Search

Hydrogen sulfide (H2S) is a hazardous gas found in natural gas and biogas, lethal over 100 ppm. When released into the atmosphere, it can turn into sulfur dioxide. One option to remove H2S is using porous materials such as zeolites. Among them, mordenite stands out due to its channel structure, wide availability, and low cost. In this work, we evaluated the H2S adsorption capacity of mordenite using a volumetric static method. The results show the adsorption capacity of H2S in mordenite varies with the exchanged cation. The highest was measured in Na‐mordenite (~4.08 mmol H2S/g mordenite). The experimental breakthrough curves for this zeolite confirmed Langmuir‐type adsorption and strong affinity between Na+ cations and H2S. Despite this interaction, the XRD diffractograms of Na‐mordenite show that the material retained its crystalline structure. More information about the differences in the amount of H2S adsorbed in the zeolites caused by the change in exchanged cation was obtained by H2S adsorption followed by FTIR spectroscopy. The spectra show differences in the position of the peaks related to the different adsorption modes of H2S caused by a change in the polarizing power of the cations due to their charge and position inside the zeolite pores. [ABSTRACT FROM AUTHOR]

The insufficiency of freshwater supplies has posed a serious threat to sustainable socioeconomic growth, and seawater desalination is considered to be the most promising solution to alleviate such pressure. Currently, 2D carbon membranes are identified as deserving candidates due to their high permeability and multiple tunable properties. However, they remain challenging to systematically uncover the potential relationships between structures and properties in various 2D carbon materials. For this, a machine learning (ML) model based on feature datasets of 2D carbon materials effecting desalination properties is trained. The results suggest that structures with a maximum pore size of 10–12 atoms and atomic densities between 0.28 and 0.41 are more likely to achieve high properties. Cml‐MOR based on MOR‐type mordenite zeolite for validation is selected. Further, Cml‐MOR is demonstrated to feature remarkable salt ion adsorption. The effective water flux of Cml‐MOR is 113.51 L cm−2 day−1 MPa−1, and the salt rejection at 110 MPa can reach 98.9%. This work is expected to apply this efficient method to investigate the structure and properties of 2D carbon membranes with great structural diversity; this will attract more people to focus on them and explore their important potential for practical applications. [ABSTRACT FROM AUTHOR]

A 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. [ABSTRACT FROM AUTHOR]

BACKGROUND: Grand efforts have been recently devoted to the development of catalysts based on the excellent performance of Cu‐ and Fe‐dependent enzymes in methanotrophic bacteria for the partial oxidation of methane to methanol under ambient conditions. As a continuation of the study on the stepwise manner for this conversion over zeolite‐based catalysts, in this work, the effects of zeolite topology and activation temperature on the catalytic performance of Cu‐ and Fe‐containing zeolites were investigated. RESULTS: Cu species exchanged in the medium‐pore zeolites (mordenite, ZSM‐5, and ferrierite) afforded better methanol production, while large‐pore zeolites (zeolite β and zeolite γ) were inappropriate to accommodate active Cu sites. Notably, Cu/silicalite‐1 containing CuO species was also reactive to methane after the activation in O2, yielding a minor methanol amount. Furthermore, the activity of Fe/mordenite towards the methanol in the O2‐assisted procedure was reported for the first time but with a much lower yield as compared to that of Cu/mordenite. The methanol yield over Cu/mordenite increased with the activation temperature because increasing the activation temperature favored the Cu‐exchange degree with a higher priority at the side pockets as compared to the main channels of mordenite, as evidenced from infrared analysis. CONCLUSION: The selective oxidation of methane to methanol by O2 via a stepwise manner can be obtained over both ion‐exchanged Cu species and well‐dispersed CuO nanoparticles with better activity being recorded for the former. The activity of Cu‐exchanged zeolites was considerably dependent on the zeolite topology and the charge‐balancing position of the Cu2+ cations. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Copper(II)‐containing mordenite (CuMOR) is capable of activation of C−H bonds in C1‐C3 alkanes, albeit there are remarkable differences between the functionalization of ethane and propane compared to methane. The reaction of ethane and propane with CuMOR results in the formation of ethylene and propylene, while the reaction of methane predominantly yields methanol and dimethyl ether. By combining in situ FTIR and MAS NMR spectroscopies as well as time‐resolved Cu K‐edge X‐ray absorption spectroscopy, the reaction mechanism was derived, which differs significantly for each alkane. The formation of ethylene and propylene proceeds via oxidative dehydrogenation of the corresponding alkanes with selectivity above 95 % for ethane and above 85 % for propane. The formation of stable π‐complexes of olefins with CuI sites, formed upon reduction of CuII‐oxo species, protects olefins from further oxidation and/or oligomerization. This is different from methane, the activation of which proceeds via oxidative hydroxylation leading to the formation of surface methoxy species bonded to the zeolite framework. Our findings constitute one of the major steps in the direct conversion of alkanes to important commodities and open a novel research direction aiming at the selective synthesis of olefins. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Part of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High‐field 27Al NMR data show that more framework Al atoms at T3 and T4 sites change geometry to nonframework structures than others. These nonframework Al species preferentially reside in the side pockets, which will decrease the accessibility of acid sites in the 8‐membered ring (MR) channel, impairing the dimethyl ether (DME) carbonylation reaction. The arisen octahedrally coordinated Al species are framework‐associated, which can be reverted into the zeolite framework. Herein, we find that a facile treatment with pyridine could force the octahedral coordination Al back into a tetrahedral environment, which could increase the number of available active sites and enhance the diffusion of DME, thus improving the reactivity (4 times) of the DME carbonylation reaction and prolonging the lifetime of catalysts. [ABSTRACT FROM AUTHOR]

