High-silica Mordenite Research Articles

Steering polymer growth by molding nanochannels: 1,5-hexadiene polymerization in high silica mordenite

Zeolites are known as scaffolds for the assembly of molecules via non-covalent interactions yielding organized supramolecular materials. Yet their potential in driving the growth of low-dimensional systems requiring covalent bond formation is still unexplored. We incorporated 1,5-hexadiene in the channels of a high-silica mordenite and analyzed the material by infrared spectroscopy, X-ray powder diffraction, thermogravimetry and modeling techniques. Due to the few zeolite acid sites, 1,5-hexadiene experiences a slow conversion to a polymer mainly formed by cyclopentane units and featuring short side chains that are able to fit the channels. The shape-directing abilities of zeolite frameworks play a two-fold role, involving first the organization of the monomers inside the void-space and then the linear growth of the chain dictated by the channel geometry. These findings highlight the molding action of zeolites in directing transformations of covalent bonds under ambient conditions and may provide insights for obtaining confined polymers with intriguing prospective applications.

Simultaneous removal of ammonium ions and sulfamethoxazole by ozone regenerated high silica zeolites

Continuous development of industry and civilization has led to changes in composition, texture and toxicity of waste water due to the wide range of pollutants being present. Considering that the conventional wastewater treatment methods are insufficient for removing micropollutants and nutrients to a high level, other, alternative, treatment methods should be used to polish wastewater treatment plant effluents. In this study we developed an alternative, polishing concept for removal of ammonium and micropollutants that could potentially be incorporated in existing wastewater treatment plants. We demonstrated a method to use high silica MOR zeolite granules as an adsorbent for simultaneous removal of the micropollutant sulfamethoxazole (SMX) and ammonium (NH4+) ions from aqueous solutions. At an initial NH4+ concentration of 10 mg/L the high silica zeolite mordenite (MOR) granules removed 0.42 mg/g of NH4+, similar to the removal obtained by commonly used natural zeolite Zeolita (0.44 mg/g). However, at higher NH4+ concentrations the Zeolita performed better. In addition, the Langmuir isotherm model showed a higher maximum adsorption capacity of Zeolita (qmax, 4.08 mg/g), which was about two times higher than that of MOR (2.11). The adsorption capacity of MOR towards SMX, at both low (2 µg/L) and high (50 mg/L) initial concentrations, was high and even increased in the presence of NH4+ ions. The used adsorbent could be regenerated with ozone and reused in consecutive adsorption–regeneration cycles with marginal decrease in the total adsorption capacity.

High-silica mordenite as scaffold for phenylacetylene polymerization: In situ high pressure investigation

Abstract The joint use of high pressure and regular void-space architectures is a promising route to obtain new nanomaterials with unique properties. We explore herein the pressure-driven injection of aromatic guest species inside zeolite mordenite. Monomeric phenylacetylene (PhA), used as pressure transmitting medium, was inserted in high-silica mordenite at high pressure conditions. In-situ X-ray powder diffraction and IR spectroscopy analyses show that the combined action of high pressure, temperature and zeolite pores accomplish the intrusion of phenylacetylene and its conversion to oligomeric species exhibiting a greater degree of conjugation with respect to the starting monomer. This study may open a new path for the realization of composite materials with interesting optoelectronic properties via pressure-driven intrusion and polymerization of aromatic molecules inside zeolite frameworks.

Thermal behavior of high silica mordenite

Abstract This work studies the thermal stability, heat-induced structural deformations, and dehydration/rehydration dynamics of a synthetic high silica mordenite. It is of special interest because this particular phase has proven to be an ideal host for the encapsulation of several kinds of organic molecules making it a promising scaffold for drug delivery. The dehydration process was followed by thermal analysis, infrared spectroscopy in controlled atmosphere, in situ synchrotron XRPD, and structural refinement. Overall, all the results indicate weak interactions of H2O molecules with the silicatic mordenite framework and evidence the presence of hydroxyl groups with different condensation responses at high temperature. Infrared characterization highlighted how the desorption of adsorbed H2O molecules under degassing is already complete at rT. The unit cell parameters exhibit very slow and almost isotropic changes upon heating. Above 550 °C an increase in slope is observed for all parameters. This corresponds to the marked silanol condensation and consequent framework reassessment observed at this temperature by infrared characterization. Overall cell contractions are 0.67%, 1.18%, and 0.81% for a, b, c, respectively and 2.64% for cell volume. HS-MOR undergoes very moderate T induced deformations, indicating a very rigid and stable framework.

