Mordenite Zeolite Research Articles

Channeling carbon dioxide

Gas Separation The separation of gas molecules with physisorbents can be challenging because there is often a tradeoff between capacity and selectivity. Zhou et al. report a template-free hydrothermal synthesis of the one-dimensional channel zeolite mordenite, in which some silicon was replaced by iron. Rather than forming a powder that requires further shaping, this mechanically stable material self-assembled into monoliths. Iron atoms bound in tetrahedral zeolite sites narrowed the channels and enabled the size-exclusion separation of carbon dioxide (CO2) over nitrogen (N2) and methane. High CO2 uptake and highly efficient CO2–N2 separation was demonstrated for both dry and humid conditions. Science , aax5776, this issue p. [315][1] [1]: /lookup/doi/10.1126/science.aax5776

Low temperature ethanol dehydration performed by MOR catalysts obtained from 2D–3D transformation

The silanol groups present on the surface of lamellar silicates are excellent reaction sites for a varied number of chemical modifications. The conversion of these solids into zeolitic structures has shown to be an interesting synthetic alternative, once avoiding hard templating methods and producing materials with particular characteristics. In this work, a post-synthesis OSDA-free procedure was employed for the 2D–3D transformation of Na-RUB-18 lamellar silicate into mordenite zeolite. The conversion was performed at 140 °C and produced small zeolitic crystals (300–500 nm) after 12 and 24 h of crystallization. The reaction presented 65% yield (mol/mol SiO2), producing materials with a similar Si/Al molar ratio (around 6). The 27Al MAS NMR spectra showed signals related to tetrahedrally coordinated aluminum. The N2 adsorption/desorption isotherms confirmed the solids microporous nature and volume (0.36 and 0.43 cm3 g−1). The number of acidic sites was determined by NH3-TPD (976 and 848 µmol g−1), which also revealed sites with weak and moderate to strong acidity. Finally, the samples’ catalytic activity was evaluated by the ethanol dehydration reaction performed at low temperature (150 °C). The synthesized materials were compared to a commercial sample and all the catalysts showed ethanol conversion around 70%, producing ethene and diethyl ether; the latter being the major product at the employed temperature. Unlike the commercial sample, the synthesized ones did not present any deactivation during the time on stream. This feature was attributed to their low-defect structure and subtle mesoporosity.

Critical Role of Al Pair Sites in Methane Oxidation to Methanol on Cu-Exchanged Mordenite Zeolites

Cu-exchanged aluminosilicate zeolites have been intensively studied for the selective oxidation of methane to methanol via a chemical looping manner, while the nature of active Cu-oxo species for these catalysts is still under debate. This study inquired into the effects of Al distribution on methane oxidation over Cu-exchanged aluminosilicate zeolites, which provided an effective way to discern the activity difference between mononuclear and polynuclear Cu-oxo species. Specifically, conventional Na+/Co2+ ion-exchange methods were applied to quantify isolated Al and Al pair (i.e., Al−OH−(Si−O)1–3−Al−OH) sites for three mordenite (MOR) zeolites, and a correlation was established between the reactivity of the resultant Cu-MOR catalysts and the portions of the accessible framework Al sites. These results indicated that the Cu-oxo clusters derived from the Al pair sites were more reactive than the CuOH species grafted at the isolated Al sites, which is consistent with in situ ultraviolet-visible spectroscopic characterization and density functional theory calculations. Further theoretical analysis of the first C–H bond cleavage in methane on these Cu-oxo species unveiled that stabilization of the formed methyl group was the predominant factor in determining the reactivity of methane oxidation.

Nano architectured cues as sustainable membranes for ultrafiltration in blood hemodialysis

