Mordenite Zeolite Research Articles

Comparison of surface passivation modification of two mordenite zeolites and their application on the isomerisation of o-ethyltoluene.

During the isomerisation of o-ethyltoluene (O-ET) to produce m-ethyltoluene (M-ET) and p-ethyltoluene (P-ET), it is crucial to improve the isomerisation selectivity and reduce side reactions, such as disproportionation, alkyl transfer, and splitting. In this study, in order to improve the selectivities toward M-ET and P-ET during O-ET isomerisation, both the commercial micropore mordenite (HM) and the prepared micro-mesoporous mordenite (HM-M) were treated through chemical liquid deposition using tetraethyl orthosilicate (TEOS) and 3,5-dimethylphenylmagnesium bromide (DPB), respectively. Thereafter, their structure, porosity, and acidity were characterized via X-ray diffraction, transmission electron microscopy, inductively coupled plasma, N2 sorption, temperature-programmed desorption of ammonia, Fourier-transform infrared spectroscopy of pyridine and 2,6-di-tert-butylpyridine, and thermal analysis. The deposition mechanism of DPB was also discussed. The results showed that TEOS could shrink and block the micropores of mordenite. By contrast, DPB passivated the external surface acidity and did not affect the micropore structure. Moreover, HM modified using DPB significantly shortened the self-coking process, improved the product selectivities for M-PT and P-ET as well as their stability, and prolonged the catalytic life. When the amount of magnesium oxide (MgO) deposited on the HM zeolite was 4%, the product selectivities toward M-ET and P-ET increased from 67.27% to 77.54%, and the yields of M-ET and P-ET increased from 47.57% to 52.98%. However, the performance of the catalyst was not significantly enhanced on the HM-M, owing to the passivation of acidic sites in the mesopores by the TEOS and DPB.

K2O SUPORTADO EM ZEÓLITA NATURAL: SÍNTESE, CARACTERIZAÇÃO E APLICAÇÃO PRODUÇÃO DE BIODIESEL A PARTIR DO ÓLEO DE GIRASSOL

K2O SUPPORTED ON NATURAL ZEOLITE: SYNTHESIS, CHARACTERIZATION AND APPLICATION OF BIODIESEL PRODUCTION FROM SUNFLOWER OIL. Biodiesel is a renewable fuel, a substitute for fossil diesel, which is important for reducing GHG in Brazil. Therefore, this work aims to synthesize and characterize the catalyst using the support of natural zeolite impregnated with K2O and apply it in the production of biodiesel through the transesterification reaction. Through the analysis of characterizations such as XRD, characteristic peaks of Clinoptilolite and Mordenite zeolites were verified in the natural zeolite, in addition to evidencing the characteristic peaks of KI and K2O in this microporous support. Thermal and FTIR analyzes revealed the presence of KI and K2O in the presence of the decomposition region of composite compounds (500 to 800 °C) and corresponding vibration bands, while EDS analysis indicated the efficiency of KI to K2O conversion after calcination. To evaluate the application of the catalyst in the production of biodiesel, the following reaction conditions were studied: percentage of catalyst in relation to oil mass (6% and 8%), methanol:oil mass ratio (15: 1 and 30: 1) and temperature (60 °C and 90 °C). The catalyst presents good results reaching a conversion of 98.96% in esters using 6% catalyst, mass ratio oil:methanol 1:30 and reaction temperature of 90 °C.

THE DISMUTATION OF TOLUENE TO BENZENE AND XYLENES OVER H-MORDENITE ZEOLITE

Synthetic and natural mordenite zeolites were decationized (DC) and dealuminized (DA) with different concentrations of HCl, and the catalyst samples were subjected to X-ray phase analysis. Over the samples of the catalyst was carried out the dismutation of toluene to benzene and xylene in the temperature range of 300-380 °C. It has been established that H-mordenite catalysts in the range SiO2/Al2O3 = 17-20 are more active and selective in the reaction under study conditions. It has been shown that synthetic mordenite zeolite has a higher activity than natural mordenite zeolite.

Facile synthesis of nanosized mordenite and beta zeolites with improved catalytic performance: non-surfactant diquaternary ammonium compounds as structure-directing agents

Nanosized MOR and BEA zeolites were directly synthesized using simple diquaternary ammonium compounds. The nanosized zeolites show improved catalytic performance in Friedel–Crafts and n-alkane hydroconversion reactions.

Global optimization of extraframework ensembles in zeolites: structural analysis of extraframework aluminum species in MOR and MFI zeolites.