Trivalent ions modification for high-silica mordenite: A first principles study

Abstract Using periodic DFT-D3-U methods, the present work give a mechanistic insight into the high silica B-, Al-, Ga- and Fe-MOR with H, Li, Na, and K as charge balance ions. The acid properties of the zeolite were probed via NH3 and pyridine adsorption. It is found that the charge balance ions influence the location of the trivalent ions, the cell volumes, as well as the synthesis difficulty of the zeolites. The energy differences for B, Al, Ga and Fe in different T sites are small for the H-form zeolites, while large for the Na- and K-form zeolites. For H-form MOR, the proton of the OH group prefers to bond to O(7) and O(3) and pointing to the 12MR for trivalent ions in T1 sites. The proton bonds to O(3), O(2), O(2) and O(5), respectively, for B, Al, Ga and Fe in T2 site of MOR, with the OH group pointing to intersection of 12MR and the side-pocket, except for the B-MOR that OH group pointing to the 12MR. For trivalent ions located in T3 and T4 sites, the protons prefers to bond to O(1) and O(2), respectively, with the OH group pointing to the intersection of 8MR and side-pocket as well as the intersection of 12MR and side-pocket. All incorporated B, Al, Ga, and Fe framework ions are tetra-coordinated, except the B atoms are tri-coordinated. The NH4-form MOR has smaller cell volume than the other form MOR. Na and K are energetically more favored charge balance ions than Li and NH3 for MOR zeolites synthesis, and the H-form zeolite is the most difficult to be synthesized directly. The strength of the Bronsted acidity follows the order: HBMOR

Direct Synthesis of 2,5-Diformylfuran from Carbohydrates Using High-Silica MOR Zeolite-Supported Isolated Vanadium Species

Directly transforming carbohydrates into high value-added chemicals provides an economic and sustainable path for the utilization of the renewable biomass resource. Herein, we fabricated an efficient catalytic system for the straightforward conversion of various carbohydrates into 2,5-diformylfuran (DFF) by using vanadium oxide supported on high-silica mordenite (MOR) zeolites in the presence of hydrochloric acid. The synthesis of high-silica MOR zeolites was achieved in a template-free dense system featuring energy savings and environmental friendliness, delivering the SiO2/Al2O3 ratio up to 80. The conversion of fructose into DFF reached a high yield of 96.0% in a one-pot and one-step reaction by oxidation with atmospheric O2 (balloon), with facile recovery and good reusability of the catalyst. Good yields were also obtained in the direct synthesis of DFF from other carbohydrates including glucose, sucrose, inulin, raffinose, maltose, and starch. The high performance relied on the unique high-silica MOR...

Mordenite zeolite with ultrahigh SiO2/Al2O3 ratio directly synthesized from ionic liquid-assisted dry-gel-conversion

SiO2/Al2O3 ratio (SAR) is one of the most important parameters for zeolite materials, and tuning of SAR towards required topology is crucial for applications of zeolites. Mordenite (MOR) zeolites normally possess the moderate SARs of about 4–32. In this work, a breakthrough for straightforward synthesis of high-silica MOR zeolites was achieved without using seed or fluoride additive, attaining well crystallized MOR with wide window of SARs in the range of 11–263, in which the ultrahigh SAR of 263 represented the highest value for MOR up to date. The synthesis relied on the gel preparation by acidic hydrolysis of the silica precursor with the ionic liquid (IL), 1-butyl-3-methylimidazolium bromide ([BMIm]Br), as the structure-direct-agent, followed by dry-gel-conversion (DGC). Besides mordenite, ZSM-5 could be also obtained from this route. Thermal stability tests demonstrated that the obtained ultrahigh-silica MOR zeolites preserved the crystalline structure up to 800 °C, and the higher SAR, the better thermal stability. Our synthesis largely expands the SAR range of MOR zeolites and provides a series of highly thermal stable high-silica MOR zeolites as promising catalyst supports.

Pressure-induced penetration of guest molecules in high-silica zeolites: the case of mordenite.

