is explained by the different dispersity of α- and γ-Al2O3 particles, which causes differences in the characteristics of the porous structure of the obtained composites and, in turn, different accessibility of their active sites. In this respect, α-Al2O3 proved to be better than γ-Al2O3. The highest effectiveness in the formation of hexane isomers in general, as well as dimethyl branched isomers, was demonstrated by the sample possess the maximum concentration of Brønsted acid sites and the highest Brønsted/Lewis ratio. Synergy between the two zeolite components in the formation of isomers has been found out, which was more effective in samples with an isotropic distribution of zeolite phases. The synergetic effect is explained by the productive mutual influence of metal phases included in the zeolite. [ABSTRACT FROM AUTHOR]

Macro-microporous silicate-1 zeolites(MFI crystalline form) were synthesized via the "dissolution-recrystallization process", utilizing monodisperse silica spheres (500 nm) as the silica source and macroporous templates, as well as tetrapropylammonium hydroxide as the microporous template, to enable in-situ formation of the macropores. The samples displayed macropore diameters ranging between 150 ~ 350 nm, a specific surface area of 350 m²/g, and a total pore volume of 0.24 cm³/g. The influence of synthetic conditions, such as crystal time, the addition of ethanol, the drying method, the amount of structure directing agent and the size of silica spheres, on the introduction of macropores was revealed. On this basis, macroporous ZSM-5 zeolites were further successfully synthesized with aluminum atoms incorporated into the pure silica zeolite framework. [ABSTRACT FROM AUTHOR]

As an MFI-type zeolite, ZSM-5 zeolite has wide applications in industry, such as in the fine chemical, petrochemical, and coal chemical industries. However, shape control of ZSM-5 nanocrystals constitutes one of the major challenges of current nanotechnology. Here, the MFI framework structure was used as the theoretical model of pure silicon ZSM-5 to investigate the surface energy and Wulff shape. The models with different crystal surfaces were simulated by molecular dynamics (MD) with the assistance of machine learning potentials (MLPs). The factors influencing the crystal surface energy, such as temperature, pH, and ionic concentration, have been studied in detail. Depending on the calculated surface energies, the crystal surface morphology and its ratio were obtained by means of the Wulff theorem. The results show that the area in the equilibrium shape of the (110) surface is usually the largest, and its proportion varies with external conditions. A high temperature and high concentration of the aluminum source promoted the growth of the (110) crystal surface, and the theoretical value of the crystal surface ratio was as high as 90%. This study provides theoretical insight into the synthesis of zeolites with different morphologies of all-silicon or low-aluminum. [ABSTRACT FROM AUTHOR]

As an MFI-type zeolite, ZSM-5 zeolite has wide applications in industry, such as in the fine chemical, petrochemical, and coal chemical industries. However, shape control of ZSM-5 nanocrystals constitutes one of the major challenges of current nanotechnology. Here, the MFI framework structure was used as the theoretical model of pure silicon ZSM-5 to investigate the surface energy and Wulff shape. The models with different crystal surfaces were simulated by molecular dynamics (MD) with the assistance of machine learning potentials (MLPs). The factors influencing the crystal surface energy, such as temperature, pH, and ionic concentration, have been studied in detail. Depending on the calculated surface energies, the crystal surface morphology and its ratio were obtained by means of the Wulff theorem. The results show that the area in the equilibrium shape of the (110) surface is usually the largest, and its proportion varies with external conditions. A high temperature and high concentration of the aluminum source promoted the growth of the (110) crystal surface, and the theoretical value of the crystal surface ratio was as high as 90%. This study provides theoretical insight into the synthesis of zeolites with different morphologies of all-silicon or low-aluminum.

In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40–68%. In case of desilicated zeolites, at 270–290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a “1” diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature.It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of “swiss cheese”. Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M−10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M−10c).The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210 °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230 °C, 250 oC and 270 °C.