Membranes with zeolites are encouraging for performing blood dialysis because zeolites can eliminate uremic toxins through molecular sieving. Although the addition of various pore-gen and adsorbent in the membrane can certainly impact the membrane production along with creatinine adsorption, however, it is not directed which pore-gen along with zeolite leads to better performance. The research was aimed at reducing the adsorption of protein-bound and uremic toxins by using mordenite zeolite as an adsorbent while polyethylene glycol and cellulose acetate as a pore generating agent. Membranes were cast by a phase-inversion technique which is cheap and easy to handle as compared to the electro-spinning technique. Through this strategy, the ability to adsorb creatinine and solute rejection percentage were measured and compared against the pristine PSU, when only PEG was used as a pore-modifier and when PEG along with CA was used as a pore-modifier along with a different concentration of zeolite. The experiments revealed that PEG membranes can give a better solute rejection percentage (93%) but with a low creatinine adsorption capacity that is 7654 μg/g and low bio-compatibility (PRT 392 s, HR 0.46%). However, PEG/CA membranes give maximum creatinine adsorption that is 9643 μg/g and also better bio-compatibility (PRT 490 s, HR 0.37%) but with a low BSA rejection (72%) as compared to the pristine PSU and PEG membranes. The present study finds that the concentration of mordenite zeolite affects the membrane performance because its entrapment and large pore size of the membrane decreases solute rejection but increases creatinine uptake level along with the better bio-compatibility.

Removal of Transition Metals from Contaminated Aquifers by PRB Technology: Performance Comparison among Reactive Materials.

The most common reactive material used for the construction of a permeable reactive barrier (PRB) is zero valent iron (ZVI), however, its processing can generate corrosive effects that reduce the efficiency of the barrier. The present study makes a major contribution to understanding new reactive materials as natural and synthetic, easy to obtain, economical and environmentally friendly as possible substitutes for the traditional ZHV to be used as filters in the removal of three transition metals (Zn, Cu, Cd). To assess the ability to remove these pollutants, a series of batch and column tests were carried out at laboratory scale with these materials. Through BACH tests, four of seven substances with a removal percentage higher than 99% were prioritized (cabuya, natural clinoptilolite zeolites, sodium mordenite and mordenite). From this group of substances, column tests were performed where it is evidenced that cabuya fiber presents the lowest absorption time (≈189 h) while natural zeolite mordenite shows the highest time (≈833 h). The latter being the best option for the PRB design. The experimental values were also reproduced by the RETRASO code; through this program, the trend between the observed and simulated values with respect to the best reactive substance was corroborated.

Efficient Synthesis of Mordenite Zeolite for Dimethyl Ether Carbonylation

Efficient Synthesis of Mordenite Zeolite for Dimethyl Ether Carbonylation

Methane Over-Oxidation by Extra-Framework Copper-Oxo Active Sites of Copper-Exchanged Zeolites: Crucial Role of Traps for the Separated Methyl Group.

Copper-exchanged zeolites are useful for stepwise conversion of methane to methanol at moderate temperatures. This process also generates some over-oxidation products like CO and CO2 . However, mechanistic pathways for methane over-oxidation by copper-oxo active sites in these zeolites have not been previously described. Adequate understanding of methane over-oxidation is useful for developing systems with higher methanol yields and selectivities. Here, we use density functional theory (DFT) to examine methane over-oxidation by [Cu3 O3 ]2+ active sites in zeolite mordenite MOR. The methyl group formed after activation of a methane C-H bond can be stabilized at a μ-oxo atom of the active site. This μ-(O-CH3 ) intermediate can undergo sequential hydrogen atom abstractions till eventual formation of a copper-monocarbonyl species. Adsorbed formaldehyde, water and formates are also formed during this process. The overall mechanistic path is exothermic, and all intermediate steps are facile at 200 °C. Release of CO from the copper-monocarbonyl costs only 3.4 kcal/mol. Thus, for high methanol selectivities, the methyl group from the first hydrogen atom abstraction step must be stabilized away from copper-oxo active sites. Indeed, it must be quickly trapped at an unreactive site (short diffusion lengths) while avoiding copper-oxo species (large paths between active sites). This stabilization of the methyl group away from the active sites is central to the high methanol selectivities obtained with stepwise methane-to-methanol conversion.

Role of Brønsted Acid Sites within 8-MR of Mordenite in the Deactivation Roadmap for Dimethyl Ether Carbonylation

Mordenite zeolite is now the most promising catalyst for the carbonylation of dimethyl ether (DME) to methyl acetate because of the excellent initial activity and selectivity, but it suffers from r...