A synthetic high-silica mordenite (HS-MOR) has been compressed in both non-penetrating (silicone oil, s.o.) and penetrating [methanol : ethanol : water (16 : 3 : 1) (m.e.w.), water : ethanol (3 : 1) (w.e.), and ethylene glycol (e.gl.)] pressure transmitting media (PTM). In situ high-pressure (HP) synchrotron X-ray powder diffraction (XRPD) experiments allowed the unit cell parameters to be followed up to 1.6, 1.8, 8.4, and 6.7 GPa in s.o., w.e., m.e.w., and e.gl., respectively. Moreover, e.gl. was also used as a PTM in in situ HP Raman and ex situ IR experiments. The structural refinement of HS-MOR compressed in e.gl. at 0.1 GPa - the lowest investigated pressure - revealed the presence of 3.5 ethylene glycol molecules per unit cell. The infrared spectrum of the recovered sample, after compression to 1 GPa, is consistent with the insertion of ethylene glycol molecules in the pores. XRPD and Raman spectroscopy experiments performed under pressure indicated the insertion of a small number of guest molecules. Ethylene glycol is partially retained inside mordenite upon pressure release. A symmetry lowering was observed in s.o. above 0.8 GPa, while above 1.6 GPa the patterns indicated a rapid loss of long range order. From ambient pressure (Pamb) to 1.6 GPa, a high cell volume contraction (ΔV = -9.5%) was determined. The patterns collected with penetrating PTM suggested the penetration of guest molecules into the porous host matrix, starting from a very low P regime. The entrapment of PTM molecules inside micropores contributes to the stiffening of the structure and, as a consequence, to the decrease of the compressibility with respect to that measured in s.o. From the structural point of view, HS-MOR reacts to compression and to the penetration of different guest species with appropriate framework deformations. Interestingly, ethylene glycol is partially retained inside mordenite upon pressure release, which is of importance for potential application of this composite material.

2D–3D structures: The hydrothermal transformation of a layered sodium silicate, Na-RUB-18, into mordenite zeolite

The synthesis of the high-silica mordenite zeolite by hydrothermal transformation of the Na-RUB-18 layered silicate was conducted by the addition of Al[OCH(CH3)2]3 or Na2Al2O4 into the gel after 7days of hydrothermal treatment of a non-aluminum gel. Extensive characterization showed that the samples were obtained in good crystallinity in periods varying from 7 to 14days after the addition of the aluminum source when Al[OCH(CH3)2]3 was used and after 14days for Na2Al2O4. Results of 29Si and 27Al NMR suggest a gradual transformation of Na-RUB-18 into MOR by the appearance of signals which correspond to silicon atoms coordinated to 1and 2 Al and one signal corresponding to tetrahedrally coordinated aluminum atoms, both nonexistent in Na-RUB-18.

The interactions of methyl tert-butyl ether on high silica zeolites: a combined experimental and computational study

In this work, the interactions of methyl tert-butyl ether (MTBE) on different dealuminated high silica zeolites were studied by means of both experimental and computational approaches. Zeolites with different textural and surface features were selected as adsorbents and the effect of their physico-chemical properties (i.e. pore size architecture and type and amount of surface OH sites) on sorption capacity were studied. High silica mordenite (MOR) and Y zeolites (both with a SiO2/Al2O3 ratio of 200) and ZSM-5 solid (SiO2/Al2O3 ratio of 500) were selected as model sorbents. By combining FTIR and SS-NMR (both (1)H and (13)C CPMAS NMR) spectroscopy it was possible to follow accurately the MTBE adsorption process on highly defective MOR characterized by a high concentration of surface SiOH groups. The adsorption process is found to occur in different steps and to involve isolated silanol sites, weakly interacting silanols, and the siloxane network of the zeolite, respectively. H-bonding and van der Waals interactions occurring between the mordenite surface and MTBE molecules were modeled by DFT calculations using a large cluster of the MOR structure where two adjacent side-pockets were fused in a large micropore to simulate a dealumination process leading to silanol groups. This is the locus where MTBE molecules are more strongly bound and stabilized. FTIR spectroscopy and gravimetric measurements allowed determination of the interaction strength and sorption capacities of all three zeolites. In the case of both Y and MOR zeolites, medium-weak H-bonding with isolated silanols (both on internal and external zeolite surfaces) and van der Waals interactions are responsible for MTBE adsorption, whereas ZSM-5, in which a negligible amount of surface silanol species is present, displays a much lower amount of adsorbed MTBE retained mainly through van der Waals interactions with zeolite siloxane network.