• Formation of phenols via gas-phase oxidation of benzene. • Copper-loaded MFI zeolite compacts prepared via a binderless synthetic method. • Formation of zeolites with specific surface area and crystallinity. • One-step benzene gas-phase oxidation reaction using zeolites as catalysts. Phenols are essential raw materials for various fields, and several studies have focused on their synthesis. The development of an efficient one-step synthetic method for the industrial production of phenols is highly important in terms of cost, energy, and environmental impact. In this study, we investigated the formation of phenols via the gas-phase oxidation of benzene using copper-loaded MFI zeolite compacts prepared via a binderless zeolite synthetic method. The catalytic activity of the zeolite in the gas-phase phenol one-step synthetic reaction was investigated, in addition to the effect of benzene diffusion in the molded zeolite and the reaction due to water vapor addition to the reaction gas. The results showed that the activity of the copper-loaded MFI zeolite compacts was almost equivalent to that of powdered copper-loaded MFI zeolites. An effect of diffusion was observed on the external boundary film diffusion where the linear velocity was low. However, no effect of diffusion or internal diffusion was observed in the area where the linear velocity was high. Furthermore, the addition of water vapor to the reaction gas suppressed the decrease in phenol formation activity due to the formation of coke on the catalyst surface. [Display omitted] [ABSTRACT FROM AUTHOR]

• Trace amount of CH 3 SH deteriorated C 2 H 4 aromatization over zeolite catalyst. • Ga modification on MFI-type zeolite improved stability of C 2 H 4 aromatization. • Ga modification controlled the surface acidity which led to catalyst stability. To develop a new CO 2 utilization process from sulfur-containing gases, such as sour gas and biogas, we investigated the influence of trace amounts of sulfur gas, namely hydrogen sulfide and methanethiol (CH 3 SH), on ethylene aromatization over an MFI-type zeolite catalyst. The protonated MFI-type zeolite showed high activity and stability for ethylene aromatization; however, its activity rapidly deteriorated in the presence of trace amounts of CH 3 SH. To improve the catalytic activity, zeolite was modified with Ni, Cu, Zn, and Ga. Although modifications with Ni, Cu and Zn did not improve the catalytic activity for ethylene aromatization, Ga modification contributed to the stability of ethylene aromatization in the presence of trace amounts of CH 3 SH. Characterization of the as-made catalysts indicated that Ga modification not only weakened the surface acidity of the zeolite but also endowed the catalyst with dehydrogenation capability. These properties suppressed CH 3 SH decomposition on the acid site, leading to stable catalytic performance for ethylene aromatization in the presence of trace amounts of sulfur gas. [ABSTRACT FROM AUTHOR]

The effect of the void between filler (MFI-type zeolite) and matrix (a polymer of intrinsic microporosity) in the mixed matrix membrane (MMM) on CO 2 /CH 4 gas permeability was investigated at the atomistic scale by non-equilibrium molecular dynamics (NEMD). In our NEMD, the permeation through the void at the interface between the filler and the matrix, the matrix, and the filler were simulated simultaneously. The permeating path was analyzed to clarify the void effect at the interface between the matrix and the filler on permeance and selectivity. NEMD results clearly showed that permeation through the filler and matrix was the fastest that could be expected using the MMM design concept. Furthermore, permeation through the void also showed high CO 2 selectivity, although the permeation rate was lower than that through the filler inside and the matrix. The CO 2 permeation through the filler and matrix was dominant at about 43% of the total permeance, whereas the permeation through the void was about 40% of the total permeance. This means that the void at the interface significantly influenced the permeability and selectivity. This suggests that controlling the void structure/affinity between the filler and the matrix could drastically improve MMM permeation properties. [Display omitted] • The mixture gas permeation through the interface between matrix (PIM-1) and filler (MFI type zeolite) in MMM are investigated and demonstrated by non-equilibrium molecular dynamics (NEMD). • Our NEMD results showed that the addition of MFI zeolite filler to PIM-1 membrane in a uniform arrangement suppresses the swelling of matrix, and these MMMs exhibit higher CO 2 selectivity under high CO 2 partial pressure. • The interface between PIM-1 and MFI zeolite showed CO 2 selectivity comparable to that of the MFI filler, more than 80% of CO 2 molecules permeated through the filler inside and the void at the interface. [ABSTRACT FROM AUTHOR]

A membrane for controlling methanol-to-olefin (MTO) reactions was developed, which featured an MFI-type zeolite membrane (Si/Al = 25) that was synthesized on a porous α-alumina substrate using a secondary growth method. Here, the H2/SF6 permeance ratios were between 150 and 450. The methanol conversion rate was 70% with 38% ethylene selectivity and 28% propylene selectivity as determined using a cross-flow membrane contactor. In order to improve the olefin selectivity of the membrane, the MFI zeolite layer (Si/Al = ∞) was coated on an MFI-type zeolite membrane (Si/Al = 25). Using this two-layered membrane system, the olefin selectivity value increased to 85%; this was 19% higher than the value obtained during the single-layer membrane system.