Metal-modified zeolites are versatile catalytic materials with a wide range of industrial applications. Their catalytic behaviour is determined by the nature of externally introduced cationic species, i.e., its geometry, chemical composition, and location within the zeolite pores. Superior catalyst designs can be unlocked by understanding the confinement effect and spatial limitations of the zeolite framework and its influence on the geometry and location of such cationic active sites. In this study, we employ the genetic algorithm (GA) global optimization method to investigate extraframework aluminum species and their structural variations in different zeolite matrices. We focus on extraframework aluminum (EFAl) as a model system because it greatly influences the product selectivity and catalytic stability in several zeolite catalyzed processes. Specifically, the GA was used to investigate the configurational possibilities of EFAl within the mordenite (MOR) and ZSM-5 frameworks. The xTB semi-empirical method within the GA was employed for an automated sampling of the EFAl-zeolite space. Furthermore, geometry refinement at the density functional theory (DFT) level of theory allowed us to improve the most stable configurations obtained from the GA and elaborate on the limitations of the xTB method. A subsequent ab initio thermodynamics analysis (aiTA) was chosen to predict the most favourable EFAl structure(s) under the catalytically relevant operando conditions.

Tuning the catalytic acidity in Al2O3 nanofibers with mordenite nanocrystals for dehydration reactions.

Alumina (Al2O3) is one of the most used supports in the chemical industry due to its exceptional thermal stability, surface area, and acidic properties. Mesoscopic structured alumina with adequate acidic properties is important in catalysis to enhance the selectivity and conversion of certain reactions and processes. This study introduces a synthetic method based on electrospinning to produce Al2O3 nanofibers (ANFs) with zeolite mordenite (MOR) nanocrystals (hereafter, hybrid ANFs) to tune the textural and surface acidity properties. The hybrid ANFs with electrospinning form a non-woven network with macropores. ANF-HMOR, i.e., ANFs containing protonated mordenite (HMOR), shows the highest total acidity of ca. 276 μmol g−1 as determined with infrared spectroscopy using pyridine as a molecular probe (IR-Py). IR-Py results reveal that Lewis acid sites are prominently present in the hybrid ANFs. Brønsted acid sites are also observed in the hybrid ANFs and are associated with the HMOR presence. The functionality of hybrid ANFs is evaluated during methanol dehydration to dimethyl ether (DME). The proof of concept reaction reveals that ANF-HMOR is the more active and selective catalyst with 87% conversion and nearly 100% selectivity to DME at 573 K. The results demonstrate that the textural properties and the acid site type and content can be modulated in hybrid ANF structures, synergistically improving the selectivity and conversion during the methanol dehydration reaction. From a broader perspective, our results promote the utilization of hybrid structural materials as a means to tune chemical reactions selectively.

Synthesis of Zinc(II)-natural zeolite mordenite type as a drug carrier for ibuprofen: Drug release kinetic modeling and cytotoxicity study

Zn(II)-ZMT material development based on natural zeolite mordenite type (ZMT) as a drug carrier for ibuprofen has been explored and assessed. The ion exchange method was carried out to prepare Zn(II)-ZMT material. XRD, FTIR, and FESEM-EDS were used to characterize the physico-chemical characteristics of all materials. The performance of Zn(II)-ZMT as a drug delivery agent for ibuprofen was also evaluated using drug loading-release, zeta potential measurement, and cytotoxicity testing. Six kinetic models (including the zero-order, first-order, Peppas-Sahlin, Higuchi, Hixson-Crowell, and Korsmeyer-Peppas models) were utilized to simulate the drug release process. Meanwhile, a microtetrazolium (MTT) assay was used to analyze the material's cytotoxicity. The Zn(II)-ZMT material has a drug loading content (DLC) of 90.37 % and an efficiency entrapment content (EEC) of 54.22 %, according to drug loading. The drug releases kinetic modeling of Ibuprofen from Zn(II)-ZMT followed the Hixson-Crowell model. This material exhibits good biocompatibility based on a cytotoxicity test using the MTT assay. Ibu@Zn(II)-ZMT has a zeta potential of − 61.55 mV ± 0.1 mV. These findings suggest that the material in the dispersion system has a high degree of stability, indicating that it will not flocculate or coagulate in the body. Furthermore, Zn(II)-ZMT is an inorganic substance that has the potential to be employed as a medication delivery material in the future.