Adsorption and reaction of sulfachloropyridazine sulfonamide antibiotic on a high silica mordenite: A structural and spectroscopic combined study

Owing to their acidic nature, sulfonamide antibiotics concentrate in anionic form in water bodies where they can remain unchanged for long periods of time, accounting for great concern for antibiotic-resistance issues. In this study the removal of sulfachloropyridazine (4-amino-N-(6-Cl-3-pyridazinyl)benzene sulfonamide) antibiotic from water by adsorption on a high silica mordenite with channel window dimension comparable to that of the antibiotic, and with a significant concentration of internal silanol groups due to the dealumination process, was investigated. The adsorption of sulfachloropyridazine by mordenite at room temperature was completed within 4h with the maximal amount of adsorbed antibiotic of 15.1% zeolite dry weight. The desorption trials elucidated the irreversibility of the adsorption process. The embedding of sulfachloropyridazine into mordenite channels was confirmed by a combined XRPD and FTIR study. Rietveld structure refinement revealed that the incorporation of sulfachloropyridazine molecules caused changes in the dimension of the zeolite channel systems, when compared to the parent zeolite, and a close vicinity of the heterocycle ring nitrogen to the oxygens of mordenite side pocket. FTIR revealed a strong perturbation of the vibrational modes of both the pyridazinyl ring and mordenite silanol groups upon antibiotic adsorption. When the adsorption was conducted at 65°C, an unfavourable temperature effect was highlighted and, interestingly, sulfachloropyridazine transformed with 100% selectivity to 4-amino-N-(6-hydroxyl-3-pyridazinyl)benzene sulfonamide. A nucleophilic aromatic substitution (SNAr) mechanism was suggested for the formation of the reaction product. It is proposed that the H-bond between mordenite silanol groups and pyridazine nitrogen atom, clearly detected by FTIR, stabilize in the ring partial positive charges favouring the displacement of the chloride leaving group.

Tritium Removal from Tritiated Water Using Mesoporous Silica

The ability of various solid adsorbents to adsorb tritium from tritiated water was studied. The tritium removability and adsorption ability of mesoporous silica (MCM-41) were found to be larger than those of conventional microporous zeolites such as mordenite (MOR) and Linde-type A (LTA). The different adsorbents can be arranged in order of tritium removability and tritium adsorption ability as follows: MCM-41 > LTA(5A) > high-silica MOR ≈ low-silica MOR ≈ LTA(4A). The adsorbents can also be arranged in decreasing order of the separation factor (α) as follows: MCM-41 > LTA(5A) > low-silica MOR ≈ LTA(4A) > high-silica MOR.

Hydrothermal synthesis of high-silica mordenite by dual-templating method

High-silica mordenite (MOR) zeolites were hydrothermally synthesized by a dual-templating method using tetraethylammonium hydroxide (TEAOH) and hexamethyleneimine (HMI) as co-structure-directing agents (SDAs). The MOR zeolites were crystallized readily with the addition of NH 4NO 3 from the gels that had a Si/Al ratio up to 60. The synthesis resulted in highly crystalline MOR zeolites possessing a Si/Al ratio of 37.1. The chemical coordination states of the Al ions in the MOR zeolites were characterized by 27Al and 29Si NMR MAS spectroscopy. The Al ions occupied dominantly the tetrahedral sites in the framework. The dual-templating effect that the two amines exhibited on the zeolite crystallization was investigated by 13C MAS NMR spectroscopy and elemental analyses. Both organic SDA molecules were incorporated simultaneously into the zeolite products, corresponding to 65% of TEA + and 35% of HMI. These two kinds of SDAs played a cooperative role in the nucleation and crystallization of the MOR structure under high silica conditions.

Multinuclear gallium-oxide cations in high-silica zeolites

Periodic DFT calculations of the stability of mononuclear and oligonuclear Ga-oxo cations in mordenite (MOR) have been carried out. Independent of the aluminium distribution in the zeolite framework the stability of cyclic Ga(2)O(2)(2+) ions is much higher than that of the isolated GaO(+) (gallyl) ions in a high-silica mordenite (Si/Al = 23) model. As to the location of such dimers, favorable tetrahedral coordination environment of Ga dominates over the necessity to compensate the positive extraframework charges directly with proximate negative framework charges. Charge alternation can occur in Ga(2)O(2)/MOR models in which positive charges of the cationic complex are separated from the framework anionic sites. Oligomerization of four isolated gallyl ions in a MOR model with Si/Al = 11 results in the formation of cubic Ga(4)O(4)(4+) ions. Also in this case direct interaction of the cluster is limited to two anionic sites, while two other framework [AlO(2)](-) units are significantly remote. Binuclear sites are argued to account for the enhanced activity of oxygenated gallium-exchanged high-silica zeolites in alkane dehydrogenation. These sites, however, tend to decompose via water desorption upon the catalytic reaction resulting in less reactive reduced Ga(+) ions. As per predictions from the quantum-chemical calculations, the experimental results show that the high alkane dehydrogenation activity can be maintained by in situ hydrolysis of the reduced extraframework Ga species.