The impact of the organic species in the synthetic gel of ZSM-5 on the distribution of Al atoms in the MFI framework and catalytic performance was investigated; ZSM-5 zeolites were synthesized by exclusively using TPAOH, and Na cations with PET to elucidate how the distribution of Al atoms is governed by the types of organic species in the synthetic gel. The distribution of Al atoms was investigated by 27 Al MAS NMR technique and constrain index (CI). Catalytic cracking of 1-octene over the ZSM-5 catalysts was carried out to estimate “hydrogen transfer coefficient (HTC) and cracking mechanism ratio (CMR) values”. We found that HTC and CMR values are dependent on the distribution of Al atoms. The fine-control of Al distribution in the MFI structure could improve the tolerance for coke deposition in 1-octene cracking. [ABSTRACT FROM AUTHOR]

Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different Si/Al ratios H-MFI-type zeolites were prepared using the emulsion method. • p-propylphenol/benzene transalkylation over H-MFI-type zeolite in SCF. • Kinetics of transalkylation of p-propylphenol/benzene were evaluated. • Successful reduction of internal diffusion limitations and increased selectivity. • Reaction limiting conditions for crystal size below 125 nm (Si/Al = 95.0). The transalkylation reaction kinetics of 4-propylphenol (ppp) and supercritical benzene (11.0 MPa) over H-MFI-type zeolites, using different particle size and Si/Al ratios, in the temperature range of 623 K – 673 K, was studied in a fixed bed reactor. A 1st order parallel reaction kinetic model was evaluated for transalkylation of ppp and benzene, and ppp isomerization. High conversion of ppp and phenol production with low coke formation was obtained with nanometer-sized particles, transalkylation reaction proceeded under reaction control conditions. Thiele modulus was calculated to evaluate internal diffusion limitations, clearly observed when increasing the particle size (activation energies over micrometer- and nanometer- sized particles, 60.0 and 120 kJ mol−1, respectively). Nonetheless, decreasing the particle size (2.00 × 103 to 100 nm) successfully reduced the internal diffusion limitations and increased the selectivity of the reaction. The study showed that increasing Al sites in the framework not only increases the specific constant rate of the reaction, but also its selectivity, with a low impact on the effectiveness of the reaction according to the Thiele Modulus equation and the particle size obtained. [ABSTRACT FROM AUTHOR]

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste.

A new one step approach for the preparation of MFI-type zeolites through direct trans-formation of pre-modified diatomite is reported. Two diatomite species modified by calcination and acid treatment were used as silica and alumina sources. The progress of the transformation was investigated by analyzing samples after different crystallization times at 453 K. Tetrapropylammonium hydroxide was utilized for the first time as bi-functional molecule for silica dissolution in diatomite and structure directing agent during zeolite formation. In this way, the use of an additional alkaline source, such as sodium hydroxide, for silica dissolution was not necessary. The applied diatomite samples contained amorphous silica in combination with impurities like feldspar, anatase and quartz. This allowed the systematic investigation of the influence of modification procedure, amorphous silica content and crystalline impurities of the different diatomite samples on the direct transformation in MFI-type zeolites. During the transformation process, the feldspar was totally dissolved. The quartz content was reduced to <10 wt% in the final products as compared with the modified diatomite starting material. X-ray diffraction, nitrogen adsorption, scanning electron microscopy and optical emission spectroscopy were used to characterize these materials. [ABSTRACT FROM AUTHOR]

Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy.

Diffusivity and adsorption properties of n -hexane within coked MFI-type zeolites, the micropore volume, and number of acid sites were measured to investigate the deactivation mechanism of MFI-type zeolite during n -hexane cracking. The coked MFI-type zeolite was prepared by n -hexane cracking over the zeolite at 923 K. The diffusivity and adsorption isotherm of n -hexane within the coked zeolite was obtained using the constant volume method. Micropore volume and acid sites number of the coked zeolite decreased with increasing coke loading, resulting in a decrease in n -hexane adsorption on the coked zeolite. In contrast, intracrystalline diffusivity of n -hexane within the coked zeolite increased with coke loading, and effective diffusivity remained constant regardless of coke loading. Coke formation on the acid site inside the zeolite pores caused a decrease in n -hexane adsorption onto the acid site, resulting in geometrical limitations that promoted the major mass transfer resistance. Effect of diffusivity on MFI-type zeolite deactivation during n -hexane cracking was small. The main cause of the deactivation was considered to be a decrease in reaction rate due to the decrease in the number of acid sites for n -hexane cracking by coke formation. [ABSTRACT FROM AUTHOR]

