TON-type Zeolites Research Articles

Unveiling the elusive role of tetraethyl orthosilicate hydrolysis in ionic-liquid-templated zeolite synthesis

Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1-butyl-3-methylimidazolium ([BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization.

In Situ Encapsulation of Pt Nanoparticles within Pure Silica TON Zeolites for Space-Confined Selective Hydrogenation.

Straightforward encapsulation of Pt clusters (∼2 nm) into the pure silica TON-type zeolite (ZSM-22) was reached in a dry gel conversion route, where the ionic liquid template was removed via the hydrocracking-calcination-reduction approach. The obtained Pt@ZSM-22 series possessed high crystallinity, large surface area, and ultrafine Pt clusters inside the zeolite crystals. They exhibited remarkable activity in the semi-hydrogenation of phenylacetylene into styrene; the lead sample with 0.2 wt % Pt loading afforded a large turnover number up to 117,787. The preferential high affinity of the pure silica ZSM-22-encapsulated Pt clusters toward the substrate phenylacetylene rather than the hydrogenated product was derived from the unique space-confinement effect of zeolite microchannels, which is responsible for such excellent performance.

Synthesis of ZSM-22 and Testing Its Catalytic Properties in the Ethylene Oxide Isomerization Reaction

The influence of the key parameters of the synthesis of a TON-type zeolite (ZSM-22) with or without an organic structure-directing agent on its phase composition has been established. The optimal composition of the reaction mixture and the crystallization time of ZSM-22 in the presence of 1,6-diaminohexane under static conditions have been determined. The dynamics of the formation of an impurity ZSM-5 by cocrystallization during the synthesis with stirring has been revealed. For zeolite ZSM-22 synthesized using the template-free procedure, the most important factors affecting the crystallinity and the crystallization time are the synthesis temperature, the amount of seed, and agitation of the reaction mixture. The zeolites synthesized according to the both procedures have been examined in the reaction of isomerization of ethylene oxide to acetaldehyde. Zeolite ZSM-22 obtained without adding the template is not inferior in activity to the zeolite of the same structure prepared in the presence of 1,6-diaminohexane. Moreover, it exhibits higher selectivity of ethylene oxide conversion to acetaldehyde. The complete conversion of ethylene oxide has been observed on ZSM-22 zeolites of both types at a reaction temperature of 400°C, the selectivity of its conversion to acetaldehyde being at least 93%.

Synthesis of Short, Needle-Shaped Crystals of TON-Type Zeolite by Addition of Inhibitors of Crystal Growth along the [001] Direction

TON-type zeolite crystals in the shape of short needles were synthesized using inhibitors of crystal growth along the [001] direction. When fluoride was used as a mineralizer, bulky amines incorporating structure-directing agents acted as inhibitors, while nonionic surfactants were more effective as inhibitors for decreasing the crystal length of TON-type zeolite. The amount of surfactant adsorbed on the zeolite increased with the surface area of the face containing pore mouths. This indicates that the surfactant was trapped in the pore mouths to inhibit crystal growth along the long axis of the needle-shaped crystals. By microscopic observation of the crystals, we confirmed inhibition of crystal growth by adsorption of the surfactant. After adsorption of Nile red, a lipophilic stain that is intensely fluorescent in surfactants, on as-synthesized zeolite, only the edges of the needle-shaped crystals were luminous, also indicating adsorption of the surfactant in pore mouths. When hydroxide was used as a mi...

Supporting Nickel To Replace Platinum on Zeolite Nanosponges for Catalytic Hydroisomerization of n-Dodecane

Hydroisomerization of linear paraffins to branched isomers is an important petrochemical process, which commonly uses a microporous zeolite catalyst supported with Pt metal nanoparticles. Although attempts were made in the past to find an alternative to costly Pt, replacement with low-cost metals was not successful for conventional bulk zeolites, due to the low metal dispersion resulting in poor catalytic performance. Here, we demonstrate that Ni can replace Pt when it is supported on zeolites with uniform mesopores. Ni-supported MFI-, *MRE-, and TON-type zeolites possessing mesopores showed the same or even better catalytic performance in comparison to that of Pt-supported conventional MFI, *MRE, and TON zeolites, respectively. The Ni-supported zeolites exhibited even better branched isomer yields, despite low Ni loading. This result is ascribed to the confinement or sandwiching effect of Ni nanoparticles by the mesopore walls in the zeolites, which stabilizes the highly dispersed Ni nanoparticles.

