Mordenite Research Articles

Tailor-made the ultrathin nanosheet and acid site accessibility of mordenite zeolite for carbonylation of dimethyl ether

Precisely tailored nano-morphology and crystal growth endures mordenite (MOR) zeolites with reduced internal diffusion resistance, enabling greater accessibility of existing acid sites to further stimulate catalysis. Controllable synthesis nanosheet MOR zeolite thinner than 20 nm along at least one dimension is highly attractive but remains great challenge. Herein, c axis along the [001] direction shortened MOR nanosheets with a thickness of 10–20 nm was synthesized. As expected, the mass transfer performance over the nanosheet sample is significantly improved by 2.5 times compared with the conventional nano-morphology. Furthermore, more Brønsted acid sites (BAS) can be induced into 8-membered ring (8-MR) pores in the nanosheet MOR zeolite. The conversion of dimethyl ether (DME) to methyl acetate over the ultrathin MOR zeolite is increased from 17.4 % to 71.7 % compared to that of the conventional nanoparticle. The DME conversion was stable at 70.0 % after reaction 80 h, when the acid sites located in 12-membered ring pores was poisoned by the pyridine molecule. Unexpectedly, we discovered that the desorption behavior of pyridine is also influenced by the accessibility of acid site, not only by the amount of BAS in 8-MR. The unique nanosheet structure with short c axis reduces the spatial stability of pyridine adsorbed on BAS in the 8-MR side pocket and the BAS in the 8-MR side pocket can be recovered at lower temperatures. Herein, a new insight into of DME carbonylation catalyzed by ultrathin nanosheet of MOR zeolite is revealed.

Investigation of hydrogen uptake capacity for FAU, MOR, MTW, MWW

In this study, the hydrogen storage properties of various synthetic zeolites, including Zeolite Y (FAU), Mordenite (MOR), ZSM-12 (MTW), and MCM-22 (MWW) are determined at 77 K and atmospheric pressure. The structures of the zeolites are characterized by XRD, ICP-OES, FE-SEM, TGA and N2 adsorption-desorption isotherms. The results show that H-MCM-22 zeolite has the highest hydrogen storage capacity at 1.0 bar with 1.19 wt%, followed by H-MOR zeolite with 1.05 wt%, H–Y zeolite with 0.75 wt% and H-ZSM-12 zeolite with 0.60 wt%. The hydrogen adsorption data on FAU, MOR, MTW, and MWW at 77 K obey the Sips isotherm model. The experimental data show that the ultra-micropore volume of the zeolite is effective in hydrogen adsorption at low-pressure ranges. In addition, increasing the aluminum content of the zeolite increases the hydrogen adsorption capacity of the zeolite at atmospheric pressure. Therefore, zeolites with channel sizes close to the kinetic diameter of a hydrogen molecule, large cage volumes, and high aluminum content are potential candidates for energy storage applications.

Controlling copper location on exchanged MOR-type aluminosilicate zeolites for methanol carbonylation: In situ/operando IR spectroscopic studies

Replacing homogeneous catalytic processes by heterogeneous routes based on the utilization of solid catalysts is of great interest from an environmental point of view. Owing to their genuine pore structure, zeolites such as mordenites (MOR) have emerged as game-changing materials to enable the heterogenization of catalytic processes including methanol carbonylation. Cu-exchange zeolites take the edge over pristine zeolites, leading to enhanced catalytic performance in terms of greater activity, selectivity, and stability. Herein, the overall catalytic activity and stability can be modulated upon controlling the environment and location of copper active sites in zeolites. In this study, Cu-exchanged mordenites were strategically synthesized to investigate the role of Cu location inside of MOR cavities under working conditions by means of in situ/operando infrared (IR) spectroscopic studies. The results obtained revealed that a major proportion of Cu in the MR-8 cavities notably enhances the activity and stability of the catalyst. This study provides crucial insights for fine-tuning zeolite catalysts to achieve the heterogenization of homogeneous carbonylation processes.