Hierarchically porous diatomite/MFI-type zeolite composites were prepared by transforming the natural diatomaceous silica into MFI-type zeolite by a vapor-phase transport method, followed by a desilication treatment. The morphology and macroporosity of the diatomite were well preserved in the parent diatomite/MFI-type zeolite composite (Dt/Z). Treatment of Dt/Z by desilication in aqueous 0.2 M NaOH solution at 60 °C for 1 h resulted in a mesopore size distribution centered at approximately 7 nm, without significantly altering the macroporosity and microporosity of the resulting composite. Further desilication treatment (10 h) broadened the mesopore size distribution, whereas the macropores sourced from the diatomite support were significantly damaged and a fraction of the micropores was narrowed to approximately 0.49 nm. Under the optimal desilication condition (1 h), the desilication-treated Dt/Z sample (Dt/Z-A 1h ) exhibited a higher adsorption capacity, better affinity, and faster adsorption kinetics toward benzene than the parent Dt/Z, as evaluated via a gravimetric method using an Intelligent Gravimetric Analyzer. The excellent benzene adsorption performance of Dt/Z-A 1h was attributed both to the increase in porosity and the formation of terminal silanol groups on the surface of newly developed pores after the desilication treatment. [ABSTRACT FROM AUTHOR]

Hierarchically porous diatomite/MFI-type zeolite (Dt/Z) composites with excellent benzene adsorption performance were prepared. The hierarchical porosity was generated from the microporous zeolite coated at the surface of diatom frustules and from the macroporous diatomite support. A facile NaOH etching method was employed for the first time to treat the frustule support, followed by hydrothermal growth of MFI-type zeolite at the surface of frustules previously seeded with nanocrystalline silicalite-1 (Sil-1). NaOH etching enlarged the pores on diatom frustules and further increased the coated zeolite contents ( W z ). The central macropore size of the diatom frustules increased from approximately 200–500 nm to 400–1000 nm after NaOH etching. The W z could reach 61.2%, while the macroporosity of the composites was largely preserved due to more voids for zeolite coating being formed by NaOH etching. The Dt/Z composites exhibited higher benzene adsorption capacity per unit mass of zeolite and less mass transfer resistance than Sil-1, evaluated via a method of breakthrough curves. These results demonstrate that etching of a diatomite support is a facile but crucial process for the preparation of Dt/Z composites, enabling the resulting composites to become promising candidates for uses in volatile organic compounds emission control. [ABSTRACT FROM AUTHOR]

The entrance and diffusion pathway of CO2 and dimethyl ether (DME) in MFI-type zeolite channels were investigated by a selective sealing method using large silicalite-1 crystals. The MFI-type zeolite has two kinds of orthogonal channels: straight channels and sinusoidal channels. The mouths of the straight channels are on (010) crystal faces, while those of the sinusoidal channels are on (100) faces. The channel mouths are directly sealed by silicone resin on the (100) and (010) faces so as to restrict the entrance and diffusion pathways to straight and sinusoidal channel pathways, respectively. The locations and loadings of the guest CO2 and DME molecules are determined by single-crystal X-ray diffraction structural analysis. The loadings show the difference of the adsorption rates between the pathways. The straight channel pathway is 4.2 times faster than the sinusoidal channel pathway for the CO2, and the sinusoidal channel pathway is 5.1 times faster than the straight channel pathway for the DME. It reveals their dominant pathways and the anisotropy of adsorption. The dominant pathway correlates to the stability of the channel as adsorption sites. [ABSTRACT FROM AUTHOR]

The adsorption structures of dimethyl ether (DME) on silicalite-1 zeolite (MFI-type) are determined using single-crystal X-ray diffraction. The structure of low-loaded DME-silicalite-1 indicates that all DME molecules are located in the sinusoidal channel, which is the most stable sorption site based on the van der Waals interaction between DME and the framework. The configuration of guest molecules (linear or bent) plays an important role in determining where the stable sorption site is in the pore system of MFI-type zeolites. Bent molecules favor the sinusoidal channel, while linear molecules favor the straight channel. The contribution of DME-DME interactions is considerable in the high-loaded DME-silicalite-1 structure. [ABSTRACT FROM AUTHOR]