Nanocrystalline TON-type zeolites synthesized under static conditions

Pure-phase zeolites of the TON-type were synthesized under static hydrothermal conditions, which previously have, typically, required stirring during synthesis. Heterocyclic structure directing agents (SDAs) were observed to play important roles in both the selection of the polymorphs as well as in affecting the morphology of the particles formed. When an imidazole-based SDA was used snowflake-shaped particles formed, which indicated a dendritic growth pattern of the zeolite. These zeolite particles possessed intercrystalline mesopores. To the best of our knowledge, it is for the first time that snowflake-shaped particles have been observed for TON-type zeolites. Other synthesis parameters were optimized to obtain crystals with short c-axes. The c-axis shortened with an increased solid concentration used during synthesis. This shortening was attributed to both the degree of supersaturation, and a change of the crystal growth mechanism. Short c-axes could increase the concentration of pore mouths in TON-type zeolites. Altogether, synthesis of nanocrystalline zeolites of the TON type under static condition could, potentially, be advantageous to large-scale production.

Ionic Liquid assisted Synthesis of Zeolite-TON.

An ionic liquid assisted strategy for the synthesis of zeolitic material is reported. This strategy is a solid state synthetic method and the ionic liquid is employed as structure directing agent. A TON-type zeolite, which contains one-dimensional 10-member-ring, is successfully synthesized with the assistance of the ionic liquid, 1-ethyl-3-methylimidazolium bromide. This finding improves our understanding about the challenge of ionothermally synthesizing siliceous and aluminosilicate zeolites.

피페리딘형 구조유도분자를 이용한 알루미노실리케이트 제올라이트의 합성 및 특성 연구

Zeolites with different structures were synthesized from the hydrothermal synthesis condition employing simple structure directing agent (SDA) containing piperidine moiety. The gel containing :0.9SDA::0.217NaOH: was subject to hydrothermal synthesis at 413~453 K for 7 days. FER type zeolite was obtained at 433 K when piperidine was employed as SDA, whereas TON and MFI type zeolites were also obtained at 433 K when 2,6-dimethylpiperidine and 2,2,6,6-tetramethylpiperidine were used, respectively. Further increase of hydrothermal synthesis temperature to 453 K resulted in the formation of TON type zeolite when 2-mtheylpiperidine was used. The structural analysis of powder X ray diffraction pattern over FER type zeolite suggested that the SDA, piperidine interacted intimately with the zeolite where it located close to the framework.

Skeletal isomerization of tetradecane catalyzed by TON-type zeolites with a fragmented core–shell structure

TON-type zeolites with a core–shell structure were synthesized by crystal overgrowth of an aluminum-free TON-type zeolite on an aluminum-containing TON-type zeolite in the presence of fluoride ion, which was used as a mineralizing reagent to restrain the formation of defects. The core–shell structured zeolite showed greater selectivity for skeletal isomerization in tetradecane hydroisomerization because the acid sites on the external surface of needle-shaped crystals were passivated to inhibit cracking. Breaking the needle-shaped crystals of the core–shell structure to create shorter crystal pieces effectively enhanced the catalytic activity and selectivity for isomerization because new pore entrances were formed.