Highly efficient photocatalyst fabricated from the recycling of heavy metal ions in wastewater for dye degradation

Water pollution and energy crisis are becoming global and strategic issues that people are closely concerned about. Green and energy-saving photocatalytic technology is developing rapidly in solving global energy crises and environmental pollution problems. Therefore, we propose the “kill two birds with one stone” strategy to design efficient photocatalysts for dye wastewater treatment by utilizing heavy metal ions in wastewater. The adsorption properties of Mordenite (MOR) were utilized to removal heavy metal ions (Cd2+ and Zn2+) from waste water, and the adsorbed heavy metal ions were dried and sulfurized to obtain CdS/ZnS/MOR(ZnCdM). Then, g-C3N4 was ultrasonically dispersed and composited with ZnCdM by self-assembly, 25 wt% ZnCdCM photocatalytic material was obtained with a degradation rate of 99.8% in 1.5 h for Rhodamine B(RhB). It was found that MOR can provid adequate support for active substances, and the surface of MOR with smaller sizes of CdS nanoparticles, ZnS nanoparticles and g-C3N4 nanosheets, which increased the specific surface area of the materials and improved the reactivity. The porous structure of MOR is favorable for the enrichment of RhB, and the electric field effect of MOR leads to the decrease of the photogenerated carrier complex rate in the semiconductor, which increases the catalytic efficiency. In addition, the double Z charge transfer mechanism formed by CdS, ZnS, g-C3N4 is favorable for separating photogenerated carriers. These synergistic effects improved the photocatalytic efficiency. This strategy will be a green and promising solution to water pollution and energy crisis.

Preparation of MOR/P(S‐co‐VPh) nanofiber composite membrane and its adsorption properties for rubidium ions

AbstractRubidium (Rb), a rare and precious metal, is widely used in high‐tech fields. In this work the structural advantages of mordenite (MOR) and group affinity of phenolic hydroxyl polymers (poly (styrene‐4‐hydroxystyrene) (P(S‐co‐VPh)) are combined to prepare MOR/P(S‐co‐VPh) nanofiber composite membranes with high selectivity and adsorption specificity for Rb+ by electrospinning. The test results show that MOR is successfully anchored on the nanofiber substrate and maintained its complete crystal structure. Adsorption experiments show that the adsorption capacity of Rb+ increases with the increase of MOR content, and pH = 9.0, T = 25°C are the best adsorption conditions. K+ shows the most obvious interference with the adsorption capacity decreased from 60.03 to 39.33 mg/g. The adsorption process follows with the Langmuir isothermal model and pseudo‐second‐order kinetic equation. The chemical adsorption based on the coordination reaction is the control step, and the intraparticle diffusion also has an important effect on the adsorption rate. The recycling test indicates that the prepared nanofiber composite membrane not only has efficient adsorption of Rb+, but also exhibits excellent regeneration and stability, which helps to achieve its widespread application and long‐term operation in harsh environments.

Preparation of Fe-HMOR with a Preferential Iron Location in the 12-MR Channels for Dimethyl Ether Carbonylation.

As the Brønsted acid sites in the 8-membered ring (8-MR) of mordenite (MOR) are reported to be the active center for dimethyl ether (DME) carbonylation reaction, it is of great importance to selectively increase the Brønsted acid amount in the 8-MR. Herein, a series of Fe-HMOR was prepared through one-pot hydrothermal synthesis by adding the EDTA-Fe complex into the gel. By combining XRD, FTIR, UV-Vis, Raman and XPS, it was found that the Fe atoms selectively substituted for the Al atoms in the 12-MR channels because of the large size of the EDTA-Fe complex. The NH3-TPD and Py-IR results showed that with the increase in Fe addition from Fe/Si = 0 to 0.02, the Brønsted acid sites derived from Si-OH-Al in the 8-MR first increased and then decreased, with the maximum at Fe/Si = 0.01. The Fe-modified MOR with Fe/Si = 0.01 showed the highest activity in DME carbonylation, which was three times that of HMOR. The TG/DTG results indicated that the carbon deposition and heavy coke formation in the spent Fe-HMOR catalysts were inhibited due to Fe addition. This work provides a practical way to design a catalyst with enhanced catalytic performance.