The use of pentaerythritol in combination with the Na cation in the synthesis of ZSM-5 led to a unique Al distribution in the MFI framework; Al atoms were preferentially located at straight and sinusoidal channels, not the intersection. [ABSTRACT FROM AUTHOR]

Abstract: The energetic performance of different “Silicalite-1 – aqueous medium” systems was evaluated under high pressure. Depending on the nature of the aqueous medium, high intrusion and extrusion pressures and therefore stored and restored energies are observed. Thus, compared to the “Silicalite-1 – water” system, the stored energy is tripled in the case of “Silicalite-1 – LiCl, 3H2O” system. [Copyright &y& Elsevier]

Highlights: [•] Separation of tetramethyl ammonium hydroxide (TMAH) was investigated. [•] MFI-type zeolite powder possesses high adsorption ability for TMAH. [•] MFI-type zeolite-coated membrane was employed for nanofiltration of TMAH. [•] Nanofiltration is achieved by both molecular sieve and adsorption mechanism. [•] The membrane can be reused for nanofiltration with backwashing between cycles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Kinetic studies in thermal and catalytic cracking of n-hexane were conducted. [•] Thiele modulus was used to evaluate the crystal size to achieve reaction-control condition. [•] Nano-sized MFI-type zeolite could achieve reaction-control condition for n-hexane cracking. [Copyright &y& Elsevier]

Abstract: Kinetic analysis of burning regeneration of coked MFI-type zeolite obtained by catalytic cracking of n-hexane was studied using a multiple-reaction model. Hydrogen contained in the coke was oxidized faster than carbon, and subsequently carbon remaining after the hydrogen combustion was gradually oxidized. Reaction rates of carbon and hydrogen correlated with the Arrhenius equation; and activation energies for the combustion of carbon and hydrogen were 156kJ/mol and 140kJ/mol, respectively, regardless of the coke loading. Regeneration of coked MFI-type zeolite in the fixed-bed reactor was simulated numerically using reaction rates obtained from the kinetic analysis. The numerical result for changes in gas composition with time at the reactor outlet agreed well with the experimental results. Axial distribution of the temperature and concentration of water vapor in the catalyst bed was obtained numerically and results showed that the temperature and water vapor near the outlet were higher than other location in the reactor. [Copyright &y& Elsevier]

Abstract: MFI zeolite membranes were synthesized on α-alumina substrates by in situ hydrothermal crystallization. The separation of p-/o-xylene (PX/OX) mixtures was performed to evaluate the quality of MFI zeolite membranes. EDS analysis showed that aluminum from the substrate was incorporated into the zeolite structure during membrane synthesis. The negatively charged aluminosilicate framework possessed ion-exchange properties due to the presence of charge-balancing cations, which could produce acidic sites for xylene isomerization. A membrane with a PX permeance of 2.58×10−8 mol/m2 sPa and a PX/OX separation factor of 19.3 at 300°C was modified by H+ ion-exchange treatment and used for the isomerization of m-xylene (MX). The effects of the operating temperature, feed flow rate and sweep flow rate on the membrane reaction were investigated. For MX isomerization, a high PX selectivity of 92.1% and a MX conversion of 6.5% were achieved at 270°C over the catalytic membrane. [Copyright &y& Elsevier]

A series of metal containing MFI-type zeolites were synthesized by the rapid crystallization method with in two hours. Al(III), Cr(III), Cu (II), and Fe(III) metal ions were incorporated in the structure. Pure siliceous (Al free) MFI structured zeolite was also prepared by the same procedure as used for the metallosilicate synthesis. Si/M ratio of the synthesis gel was 100 for metallosilicates aiming for high-silica zeolites. The products have been characterized by elemental analysis, specific surface area determination, scanning electron microscopy with EDX analysis, electron spin resonance, and thermal analysis. Catalytic property of the zeolites was measured for methanol to olefin conversion reaction. The results of XRD measurement showed the only crystalline phase present was that of MFI-type zeolite. E.s.r spectroscopy has been used to study the isomorphic substitution of the metal ions incorporated in the structure. The results show that Fe(III) and Cu (II) were mainly incorporated while, Cr(III) was observed to be present in non-framework sites. The amount of template occluded into the structure was determined by thermal analysis and found to be the same for metallosilicates and highly crystalline aluminum free zeolite. The results of catalytic activity showed that about 85% selectivity (based on gaseous hydrocarbon) for C-C olefin was achieved in the case of iron containing synthesized high-silica zeolite as compared with 58% in the case of Al-containing zeolite catalyst. [ABSTRACT FROM AUTHOR]