Improvement of esterification conversion by rapid pervaporation dehydration using a high-flux and acid-resistant MOR zeolite membrane

Esterification coupled with pervaporation (PV) is an effective method to improve conversion by thoroughlyand rapidly removing the water product. In this study, a high-flux and acid-resistant mordenite (MOR) zeolite membrane was applied to enhance the esterification of acetic acid and ethanol. The effects of catalysts, catalyst loading, reaction temperature and initial acid/alcohol molar ratio on the conversion of ethanol for the esterification with PV were investigated systematically. Results showed that a high conversion (99.3%) was obtained in a short reaction time of 480 min when the operating conditions were optimized as reaction temperature of 353 K, concentrated H2SO4 catalyst loading of 0.1 wt% and initial acid/alcohol molar ratio of 1.5:1. The conversion of esterification without PV reached equilibrium was 76.7% but enhanced to 99.3% with PV in 480 min. The conversion of ethanol was up to 98.4% even at a low initial acid/alcohol molar ratio of 1.2:1. Importantly, the membrane showed good acidic stability in the esterification with PV after 8 reaction cycles. Thus through the coupling of PV and esterification, the conversion of ethanol was greatly improved due to the water from esterification was removed timely. On the other hand, the usage of acetic acid could be reduced, which enormously decreased the energy consumption in the production process.

A green synthesis of MOR zeolite membranes by wet gel conversion for dehydration of water-acetic acid mixtures

High performance mordenite (MOR) membranes were successfully synthesized by wet gel conversion (WGC) route using organic template-free and fluoride-free gels on seeded macroporous Al2O3 tubes. The seeded Al2O3 tubes were dipped into the gel solution with a composition of SiO2: 0.0045Al2O3: 0.19 Na2O: 27.76 H2O and then directly crystallized at 150 °C for 8 h without any extra solvent or solution in autoclave. The concentration of MOR seeds, crystallization time, composition of gels and crystallization way (hydrothermal growth or WGC) significantly influenced the membrane performance for dehydration of acetic acid (AA) mixtures by pervaporation. The prepared MOR membranes displayed a high water flux and good selectivity in long-term dehydration of 90 wt.% AA/H2O at 75 °C with the steay-state flux of 0.70 kg m−2 h−1 and separation factor increasing to 5000 after 200 h test. The WGC approach reduced the consumption of gel by about 96% with almost “zero” waste liquid. This WGC method is demonstrated as an efficient, green route to synthesze zeolite membranes and to possess potentiality for industrial dehydration applications.

Cover Feature: DFT Analysis of Methane C−H Activation and Over‐Oxidation by [Cu2O]2+ and [Cu2O2]2+ Sites in Zeolite Mordenite: Intra‐ versus Inter‐site Over‐Oxidation (ChemPhysChem 24/2021)

The Cover Feature illustrates the inter-site nature of methane over-oxidation by dicopper sites in zeolites used for direct methane-to-methanol conversion. Intermediates from methane oxidation can be stabilized at the immediate active site or at Brønsted acid sites, without over-oxidation. This ensures high methanol selectivities. More information can be found in the Article by Samuel O. Odoh and co-workers.

Mordenite zeolite for scavenging nitroxide radicals and its effect on the thermal decomposition of nitrocellulose

ABSTRACT Nitrogen oxides (NO x ), which result from the decomposition of nitrocellulose (NC)-based solid propellants, promote the degradation of this later and alter its long-term stability. Thus, to avoid such situation and ensure a better stability, conventional stabilizers such as aromatic amines or urea compounds are usually added to the NC-based formulations. However, these latter may generate carcinogenic and toxic species that may negatively affect both human health and environment. Herein, based on its selective adsorption capacity of NO x , the stability potential of a porous inorganic compound, namely, mordenite (MOR), on nitrocellulose was assessed. Three NC-based samples (S1–S3) were prepared through the incorporation of 3 wt.% of stabilizing agents, i.e., S1: pure NC, S2: NC + DPA, and S3: NC + MOR. The effect on the stability of this inorganic compound with regard to pure NC has been highlighted utilizing stability tests and kinetic modeling. Beforehand, the compatibility of mordenite with nitrocellulose was initially checked by means of DSC and FTIR. Furthermore, the obtained results via Vacuum Stability Test (VST) and Bergmann–Junk (B&J) test demonstrated that S3 displayed a better stability than S1 and comparable behavior to S2. The determination of the kinetic triplet by isoconversional methods confirmed the effectiveness of MOR as a stabilizing agent. These findings claim that such inorganic compound may be used efficiently as a stabilizer for NC-based energetic formulations.