Ammonia adsorption by L-type zeolite and Prussian blue from aqueous and culture solutions

Modern regenerative medicine and pharmaceutical manufacturing require a large-scale culture of cells. Consequently, cells must be suspension-cultured at high densities, which is challenging because more metabolites, especially ammonia, are produced that inhibit cell proliferation. To address this problem, we tested four zeolites (L-type zeolite, ferrierite, mordenite, and Y-type zeolite) and Prussian blue for their ability to adsorb NH4+ (the predominant form of ammonia in a culture-solution pH) from an aqueous solution and a culture solution. The L-type zeolite and Prussian blue effectively adsorbed NH4+ from aqueous solutions, while the other absorbents were ineffective. Notably, neither adsorbent removed glucose, a representative nutrient, from the aqueous solution. Kinetics and equilibrium studies revealed that both adsorbents (L-type zeolite and Prussian blue) obey pseudo-second-order kinetics and are well fitted by the Langmuir isotherm model. The L-type zeolite also exhibited a high NH4+-adsorption in the culture solution. Further, while the L-type zeolite exhibited minimal cytotoxicity, Prussian blue was cytotoxic. Using the L-type zeolite for adsorption is simple and cost-effective, thus making it a suitable NH4+ adsorbent for culture solutions. Furthermore, reusing an expensive culture solution on a large scale can effectively lower costs of producing cell cultures intended for pharmaceutical manufacturing and regenerative medicine purposes. Thus, it is expected that this method will be used to regenerate culture solutions on a large-scale.

Crystal size sensitivity of HMOR zeolite in dimethyl ether carbonylation

The effect of crystal size of HMOR from micro size to 50 nm, with the apparent similar acid site density, on catalytic performance for the dimethyl ether (DME) carbonylation was investigated. The crystal size of HMOR is sensitive to the deactivation rate of DME carbonylation reaction, and the higher stability around 200 nm can be achieved. The characterization studies reveal that the diffusions of MA product play a key role during the induction and deactivation period in DME carbonylation. These will be helpful for guiding the large-scale synthesis of mordenite zeolites catalysts with high efficiencies for DME carbonylation.

Copper-Oxo Active Sites in the 8MR of Zeolite Mordenite: DFT Investigation of the Impact of Acid Sites on Methanol Yield and Selectivity

There is significant interest in improving methanol yields from methane in copper-exchanged zeolites. Interestingly, zeolites with proton, H+, precursors provide greater methanol yields and selecti...

DESALINATION BEHAVIOR OF NATURAL ZEOLITE IN SEAWATER

In recent years, it has been considered to secure water and food using seawater desalination technology, and a new simple desalination material for reducing high concentration sodium chloride in seawater is required. In this study, desalting agents were prepared from natural zeolite with addition of calcined Ca-Fe type layered double hydroxide (LDH) to desalinate seawater for agricultural use. Mordenite type natural zeolite from Fukushima, Japan was used. The salinity and pH of seawater used in this study were 3.61% and 8.0, respectively. When more than 250 g/L of natural zeolite was added, the salinity decreased from about 3.56% to about 2.92% (reduction : about 18.0%) after stirring for 1 h. With higher dosage of calcined Ca-Fe LDH, the reduction time of salinity and the increase of pH became faster, while the reduction rate of salinity was almost same and pH value increased. When the mixture was used at the mixing ratio of natural zeolite and calcined Ca-Fe LDH was 5:4, the salinity decreased to 1.0% (reduction : about 70.0%) after stirring for 1 h, and the pH of the solution increased to 9.0 - 9.7. Radish sprouts could be harvested using seawater treated with a mixture of natural zeolite and calcined Ca-Fe LDH (5 : 4), while it was not possible to harvest using seawater and seawater treated with natural zeolite with lower addition of calcined Ca-Fe LDH.

Methanol carbonylation over acid mordenite: Insights from ab initio molecular dynamics and machine learning thermodynamic perturbation theory

In this work we present a detailed ab initio study of the carbonylation reaction of methoxy groups in the zeolite mordenite, as it is the rate determining step in a series of elementary reactions leading to ethanol. For the first time we employ full molecular dynamics simulations to evaluate free energies of activation for the reactions in side pockets and main channels. Results show that the reaction in the side pocket is preferred and, when dispersion interactions are taken into account, this preference becomes even stronger. This conclusion is confirmed using multiple levels of density functional theory approximations with (PBE-D2, PBE-MBD, and vdW-DF2-B86R) or without (PBE, HSE06) dispersion corrections. These calculations, that in principle would require several demanding molecular dynamics simulations, were made possible at a minimal computational cost by using a newly developed approach that combines thermodynamic perturbation theory with machine learning.