Abstract: A cationic organosiloxane compound where two tetrapropylammonium (TPA) cations are bridged by a tetramethyldisiloxane unit (MSi-TPA) has been used as a structure-directing agent (SDA) for the synthesis of a pure silica MFI-type zeolite, silicalite-1, with a unique microstructure and particle morphology. The hydrothermal treatment of the mixture of tetraethoxysilane as a silica source, MSi-TPAOH, and water yields solid products that are identified as silicalite-1 by X-ray diffraction and solid-state 29Si MAS NMR. Solid-state 29Si and 13C CP/MAS NMR and elemental analyses confirm that MSi-TPA is covalently incorporated in the MFI framework via cleavage of the disiloxane linkage. Compared with conventional silicalite-1 prepared with TPA cations, the amount of defect sites is higher, which can be attributed to the attachment of the organosilyl groups to the framework by Si–O–Si bonds. Scanning electron microscopic (SEM) observation shows spherical particle morphology that is quite different from the typical coffin-shaped crystals obtained with TPA. Importantly, MFI is not formed when triethoxysilyl- and diethoxysilyl-TPAs, instead of MSi-TPA, are used as SDAs under similar conditions, suggesting that the possible number of Si–O–Si linkages formed by SDAs greatly affects the crystallization process of MFI zeolite. [ABSTRACT FROM AUTHOR]

id treated silica fibers, coming either from asbestos cord waste or calcium aluminosilicate glass, were engaged as reactants to product MFI type zeolite fibers applying a dry gel conversion (DGC) type synthesis. The impact of amorphous silica fiber shape and synthesis conditions on morphology of the final product was investigated. Enhanced zeolite nucleation and restricted crystal growth are necessary to maintain the initial fiber morphology. Whereas a DGC type crystallization in hydroxide media results in the formation of zeolite fibers, the use of fluoride ions leads to the formation of large individual zeolite particles. Synthesis conditions have to be adapted to form zeolite particles with an average size smaller than the silica fiber diameter to allow a good conservation of the fiber morphology. Final zeolite fibers have textural properties comparable to a standard zeolite product and are promising for adsorption applications. [ABSTRACT FROM AUTHOR]

MFI-type zeolite membranes were hydrothermally synthesized as a thin layer on macroporous α-alumina discs coated with 1µm MFI-type seed crystals as seed. The effect of soda (Na2O) concentration on the morphology of the membranes was investigated. Soda concentration, and thus the hydroxyl ion concentration, was changed between 0.25 and 6.5 mol/mol gel. At low soda concentrations the crystals forming the layer exhibited mostly (h0h)/c-axis orientation, but at high soda concentrations a membrane layer formed from randomly oriented crystals. The membranes showed high H2/n-butane ideal selectivity of 476 and 36 at 25°C and 150°C, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A new method is proposed for measuring the diffusivities of hydrocarbons within solid catalysts in the liquid phase using Raman spectroscopy. This method was applied to measuring the intracrystalline diffusivity of benzene within silicalite-1 (SL) and γ-Al2O3 in cyclohexane solution at a temperature range from 323 to 413K. From Raman spectra of benzene/cyclohexane solution, the proportional relationship between the benzene concentration and the intensity ratio of benzene to cyclohexane was obtained, which enables us to measure the benzene concentration in the solution. From this relationship, the transient change in benzene concentrations in the solution due to its adsorption and diffusion within the catalysts can be measured. The intracrystalline diffusivity (D ad) in the liquid phase was calculated using theoretical equations, and the experimental results of the concentration change with time. The Arrhenius plots of the diffusivity of benzene within SL (micro pore region) in the gas and liquid phase were correlated with a single line, regardless of the existence of solvent in the liquid phase. This result indicates that in the structure-sensitive diffusion region (diffusion of benzene within the micropore of SL), the diffusion mechanism in the gas phase is the same as that in the liquid phase. In contrast, the diffusivity of benzene within macro-pores of γ-Al2O3 in the liquid phase was approximately 107 times higher than that within SL. The diffusivity of benzene within γ-Al2O3 was almost the same as that of the theoretical molecular diffusion coefficient in cyclohexane solution calculated from the Wilke–Chang equation. [Copyright &y& Elsevier]