Enhancement of the photocatalytic reactivity of TiO2 nano-particles by a simple mechanical blending with hydrophobic mordenite (MOR) zeolite

The photocatalytic oxidation of gaseous acetaldehyde with O2 on commercial TiO2 nano-particles could be successfully enhanced by a simple mechanical blending with a high-silica mordenite (MOR) zeolite, the surface of which showed high hydrophobic properties. When the TiO2 nano-particles of ca. 5–20wt% were mixed with the MOR zeolite powders in an agate mortar for only 5min, the blended TiO2/MOR samples showed higher photocatalytic reactivity as compared to the pure TiO2 nano-particles. Since the high-silica zeolite powders are highly transparent in UV light regions, the incident UV light is effectively irradiated onto the whole part of the TiO2 nano-particles without any loss of light intensity. Furthermore, the siliceous MOR zeolite powders effectively adsorb the gaseous acetaldehyde molecules and supply them onto the surfaces of the blended TiO2 nano-particles, resulting in an enhancement of the photocatalytic reactivity.

Structural and physico-chemical properties of high-silica mordenite

The structural and physico-chemical properties of high-silica mordenite (MOR) zeolite were investigated using chemical computational techniques and then the results obtained were compared with our experimental data. With an increase in the size of structure model in which each four non-equivalent crystallographic tetrahedral site (T site) was substituted by Al atom, the order of stabilization energy varied. However, T3 site present in side pocket was energetically the most stable one among these four sites regardless of the model employed, namely it was found that Al atom is preferentially sitting in the T3 site of MOR zeolite.

Aluminum distribution in high-silica mordenite

The Al distribution in high-silica mordenite (MOR) zeolites with various Si/Al ratios was investigated by FT-IR spectroscopy in the presence of CD3CN probe molecules and benzene adsorption. Two adsorption bands assigned to CN stretching vibration were observed at 2280–2295 and ≈2315 cm−1, which are due to interaction of CN with acidic hydroxyl groups in the main channels and the side pockets of H-MOR zeolite, respectively. The relative intensity of the peak at 2315 cm−1 increased with an increase in the Si/Al ratio, indicating that the proportion of Al atoms in the main channels relatively decreased with the Si/Al ratio. This was confirmed from the linear relationship between the number of benzene molecules adsorbed in a unit cell and the number of Al atoms in the main channels. In addition, this was also suggested from the computer simulation result that Al atoms are preferentially sitting in the T3 site.

Control of crystal size of high-silica mordenite by quenching in the course of crystallization process

An influence of quenching in the course of crystallization process of high-silica mordenite zeolite (MOR) on the crystallization rate and crystal size was investigated in detail. It was found that the crystallization rate is considerably enhanced by the quenching, and that the crystal size decreases with the quenching time. The high-silica MOR with a crystal size of 500–700 nm was easily obtained by a combination of the quenching and the addition of seed crystals. There are no differences in the thermal stability and dealumination behavior between MORs synthesized with and without quenching during crystallization.

Characterization of High Silica Mordenite Synthesized from Amine-free System Using Fluoride as Structure-directing Agent

Characterization of High Silica Mordenite Synthesized from Amine-free System Using Fluoride as Structure-directing Agent

Effect of ammonium salts on hydrothermal synthesis of high-silica mordenite

Effect of ammonium salts on the direct hydrothermal synthesis of high-silica mordenite (MOR) zeolite with tetraethylammonium hydroxide was investigated. The addition of NH 4NO 3 to the system restrained the formation of MFI zeolite and quartz, and accelerated the crystallization rate of high-silica MOR zeolite. The MOR zeolite synthesized with NH 4NO 3 was very poorer in framework defects as compared with sample obtained without NH 4NO 3 as indicated by IR and 29Si MAS NMR techniques. It was also indicated by nitrogen adsorption study that the micropore and external surface areas of the MOR zeolites synthesized with ammonium salts are considerably larger than that of sample without ammonium salts. Under well-optimized conditions, the highly crystalline and pure MOR zeolite with a Si/Al ratio of ≈34 was successfully prepared by adding seed crystals and NaF as well as NH 4NO 3.