Modulation of aluminum species in mordenite zeolite for enhanced dimethyl ether carbonylation

Dimethyl ether (DME) carbonylation is an important intermediate step in the synthesis of methyl acetate (MA) and ethanol. H-form mordenite (MOR) can efficiently catalyze the reaction, in which Brønsted acid sites (BASs) associated with framework Al function as active sites. But the role of other Al species such as exteraframework Al (EFAl) and framework-associated Al still remains unknown. In this study, we have proposed two convenient approaches for controlling the two Al species and investigating their influence on the DME carbonylation reaction. NH3-TPD and Py-IR analyses revealed that the number of BASs increased after the removal of EFAl and the inhibition the formation of framework-associated Al. The reactivity results showed that the elimination of EFAl promoted the DME conversion from 28% to 46%. Additionally, through the implementation of in-situ calcination to impede the presence of framework-associated Al, the DME conversion increased from 28% to 50%. With the understanding that both EFAl and framework-associated Al have a detrimental effect on the reaction, the highest conversion is achieved with these two treatments, leading to 73% DME conversion with 99% selectivity to MA. Our findings provide a systematical strategy to effectively regulate the presence of Al species in zeolite, offering insights of rational design to optimize zeolite catalysts for important industrialized process.

H2-Promoted Benign Coke Strategy for Dimethyl Ether Carbonylation with Long-Term Stability and High Activity.

Zeolite-catalyzed dimethyl ether (DME) carbonylation provides a novel route to producing methyl acetate (MeOAc). Mordenite (MOR) has drawn significant interest because of its remarkable MeOAc selectivity in DME carbonylation, albeit with limited catalytic stability. Herein, novel MOR-based DME carbonylation catalysts, distinguished by long-term stability and high activity were successfully developed, based on an H2-promoted benign coke strategy. Both the H2 cofeeds and the presence of metal species with hydrogenation capability are demonstrated to be crucial for the regulation of coke depositions. The coke deposits can potentially cover the acid sites in the 12-MR main channels, thereby mitigating the occurrence of undesirable methanol-to-hydrocarbon side reactions. Meanwhile, the elimination of ultralarge coke species under the assistance of H2 and Cu species could ensure smooth mass transfer within the catalyst, contributing to its remarkable catalytic performance. The most highlighted DME carbonylation performance was achieved on coke-mediated CuZn-HMOR with a high MeOAc yield of 0.4-0.5 g·gcat-1·h-1 for over 520 h (over 50× enhancement versus HMOR), exhibiting promising industrial application potential. The current strategy is expected to inspire further research into zeolite-catalyzed reactions, which could be potentially improved by the presence of benign coke.

Designing a Mordenite Catalyst with Enhanced Acidity for Dimethyl Ether Carbonylation by Engineering Open Sn Sites

Due to their tunable acidity, shape selectivity, and excellent stability, zeolites are of great importance as solid acid materials in industrial catalysis. Tuning the properties of the acid sites in zeolites allows for the rational design and fabrication of catalysts for target reactions. Dimethyl ether (DME) carbonylation, a critical chain-growth reaction for C1 resource utilization, is selectively catalyzed by the Brønsted acid sites within the eight-membered rings (8-MRs) of mordenite (MOR). It is anticipated that strengthening the Brønsted acidity—particularly in 8-MRs—will improve the catalytic performance of MOR. In this work, density functional theory (DFT) calculations are first employed and the results used to design a modified MOR with stannum (Sn) and to predict the corresponding changes in acidity. Guided by the theoretical studies, a series of Sn-modified MOR are synthesized via a defect-engineering and subsequent heteroatom-substitution strategy. After partial desilication, isolated tetrahedral Sn species in an open configuration are successfully synthesized for the first time, within which tetrahedrally coordinated Al sites are preserved. An acidic characterization is used to confirm that the acidity of the Brønsted acid sites is enhanced by the introduction of the Sn species; as a result, the sample exhibits excellent activity in DME carbonylation reaction. Kinetic and DFT studies reveal that this strengthened acidity facilitates the adsorption of DME and reduces the activation barriers of DME dissociation and acetyl formation, accounting for the improved activity. The work demonstrates mechanistic insights into the promoting effects of strong acidity on DME carbonylation and offers a promising strategy to precisely control the acidic strength of zeolites.