Abstract: Hydrophilic silicalite-1 nanocrystal-layered membrane was successfully prepared on an alumina ceramic filter. The silicalite-1 nanocrystals were layered on the outer surface of cylindrical alumina ceramic filters, followed by a hydrothermal synthesis to form a silicalite-1 layer (protection layer) on the nanocrystal layer. In order to achieve high hydrophilic properties of the membrane with the remaining silanol group, the liquid phase oxidation technique was applied to remove the template. From the SEM observation, the nanocrystal layer and the protection layer were clearly observed, and the silicalite-1 protection layer was uniformly formed on the nanocrystal-layer. Pervaporation experiments to separate water from water–acetone solution (acetone: 90wt%) were conducted using the silicalite-1 nanocrystal-layered membrane. The membrane exhibited the selective permeation as well as the high flux of water. In the nanocrystal-layered membrane, water–silanol networks were formed on the non-zeolitic pores surface among the nanocrystals, which were the main channels for water permeation. The increase in the number of pores among the silicalite-1 crystals leads to a high flux of water through the membrane. [Copyright &y& Elsevier]

Abstract: MFI-type zeolite particles of 0.1–1μm in diameter were prepared by adjusting tetra-n-propylammonium hydroxide (TPAOH) and water contents in synthesis mixtures. Using those particles as seeds, MFI-type zeolite membranes were prepared on the surface of a porous mullite tube by secondary growth. The membranes were formed as polycrystalline zeolite layers on and inside the porous support, and the membranes were composed of the [h 0 h]-oriented crystallites. The membrane consisting of a-oriented crystallites could be also prepared. However, the a-oriented zeolite layers were not active on the permeation properties of butanes. Rather the size and loaded amount of the seed particles influenced on the permeation properties through the membranes. As a result, the n-C4H10/i-C4H10 permselectivity could be increased to 220 by adjusting the size and the loaded amount of particles. These results suggest that the number of loaded particles affects on the permeation properties through the membranes. [Copyright &y& Elsevier]

Abstract: Biomorphic self-supporting MFI-type zeolite frameworks with hierarchical porosity and complex architecture were prepared using a 2-step (in-situ seeding and secondary crystal growth) hydrothermal synthesis in the presence of a biological template (Luffa sponge), employed as a macroscale sacrificial structure builder. The bio-inspired zeolitic replica inherited the complex spongy morphology and the intricate open-porous architecture of the biotemplate. Moreover, it exhibited reasonable mechanical stability in order to study the applicability of the biomorphic catalyst in a technical catalytic process. A bio-inspired catalytic reactor utilising the self-supporting ZSM-5 scaffold in monolithic configuration was developed in order to test the catalytic performance of the material. [Copyright &y& Elsevier]

Preferentially oriented and continuous B–Al–ZSM-5 zeolite membranes have been prepared from B-containing porous glass disks in a mixed vapor of ethylenediamine, tri-n-propylamine and H2O. The crystals with the orientations of {101}/{011} and (002) planes paralleling to the substrate surfaces predominate in the membranes. The membranes are about 60μm in thickness. On the calcined zeolite membranes, the ideal selectivity of H2, He, Ne, Ar, O2 and CO2 over N2 is 16.8, 15.5, 12.6, 9.4, 8.6 and 5.3, respectively. The ideal selectivity of CO and SO2 over N2 is 0.13 and 0.018, respectively. The ideal selectivities of O2 over CO and SO2 reach 65 and 491, respectively. The highest water separation factors appearing at 303 K are 28, 136 and 519 for the solutions of 5wt.% EtOH/H2O, 50wt.% EtOH/H2O and 95wt.% EtOH/H2O at different temperatures, respectively, indicating that the prepared membranes are strongly hydrophilic. [Copyright &y& Elsevier]