Selective conversion of methanol to propylene over highly dealuminated mordenite: Al location and crystal morphology effects

The growing consumption of light olefins has stimulated intensive researches on methanol to olefin (MTO) process which possesses great advantages for coal conversion to value-added chemicals in an environmentally benign way. The catalysts commonly used for MTO process faces several challenges such as poor selectivity control, low hydrothermal stability and short lifetime. In the present study, we prepared a series of mordenite zeolites with variable Al contents (Si/Al molar ratios of 51−436) by a sequential dealumination treatment of air-calcination and acid leaching. The textural properties, acidity and Al location before and after the dealumination treatment have been systematically studied and their effect on MTO especially the methanol to propylene (MTP) performance was thoroughly investigated. The mordenite zeolites with the Si/Al ratios over 150 selectively catalyzed methanol conversion in the MTP pathway, providing a high propylene selectivity of 63% and propylene/ethylene ratio of > 10. Compared to the low-silica MOR catalysts, highly dealuminated MOR showed much higher stability and longer lifetime, which can be further enhanced via harsh hydrothermal pretreatment. Furthermore, the lifetime was highly related to the crystal size along c-axis. The excellent performance of highly dealuminated MOR is likely ascribed to the mesopores formed upon dealumination and the scarce Al sites located in the T sites shared by the 8-member ring (MR) side pockets and 12-MR pore channels.

Effect of Pore Connectivity of Pore-Opened Hierarchical MOR Zeolites on Catalytic Behaviors and Coke Formation in Ethanol Dehydration.

The hierarchical zeolite is one of the most promising materials for catalytic applications. However, the effect of its pore connectivity on catalytic behaviors and coke formation has not clearly been revealed. In this contribution, we demonstrate the visualization of the mesopore architecture in three-dimensional perspectives together with the pore connectivity network of pore-opened hierarchical mordenite (MOR), fabricated by the seed-assisted template-free synthesis followed by the fluoride treatment via the electron tomography (ET) technique. Interestingly, the pore-opened zeolites clearly display higher catalytic performance (approximately 80% of ethylene yield) in ethanol dehydration with respect to the parent one due to their additional pore-opened structures connected to the external surfaces of zeolites. In addition, the effect of pore connectivity network on the coke location and type obtained from ethanol conversion has been observed. It was found that the porous structure of the etched sample is directly connected to the external surface, and then, the large area of crystals can contribute to the reaction. Conversely, only a small amount of closed mesopores is observed inside the crystals in the case of the untreated sample, and therefore, the molecules cannot easily penetrate inside crystals for the catalytic reaction. These results open up promising perspectives for the development of hierarchical catalysts including fabrication by the template-free synthesis approach, pore-architecture characterization, and catalytic applications.

Raman Spectroscopic Characteristics of Zeolite Group Minerals

In this work, Raman spectroscopic experiments are conducted on zeolites, including a total of 33 varieties and seven groups with different secondary structural frameworks, for which characteristic vibration modes are studied. Most of the zeolites show prominent Raman peaks in the spectral range between 200–1200 cm−1. Different groups of zeolites can be recognized by differences in the wavenumbers of the T-O-T (T = Si and Al, O = oxygen) modes in the range 379–538 cm−1, the M-O (M = metal,) modes in the range 250–360 cm−1 and the T-O bending modes in the range 530–575 cm−1. All zeolites show characteristic Raman peaks in the range 379–529 cm−1, except for natrolite group (fibrous) zeolites, which are characterized by T-O-T modes in the 433–447 cm−1 range and T-O bending modes in the 528–538 cm−1 range. The analcime group (with singly connected four-ring chains) zeolites show T-O-T modes in the 379–392 cm−1 and 475–497 cm−1 ranges. The gismondine group (with doubly connected four-ring chains) zeolites have T-O-T modes in the 391–432 cm−1 and 463–497 cm−1 ranges. The chabazite group (with a six-cyclic ring) zeolites are characterized by M-O modes in the 320–340 cm−1 range and T-O-T modes in the 477–509 cm−1 range. The Raman modes of mordenite group zeolites (397–410 cm−1 and 470–529 cm−1) overlap with those of heulandite group zeolites (402–416 cm−1 and 480–500 cm−1). Moreover, the mordenite group has a characteristic peak in the 502–529 cm−1 range, and an additional peak in the 800–965 cm−1 range. Another recognizable peak for the heulandite group is in the 612–620 cm−1 range. The unknown zeolites (cowlesite) have unique characteristic peaks at 534 cm−1, which can aid in the verification of their identity.