Conversion of Ethanol into Propylene over TON Type Zeolite

Conversion of Ethanol into Propylene over TON Type Zeolite

High pressure water intrusion investigation of pure silica 1D channel AFI, MTW and TON-type zeolites

Experimental water intrusion–extrusion isotherms were performed at room temperature on various 1D channel pure silica AFI, MTW and TON-type zeolites. The water intrusion is obtained by applying a high hydraulic pressure corresponding to the intrusion step. Whatever, the zeosil, when the pressure is released, the water extrusion occurs at a similar pressure to that of the intrusion one. These “zeosil–water” systems behave like a spring and the phenomenon is reproducible over several cycles. Several characterizations have been realized before and after water intrusion–extrusion experiments in order to reveal the presence or the absence of defects after such experiments. For all samples, no structural modifications at the long range order are observed by XRD analysis. However for the MTW-type zeosil, solid state NMR spectroscopy get evidence of the presence of Q 2 and Q 3 groups revealing the breaking of some siloxane bridges. Nevertheless, the amount of defects is very low (<2%) and seems not to have an influence on the intrusion–extrusion data for numerous cycles. The stored energy is relatively important and close to 5.8, 15 and 14 J/g for AFI, MTW and TON-type zeosils, respectively.

Preparation and characterization of SSZ-54: A family of MTT/ TON intergrowth materials

In this paper we report two different methods to prepare zeolites with framework structures that are intergrowths of the MTT and TON topologies. In one route we use a single structure-directing agent ( N-isopropylethylenediamine) in hydroxide mediated syntheses. The second method uses a mixture of structure-directing agent (SDA) molecules to prepare the MTT/ TON intergrowths. In this case, one molecule alone is selective for MTT-type zeolites and the other molecule alone is selective for TON-type zeolites. By varying the ratio of the individual molecules in the syntheses, we are able to systematically control the MTT or TON character of the intergrowth product. We find that one of the SDA molecules often has a stronger structure-directing or templating effect than the other molecule in the pair. For example, for the system involving mixtures of N-isopropyl-1,3-propanediamine and 1-methylbutylamine, the ratio of N-isopropyl-1,3-propanediamine:1-methylbutylamine in the gel must be below 0.25 before intergrowths are observed; otherwise, an MTT product is observed. We refer to this ability of one SDA molecule to dominate the phase selectivity (in a mixture) as a “dominant templating effect.” We have characterized the structural nature of the MTT/ TON intergrowths by a combination of techniques: comparison of experimental powder diffraction patterns with DIFFaX simulations, observations of systematic peak broadening in the experimental diffraction patterns, comparison of experimental diffraction patterns with those of small-crystallite samples of SSZ-32 ( MTT), and direct observation of stacking faults by high resolution transmission electron microscopy.

The bulk material dissolution method with small amines for the synthesis of large crystals of the siliceous zeolites ZSM-22 and ZSM-48

The hydrothermal reaction between silica glass and aqueous solutions of amines and sodium hydroxide has been investigated for the preparation of large crystals of siliceous zeolites. In the presence of n-butylamine at 160 °C needle-shaped crystals of ZSM-22 (TON-type) are formed. By adjusting the amount of n-butylamine used in crystallisation, crystals of up to 400 μm in length may be formed after 5 weeks of reaction. Calcination in air at 800 °C produces crystals free of template and scanning electron microscopy shows the samples to be free of cracks, with no evidence of loss of integrity of the specimens. The quality and indentity of the ZSM-22 crystals, both before and after calcination, is verified by using single crystal X-ray diffraction and 29Si MAS NMR and the refined structures compared to those previously reported for the same material. If the amine used in synthesis is 1,6-diaminohexane, usually used to prepare TON-type zeolites, then samples of ZSM-48, a disordered zeolite, are produced. These have very different crystal morphology, the samples being made up of intergrown plate-shaped crystallites agglomerated into spherical objects. The results we present illustrate the scope for the general use of the ‘bulk material dissolution’ method in the synthesis of siliceous zeolites as large single crystals.

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

A critical review of the adsorption and catalysis of n- and methylalkanes demonstrates that the interior surface of TON- and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n- and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n- and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface “pore mouth” or “key-lock” adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA- and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis.