Significant improvement in CH4/N2 selectivity achieved through ammonium exchange in mordenite

Adsorption-based CH4/N2 separation processes are promising and attractive, but remain a challenging task due to the lack of effective adsorbents. In this study, we present a strategy for the straightforward ammonium exchange of low-cost non-polluting sodium-type mordenite (MOR), obtaining MOR with varying ammonium contents (NH4-MOR) and exploring their effects on the CH4/N2 separation performance. The results showed that the CH4/N2 selectivity significant increase on NH4-MOR as the ammonium exchange degree increases. In particular, NH4-MOR-95 % exhibits a selectivity of CH4/N2 up to 4.6, far exceeding that of the pristine Na-MOR (1.9), while also maintaining a high level of CH4 adsorption (16.8 cm3/g) at 25 °C and 1 bar. The simulation results demonstrate that the introduction of ammonium ion significantly enhances the disparity in CH4 and N2 affinity on NH4-MOR. The breakthrough experiments confirmed that NH4-MOR has outstanding CH4/N2 separation ability. Furthermore, it was demonstrated that this exceptional separation properties of NH4-MOR are maintained at a high level even with an increased activation temperature. This fully validates the effectiveness of the ion exchange strategy and the potential applications of mordenite in the efficient CH4/N2 separation in the industry, where it was previously underutilized.

Selective removal of acid sites in mordenite with the assistance of tetraethylammonium bromide for high performing dimethyl ether carbonylation reaction

The distribution of acid sites in Mordenite (MOR) is crucial for its carbonylation performance. In this paper, MOR was subjected to acid treatment to selectively remove acid sites in 12 member-ring (MR) with the assistance of tetraethylammonium bromide (TEABr) used during synthesis process. The impact of acid treatment on structure, morphology, framework atoms and acidity were systematically studied. The characterization results indicated that the structure of the samples was only slightly impacted while the mesopore volume slightly increased. Due to the excessive removal of acid sites, the sample treated by nitric acid (0.1 mol/L) exhibited lower carbonylation activity whether with or without the protection of templates. However, the acid sites in the 12 MR were selectively removed in the citric acid treatment process by two different ways: the etching effect of H+ and the complexation of citric ions. The protection effect of templates for the acid sites in 8 MR was remarkable. Therefore, selective removal of acid sites in 12 MR was successful realized with assistance of template, leading to considerable improvements in activity for DME carbonylation reaction.

Synthesis of hierarchical mordenite by solvent-free method for dimethyl ether carbonylation reaction.

A series of hierarchical mordenite (MOR) catalysts were synthesized by adding soft templates via the solvent-free method. The influence of different kinds of soft templates on the structure, morphology and acid sites of mordenite were systematically characterized. The characterization results revealed that the addition of soft templates could successfully introduce hierarchical structure into the system while maintaining good crystallinity. The specific surface area and pore volume became larger. Surfactants could also affect the amount and distribution of acid sites, which in turn would affect the dimethyl ether carbonylation activity. Compared with cationic and nonionic surfactants, the addition of anionic surfactants such as sodium dodecyl benzene sulfonate could result in more Al species to preferentially enter into the 8 member ring, thus enhancing the amount of active sites for the carbonylation reaction while weakening the strength. Meanwhile, the addition of sodium dodecyl benzene sulfonate could also reduce the number of strong acid sites in the 12 member ring and obviously improve the carbonylation performance.