Structural framework effect of various CeO2-loaded zeolites on the adsorptive removal of fipronil

Adsorption behavior of phenylpyrazole insecticide–fipronil, an endocrine disrupting compound was explored. The zeolites with microporous and mesoporous structures were modified by ion-exchange method with a cerium precursor which outlines metal oxides on the surfaces and named as Ce-beta, Ce-mordenite and Ce-13X adsorbents. They were characterized by X-ray powder diffraction, HR-TEM, BET analysis for surface area, SEM and EDS. The XPS technique was employed to verify the cerium metal exchange onto the zeolites. The batch experiments were done to investigate the effect of adsorption parameters: FIP concentration (600–1000 ppm), adsorbent dose (0.50–3.0 g/L), pH (2−11), time of contact (20–140 min), stirring speed (50–250 rpm) and temperature (25–45 °C). The equilibrium data were fitted in various adsorption isotherms and Langmuir adsorption isotherm fits properly, indicating monolayer adsorption. The best fitted pseudo-second-order model signifies a higher adsorption rate. Thermodynamics revealed the spontaneous and exothermic adsorption process. The structural comparison was also made between the 13X, Mordenite and Beta zeolite frameworks.

Ultrasonic Pretreatment as a Tool for the Preparation of Low-Defect Zeolite Mordenite.

The effects of the ultrasonic (US) pretreatment of synthesis gel for the preparation of mordenite zeolite were studied in comparison with the classical stirring method. Even though the US pretreatment was performed before the hydrothermal crystallization, it significantly affected the properties of the obtained mordenite crystals. The US-assisted procedure resulted in a material with improved textural characteristics, in particular, the micropore volume accessible for nitrogen molecules in the as-made form. On the other hand, mordenite prepared with the classical stirring method demonstrated comparable sorption properties only after a postsynthetic treatment. Moreover, in the case of US-pretreated mordenite, altered crystal shape and more homogeneous morphology were observed. 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) demonstrated that the US pretreatment introduced structural changes on the atomic level, resulting in fewer defects (reflected in the number of silanol groups) and less pore blockage (affected by Na+ cations) for the as-made sample.

Organotemplate-free synthesis of MOR zeolite from coal fly ash through simultaneously effective extraction of Si and Al

In this study, high-purity mordenite (MOR) zeolite was successfully synthesized from coal fly ash (CFA) using a simple and green method without organotemplate. The Al and Si used for MOR synthesis were simultaneously extracted from CFA, which were transformed to aluminosilicate gel by co-precipitation and then coupled with MOR seed for MOR synthesis instead of using organotemplate in common method. The results showed that the Al and Si extraction efficiencies were high, reaching up to 82.18% and 93.15%, respectively. The synthesized CFA-based MOR zeolite had a low Si/Al ratio of 3.92, and micropores is the dominating pore structure in the synthesized zeolite, accounts for up to 63.16% of its total pore volume. The possible mechanisms of MOR zeolite from CFA by gel coupling seed assisted synthesis were discussed. Furthermore, the CFA-based MOR was applied in CO 2 adsorption, heavy metal ions adsorption in aqueous solution and catalyst carrier for NH 3 -SCR reaction. The results presented that the CO 2 adsorption capacity of the CFA-based MOR was 1.92 mmol/g with high cycle stability. The removal rate of Pb 2+ was above 99.99% with Pb 2+ initial concentration of 51.30 mg/L. Mn-MOR catalyst was obtained through loading 3.36 wt% Mn by ion-exchange, which had a NO conversion rate of 93.58% at 200 °C. This study demonstrates that the gel coupling seed assisted method without organotemplate is a potential way to synthesize zeolite materials using the Si and Al simultaneously extracted from CFA. • CFA-based MOR zeolite was synthesized by an organotemplate-free method. • Al and Si were extracted from CFA with efficiencies of 82.18% and 93.15%, respectively. • Aluminosilicate gel coupling seed assisted method was used to synthesize MOR. • CFA-based MOR showed good performance in CO 2 capture, metal adsorption and NH 3 -SCR.

On the location of Lewis acidic aluminum in zeolite mordenite and the role of framework-associated aluminum in mediating the switch between Brønsted and Lewis acidity.

Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Brønsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral–tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Brønsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm−1 in the OH stretching region.