Copper Pairing in the Mordenite Framework as a Function of the CuI /CuII Speciation.

A series of gas‐phase reactants is used to treat a Cu‐exchanged mordenite zeolite with the aim of studying the influence of the reaction environment on the formation of Cu pairs. The rearrangement of Cu ions to form multimeric sites as a function of their oxidation state was probed by X‐ray absorption spectroscopy (XAS) and also by applying advanced analysis through wavelet transform, a method able to specifically locate Cu–Cu interactions also in the presence of overlapping contributions from other scattering paths. The nature of the Cu‐oxo species formed upon oxidation was further crosschecked by DFT‐assisted fitting of the EXAFS data and by resonant Raman spectroscopy. Altogether, the CuI/CuII speciation clearly correlates with Cu proximity, with metal ion pairs quantitatively forming under an oxidative environment.

Copper Pairing in the Mordenite Framework as a Function of the CuI/CuII Speciation

AbstractA series of gas‐phase reactants is used to treat a Cu‐exchanged mordenite zeolite with the aim of studying the influence of the reaction environment on the formation of Cu pairs. The rearrangement of Cu ions to form multimeric sites as a function of their oxidation state was probed by X‐ray absorption spectroscopy (XAS) and also by applying advanced analysis through wavelet transform, a method able to specifically locate Cu–Cu interactions also in the presence of overlapping contributions from other scattering paths. The nature of the Cu‐oxo species formed upon oxidation was further crosschecked by DFT‐assisted fitting of the EXAFS data and by resonant Raman spectroscopy. Altogether, the CuI/CuII speciation clearly correlates with Cu proximity, with metal ion pairs quantitatively forming under an oxidative environment.

DFT Analysis of Methane C-H Activation and Over-Oxidation by [Cu2 O]2+ and [Cu2 O2 ]2+ Sites in Zeolite Mordenite: Intra- versus Inter-site Over-Oxidation.

Methane over-oxidation by copper-exchanged zeolites prevents realization of high-yield catalytic conversion. However, there has been little description of the mechanism for methane over-oxidation at the copper active sites of these zeolites. Using density functional theory (DFT) computations, we reported that tricopper [Cu3 O3 ]2+ active sites can over-oxidize methane. However, the role of [Cu3 O3 ]2+ sites in methane-to-methanol conversion remains under debate. Here, we examine methane over-oxidation by dicopper [Cu2 O]2+ and [Cu2 O2 ]2+ sites using DFT in zeolite mordenite (MOR). For [Cu2 O2 ]2+ , we considered the μ-(η2 :η2 ) peroxo-, and bis(μ-oxo) motifs. These sites were considered in the eight-membered (8MR) ring of MOR. μ-(η2 :η2 ) peroxo sites are unstable relative to the bis(μ-oxo) motif with a small interconversion barrier. Unlike [Cu2 O]2+ which is active for methane C-H activation, [Cu2 O2 ]2+ has a very large methane C-H activation barrier in the 8MR. Stabilization of methanol and methyl at unreacted dicopper sites however leads to over-oxidation via sequential hydrogen atom abstraction steps. For methanol, these are initiated by abstraction of the CH3 group, followed by OH and can proceed near 200 °C. Thus, for [Cu2 O]2+ and [Cu2 O2 ]2+ species, over-oxidation is an inter-site process. We discuss the implications of these findings for methanol selectivity, especially in comparison to the intra-site process for [Cu3 O3 ]2+ sites and the role of Brønsted acid sites.

The efficiency of zeolites in water treatment for combating ammonia – An experimental study on Yamuna River water & treated sewage effluents

This study was meant to study the effectiveness of natural and synthetic zeolites in water treatment for combating ammonia nitrogen so that specific zeolites could be utilized at waterworks and sewage disposal works. In this study, three different zeolites were utilized in their pristine state, namely natural clinoptilolite, natural mordenite, and synthetic zeolites 4A. We examined the zeolites for their ammonia removal capacity. We performed experimental studies on synthetically prepared ammonia water, the Yamuna River water, and municipally treated sewage effluents by using Jar Test Apparatus at 100 RPM. Ammonia nitrogen content was determined by nesslerization standard method using a spectrophotometer. It has been observed that all zeolites are significantly effective in treating ammonia nitrogen in artificially prepared ammonia nitrogen water without having competing ions interference. However, because competing ions interfere in natural water, its use limits ammonium ions removal. Based on the present study outcomes, the authors have suggested replacing sand media from Rapid Sand Filters and Slow Sand Filters with Mordenite and Clinoptilolite at municipal water treatment utilities to combat low amounts of ammonium ions.