Effect of seed on synthesis of binder‐free mordenite for dimethyl ether carbonylation

AbstractA series of binder‐free mordenite (MOR) zeolites were successfully prepared by hydrothermal conversion of shaped precursors containing aluminosilicate and MOR seeds. In the synthesis of seed crystals, hexadecyltrimethylammonium bromide (CTAB) was used as a crystal growth inhibitor as well as a pore filler to adjust the morphology and introduce mesoporous pores. As a result, large aggregates, assembled nanosheets, and flowers‐like MOR were successfully synthesized with these MOR seeds. The effect of seed morphology on the performance of the binder‐free MOR was studied by scanning electron microscopy (SEM), N2 adsorption–desorption, and NH3‐TPD characterization techniques. It was found that the mesopore volume of formed MOR was positively correlated with those of the seeds. The synthesized binder‐free MOR showed high activity (0.28 g methyl acetate gcat−1 h−1), 100% selectivity, and high stability in dimethyl ether (DME) carbonylation to methyl acetate, which can be attributed to the larger surface area and more mesopores. The synthesis of MOR nano‐assemblies via this cost‐effective strategy has a wide range of potential applications.

Designing mordenite zeolites with tunable distribution of acid sites in channels and nano-morphology to boost the catalytic behavior performance of dimethyl ether carbonylation

Mordenite (MOR) zeolite is an efficient catalyst for dimethyl ether (DME) carbonylation, which a key step of indirect production of ethanol from syngas. Herein, a nanosheets MOR zeolite with an ultrathin thickness of 10–30 nm can be facilely synthesized by using a commercial cetyltrimethylammonium hydroxide agent. It greatly shortened the pore length of 8-membered ring (8-MR) side pocket and more amount of Brønsted acid sites (BAS) can be exposed. More importantly, the amount of BAS in 8-MR side pockets of the MOR zeolite can be significantly increased. It should be noted that the morphology of MOR zeolite with prismatic, nanosheets, and petal-like can be obtained and precisely regulated. As a result, the conversion of DME over the nanosheets MOR zeolite is increased by nearly 2 times. Our finding proposed a novel strategy for constructing tunable nanosized morphology MOR zeolite and simultaneously directional enrichment of BAS in 8-MR channels.

Organic molecular gate in mordenite for deep removal of acetylene and carbon dioxide from ethylene under humid condition

Adsorption-based processes for the ternary separation of CO2/C2H2/C2H4 show great potential and attractiveness, but commercialization remains a challenge due to the lack of efficient adsorbents. In this study, organic amine-modified mordenite (MOR) was developed, serving not only as a goalkeeper to accurately control ostiole and diffusion channels but also increasing the resistance to the influence of water molecules. This modification significantly improved the CO2/C2H2/C2H4 separation performance compared to pristine MOR, as evidenced by experimental and simulation results. ETA-MOR achieved excellent results in the deep purification of C2H4 from ternary CO2/C2H2/C2H4 mixtures, even under high humidity conditions. Cycling breakthrough tests demonstrated that the synthesized ETA-MOR material exhibited exceptional separation and structural stability. The obtained adsorbents exhibited excellent separation performance, thereby validating the effectiveness and potential of simple amine modification on commercially viable zeolites for industrial light hydrocarbon adsorption.