Hydrothermal Synthesis of Calcium and Boron Containing MFI-Type Zeolites by Using Organic Amine as Structure Directing Agent

The hydrothermal syntheses of MFI-type zeolites, MFI and calcium-containing MFI (Ca-MFI), were systematically studied by using simple and inexpensive organic amines, triethylamine (TEA), butylamine (NBA), and 1,6-diaminohexane (DAH), as structure-directing agent (SDA). Boron-containing Ca-MFI ([B]-Ca-MFI) zeolites were also examined by using TEA as SDA. The pure phase of MFI was obtained under appropriate conditions and found that TEA plays an important role as SDA. Resulting Ca-MFI zeolites had hexagonal morphologies, and [B]-Ca-MFI zeolites, of which the morphology was a sticklike prism, had the smaller particle size than Ca-MFI zeolites. The strong acid sites were found over both Ca- and [B]-Ca-MFI zeolites after ion exchange to proton-type form. The incorporated calcium into MFI zeolites by using triethylamine was not leached significantly during the ion exchange compared to the conventional MFI zeolites synthesized by using tetrapropylammonium bromide as SDA. Topological changes from MFI zeolites to TON-type zeolites with NBA and DAH as SDA were observed by changing from static to rotating conditions.

Bifunctional catalytic isomerization of decane over MTT-type aluminosilicate zeolite crystals with siliceous rim

Micrometer-size MTT-type zeolite crystals with aluminum depletion in the outer layer were synthesized. The compositional variation in individual crystals was obtained by altering the chemical composition of the gel during crystal growth of MTT-type zeolite. Chemical composition of the bulk and the surface of the crystals was determined using 27Al MAS NMR and XPS, respectively. The zeolite with siliceous rim was converted into a bifunctional catalyst by neutralizing the cation-exchange capacity with protons and plating with a trace amount of platinum metal. The MTT zeolite with siliceous crystal termination was catalytically much less active than the isostructural ZSM-23 zeolite with homogeneous chemical composition. The catalytic activity reflects the aluminum content on the surface of the crystals determined by XPS, rather than the bulk composition. The reaction mechanism and the reaction kinetics were analyzed using a microkinetic model developed previously for the structurally related TON-type zeolite. The catalytic data are in favor of the pore mouth catalysis model of skeletal isomerization of long n-alkanes on 10-membered ring tubular pore zeolites.

Thermal stability and siting of aluminum in isostructural ZSM-22 and Theta-1 zeolites

Conventional 29Si and 27Al MAS NMR techniques and 27Al two-dimensional Multiple Quantum Magic Angle Spinning (2D MQMAS) NMR technique were used to characterize two isostructural TON type zeolites (Theta-1, ZSM-22). Nonuniform distribution of framework aluminum and the preferential population of T3 and T4 sites by the aluminum atoms in the TON material were established. The aluminum sites of Theta-1 sample showed higher thermal stability compared to ZSM-22 sample, despite of the higher aluminum content and higher calcination temperature. It was shown that 27Al 2D MQMAS NMR technique can be used for monitoring the minute differences in the surrounding of aluminum T sites, caused by the different templates and the post-synthesis treatments.

Preparation of Boron-containing TON-Type Zeolite by Self-transformation of Porous Glass in a Vapor Phase

Abstract Pure phase of boron-containing TON-type zeolite with high crystallinity was prepared by self-transformation of porous glass granules in a vapor phase of methylamine and water. XRD and 11B, 27Al and 29Si MAS NMR spectra proved that the atoms of B, Al and Si in the raw glass have been essentially completely incorporated into the zeolite framework.

Template removal from molecular sieves by low-temperature plasma calcination

The oxidative removal of templates from crystals of MFI- and TON-type zeolites using low-temperature oxygen plasma at 370 K has been investigated. This treatment removes tetrapropylammonium inside 5 µm lengths of channels in the completely siliceous MFI structure (silicalite), and diethylamine to a depth of at least 70 µm in the channels of the completely siliceous TON structure. Substitution of B, Al or Fe into the framework of silicalite significantly obstructs the removal of tetrapropylammonium, but complete decomposition of the template can be accomplished in small samples of [Si, B]-MFI. A comparison of plasma calcination with thermal calcination in air indicates that the release of boron into extra-framework positions upon either treatment is caused by the slow desorption of water at the calcination temperature.