Utilization of Modified Zeolite as Catalyst for Steam Gasification of Palm Kernel Shell

Syngas from biomass gasification is being developed for alternative feedstock in the chemical industry. Palm kernel shell which is generated from palm oil industry can be potentially used as raw material for gasification process. The purpose of this study was to investigate the use of modified natural zeolite catalysts in steam gasification of palm kernel shells. Mordenite type zeolite was modified by acid leaching to be used as a tar cracking catalyst. Steam gasification was conducted at the temperature range of 750–850 °C and the steam to biomass ratio was in the range of 0–2.25. The result showed that steam gasification of palm kernel shell with the addition of zeolite catalyst at 750 °C and steam to biomass ratio 2.25 could reduce tar content up to 98% or became 0.7 g/Nm3. In this study, gasification of palm kernel shells produced syngas with the hydrogen concentration in the range of 52–64% and H2/CO ratio of 2.7–5.7. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Solution-mediated transformation of natural zeolite to ANA and CAN topological structures with altered active sites for ethanol conversion

In this study, one-pot syntheses of cancrinite (CAN) and analcime (ANA) frameworks from mordenite (MOR) natural zeolite were performed for the first time. The effects of the synthesis gel composition and alkalinity on the phase formation and crystallinity of the product were investigated. All studied zeolites were evaluated for their catalytic activities in ethanol conversion reactions from 473 K to 673 K and at 1 atm. The results suggested that the formation pathways of CAN and ANA are highly dependent on the alkalinity of the synthesis solution and the type of starting material regardless of synthesis template. The use of natural MOR zeolite (MORNZ) in the synthesis can contribute to highly crystalline ANA structures comparable to the ANA products obtained from fumed silica and sodium aluminate (NaAlO2). The quantity and locations of the acidic-cationic dual active sites of the proton-form product zeolites are suitable for synthesizing acetaldehyde from ethanol with over 90% product selectivity. However, further development of synthesis procedures to enhance the surface area is needed to improve the ethanol conversion of the resulting zeolites. This work provides a new perspective on highly crystalline and pure-phase zeolitic structural formations from natural zeolite and their potential application in ethanol conversion.

Supercritical ion exchange: A new method to synthesize copper exchanged zeolites

A new technique termed Supercritical Ion Exchange (SCIE) was developed and used to synthesize Cu-mordenite (Cu-MORS). The ion exchange takes place between the Cu complex (Copper(II)trifluoroacetylacetonate) dissolved in supercritical CO2 (scCO2) and the extraframework protons in mordenite zeolite without requiring an aqueous phase. The occurrence of the ion exchange reaction was demonstrated by using 1H NMR analysis of the high-pressure fluid phase samples and by visual inspection of the fluid phase color change during the synthesis. SCIE resulted in selective ion-exchange inferred by the equilibrium isotherm. The prepared catalysts were used for the stepwise direct methane to methanol (sDMTM) process and results showed that methanol productivity increased linearly with increasing Cu loading up to a certain Cu wt%. Cu-MORS displayed 16% higher methanol productivity as compared to Cu-MORA (prepared by aqueous ion exchange) with the same Cu loading. The results demonstrated the importance of site selective ion-exchange for zeolite catalysis.

Local Structure of Copper Centers Obtained during Solid-Phase Synthesis in Copper–Mordenite Zeolite

Local Structure of Copper Centers Obtained during Solid-Phase Synthesis in Copper–Mordenite Zeolite

Self-assembled iron-containing mordenite monolith for carbon dioxide sieving.

The development of low-cost, efficient physisorbents is essential for gas adsorption and separation; however, the intrinsic tradeoff between capacity and selectivity, as well as the unavoidable shaping procedures of conventional powder sorbents, greatly limits their practical separation efficiency. Herein, an exceedingly stable iron-containing mordenite zeolite monolith with a pore system of precisely narrowed microchannels was self-assembled using a one-pot template- and binder-free process. Iron-containing mordenite monoliths that could be used directly for industrial application afforded record-high volumetric carbon dioxide uptakes (293 and 219 cubic centimeters of carbon dioxide per cubic centimeter of material at 273 and 298 K, respectively, at 1 bar pressure); excellent size-exclusive molecular sieving of carbon dioxide over argon, nitrogen, and methane; stable recyclability; and good moisture resistance capability. Column breakthrough experiments and process simulation further visualized the high separation efficiency.