Enhancement of the dimethyl ether carbonylation activation via regulating acid sites distribution in FER zeolite framework

The carbonylation of dimethyl ether (DME) with CO is a key step for ethanol synthesis from syngas, but traditional mordenite (MOR) zeolite shows low catalytic stability. Herein, various FER zeolite nanosheets were prepared with four types of organic templates. The catalytic performance of FER in DME carbonylation is strongly dependent on the location of strong acid site in framework, which can be effectively regulated by altering organic template. FER-MORP sample synthesized with morpholine shows the highest DME conversion of 53%, thus, giving a methyl acetate space-time yield (STYMA) of 0.889mmol g-1 h-1. DFT calculation, NH3-IR, 1H/27Al/29Si MAS NMR, and in situ DRIFTS results indicate that morpholine directs more Al species, or strong Brønsted acid sites (BAS), to locate in 8-membered ring (8-MR) channels, which not only enhances carbonylation activity but also suppresses formation of coke species. The catalytic performance is well maintained within 4 repeated recycles (∼460 h).

Speciation and Reactivity Control of Cu-Oxo Clusters via Extraframework Al in Mordenite for Methane Oxidation.

The stoichiometric conversion of methane to methanol by Cu-exchanged zeolites can be brought to highest yields by the presence of extraframework Al and high CH4 chemical potentials. Combining theory and experiments, the differences in chemical reactivity of monometallic Cu-oxo and bimetallic Cu-Al-oxo nanoclusters stabilized in zeolite mordenite (MOR) are investigated. Cu-L3 edge X-ray absorption near-edge structure (XANES), infrared (IR), and ultraviolet-visible (UV-vis) spectroscopies, in combination with CH4 oxidation activity tests, support the presence of two types of active clusters in MOR and allow quantification of the relative proportions of each type in dependence of the Cu concentration. Ab initio molecular dynamics (MD) calculations and thermodynamic analyses indicate that the superior performance of materials enriched in Cu-Al-oxo clusters is related to the activity of two μ-oxo bridges in the cluster. Replacing H2O with ethanol in the product extraction step led to the formation of ethyl methyl ether, expanding this way the applicability of these materials for the activation and functionalization of CH4. We show that competition between different ion-exchanged metal-oxo structures during the synthesis of Cu-exchanged zeolites determines the formation of active species, and this provides guidelines for the synthesis of highly active materials for CH4 activation and functionalization.

Methane Oxidation over Cu2+/[CuOH]+ Pairs and Site‐Specific Kinetics in Copper Mordenite Revealed by Operando Electron Paramagnetic Resonance and UV/Visible Spectroscopy

AbstractCu‐exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu‐MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet‐visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier‐transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired [CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent [CuOH]+ demonstrates that the frequently reported assumption of redox‐inert Cu2+ centers does not generally apply. The measured site‐specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential.

Methane Oxidation over Cu2+ /[CuOH]+ Pairs and Site-Specific Kinetics in Copper Mordenite Revealed by Operando Electron Paramagnetic Resonance and UV/Visible Spectroscopy.

Cu-exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu-MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet-visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired [CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent [CuOH]+ demonstrates that the frequently reported assumption of redox-inert Cu2+ centers does not generally apply. The measured site-specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential.

Size Effect on Diffusion and Catalytic Performance of Mordenite in Dimethyl Ether Carbonylation

The carbonylation of dimethyl ether (DME) to produce methyl acetate (MA) has a promising prospect in industry. Mordenite (MOR) has been widely studied due to its excellent catalytic activity and high MA selectivity; however, its microporous characteristic limits the intracrystalline diffusion that influences the activity and stability. Therefore, it becomes essential to clarify the relationship between catalytic activity and diffusion. In this study, a series of MOR samples with similar Si/Al contents and aspect ratios, but different sizes, were successfully synthesized by adjusting the synthesis parameters (Si/Al contents in gel, aging time, the amount of water, and alkalinity). Based on quantitative analysis of acid properties and catalyst evaluation, both the apparent turnover frequency of MA (TOFMA) and the stability decrease with the increase in particle size. Diffusion parameter measurements and kinetic analysis via zero length column methods show that the intracrystalline diffusion restriction becomes more serious with increasing particle size. The larger the MOR crystals with enhanced mass transfer limitation that undergo lower activity, the higher the selectivity of byproducts, as well as the faster their deactivation.