Layers of b-oriented silicalite crystals formed on alumina substrates were characterized by SEM and AFM. At short synthesis times, small 10–40 nm nuclei were found on the surfaces of the alumina particles of the support and also on the faces of well developed silicalite crystals. After a certain period of time, these nuclei are dissolved or incorporated into the growing crystals and only crystal growth can be observed. Large silicalite crystals (up to 3 mm in size) were also synthesized as a way to obtain a silicalite standard. The nanostructure of the nuclei above mentioned revealed by AFM was in agreement with that of a well growth large silicalite crystal. [Copyright &y& Elsevier]

Macroporous glass beads (Na2O–B2O3–SiO2) with a particle diameter of ∼300 μm and an average pore diameter of 92 nm, obtained by the VYCOR-process, were transformed into MFI-type containing beads, that retained the original shape. The conversion was achieved through a hydrothermal treatment with an aqueous mixture of an Al-source (sodium aluminate or aluminum sulfate) and a template (tetrapropylammonium bromide (TPABr) or dipropylamine (DPA)). The resulting products were characterized by X-ray diffraction, 11B MAS NMR, N2-adsoption and SEM. The filtrates were analyzed by ICP-OES. Using two different templates and two kinds of Al-source MFI-type beads with varying properties were obtained. The boron atoms, which are constituents of the glass material, were used as probe atoms for the characterization of the synthesis procedure. With DPA the crystallization took place inside and on the outer surface of the spheres, while TPABr led to a shell like crystallization starting from the outer surface of the glass particles. The type of Al-source influences the pH value of the reaction mixture and varies the Si/B ratio in the obtained products. [Copyright &y& Elsevier]

[Display omitted] • Ultrasonic irradiation of zeolites enhances Si and Al extraction. • Ultrasounds improves mesoporosity of prepared zeolites. • Ultrasonic desilication changes neither the crystallinity nor morphology. • Ultrasonic desilication improves catalytic properties of MFI-type zeolites. In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40–68%. In case of desilicated zeolites, at 270–290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a "1" diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature. It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of "swiss cheese". Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M−10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M−10c). The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210 °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230 °C, 250 oC and 270 °C. [ABSTRACT FROM AUTHOR]

The intracrystalline diffusivity of phenolic compounds (phenol, p -propylphenol and m -cresol) and toluene within silicalite-1 and MFI-type zeolite with Si/Al = 303 (H-MFI) in the liquid phase (solvent: mesitylene) in the temperature range from 313 to 353 K were measured by using the constant volumetric method. The amounts of phenol, p -propylphenol, and toluene adsorbed onto silicalite-1 at 313, 323 and 353 K were approximately the same, whereas less m -cresol was adsorbed because of its larger kinetic diameter. Unlike adsorbed toluene, adsorbed of phenol displayed stronger interactions in H-MFI than in silicalite-1, indicating that hydrogen bonding between the OH group of phenol and Brønsted acid sites in H-MFI enhanced the adsorption of phenol. Whereas the intracrystalline diffusivity of phenol, p -propylphenol, and toluene within silicalite-1 are approximately the same, m -cresol exhibited lower intracrystalline diffusivity, indicating that the intracrystalline diffusivity was governed by geometrical limitation. The intracrystalline diffusivity of phenol was lower within H-MFI with acid sites than within silicalite-1. The residence time of phenol on the acid sites became longer than that of toluene, which led to a difference in the intracrystalline diffusivity between phenol and toluene within H-MFI. [Display omitted] ● Diffusion of phenolic compounds within MFI-type zeolite was measured. ● Diffusivity of phenolic compounds in slicalite-1 depends on their kinetic diameter. ● Hydroxy group in phenols strongly adsorbed on acid site effect their diffusivity. [ABSTRACT FROM AUTHOR]

A membrane for controlling methanol-to-olefin (MTO) reactions was developed, which featured an MFI-type zeolite membrane (Si/Al = 25) that was synthesized on a porous α-alumina substrate using a secondary growth method. Here, the H2/SF6 permeance ratios were between 150 and 450. The methanol conversion rate was 70% with 38% ethylene selectivity and 28% propylene selectivity as determined using a cross-flow membrane contactor. In order to improve the olefin selectivity of the membrane, the MFI zeolite layer (Si/Al = ∞) was coated on an MFI-type zeolite membrane (Si/Al = 25). Using this two-layered membrane system, the olefin selectivity value increased to 85%; this was 19% higher than the value obtained during the single-layer membrane system. [ABSTRACT FROM AUTHOR]

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste. [ABSTRACT FROM AUTHOR]