The selective conversion of methane to high value‐added chemicals under mild conditions is of great significance for the commercially viable and sustainable utilization of methane but remains a formidable challenge. Herein, we report a strategy for efficiently converting methane to acetic acid via CH3Cl as an intermediate. Up to 99.3 % acetic acid and methyl acetate (AA+MA) selectivity was achieved over pyridine‐pretreated MOR (MOR‐8) under moderate conditions of 523 K and 2.0 MPa. Water, conventionally detrimental to carbonylation reaction over zeolite catalysts, was conducive to the production of AA in the current reaction system. In the 100 h continuous test with the MOR‐8 catalyst, the average AA+MA selectivity remained over 98 %. AA was formed by carbonylation of methoxy groups within 8‐membered rings of MOR followed by hydrolysis. This strategy provided an approach for highly efficient utilization of methane to oxygenates under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Nanocrystalline mordenite (MOR) zeolites were hydrothermally synthesized in a single step with commercial cetyltrimethylammonium (CTA) hydroxide as the sole organic template, while the aluminum source was varied in a typical synthesis gel. CTA can effectively reduce the crystal growth of MOR zeolites, in some cases selectively in the a‐ and b‐directions of the unit cell. These nanocrystalline MOR zeolites do not only have a larger external surface area than their bulk counterparts prepared without CTA, but the Brønsted acid sites in the side‐pockets are also more accessible. The combination of the use of CTA and AlCl3 ⋅ 6H2O afforded the best‐performing catalyst with much improved activity in benzene alkylation and hydroconversion of n‐hexadecane (n‐C16). Modifying MOR synthesis with CTA hydroxide is a cheap and effective method to open up the one‐dimensional micropore system of mordenite, increasing the catalytic performance in hydrocarbon reactions. [ABSTRACT FROM AUTHOR]

Controlling the location of aluminum atoms in a zeolite framework is critical for understanding structure–performance relationships of catalytic reaction systems and tailoring catalyst design. Herein, we report a strategy to preferentially relocate mordenite (MOR) framework Al atoms into the desired T3 sites by low‐pressure SiCl4 treatment (LPST). High‐field 27Al NMR was used to identify the exact location of framework Al for the MOR samples. The results indicate that 73 % of the framework Al atoms were at the T3 sites after LPST under optimal conditions, which leads to controllably generating and intensifying active sites in MOR zeolite for the dimethyl ether (DME) carbonylation reaction with higher methyl acetate (MA) selectivity and much longer lifetime (25 times). Further research reveals that the Al relocation mechanism involves simultaneous extraction, migration, and reinsertion of Al atoms from and into the parent MOR framework. This unique method is potentially applicable to other zeolites to control Al location. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Aging effects of off‐gas streams including dry air and humid air on reduced silver exchanged mordenite (Ag0Z) were studied. Aged Ag0Z was prepared by exposing Ag0Z to dry air and humid air at different aging temperatures, time, and water vapor concentrations. Iodine loading capacity on the aged Ag0Z was obtained through a continuous‐flow adsorption system. Significant iodine loading capacity losses were observed after the Ag0Z was exposed to dry air and humid air. Physical and chemical analyses were conducted to observe the physical and chemical changes of Ag0Z after being aged. From iodine adsorption data and sample analyses, it was found that iodine loading capacity on the aged Ag0Z in dry air and humid air decreases with increasing aging temperatures, time, and water vapor concentrations. The pseudo reaction model describes experimental data well and the oxidation of Ag0 is the rate determining step in the aging process. [ABSTRACT FROM AUTHOR]

In the methanol‐to‐olefins (MTO) reaction, product flexibility is important for meeting the fluctuating chemicals demands. In this paper, the catalytic performance of recently reported zeolites having 12‐ring pores, such as boroaluminosilicate CON‐type zeolite ([Al,B]‐CON), MCM‐68, and YNU‐5 zeolites, in the MTO reaction was compared to understand the relationship between zeolite framework and product selectivity. The catalytic performance of the synthesized zeolites was compared with that of Beta, mordenite, and ZSM‐5. The highest selectivities for propylene and butylenes were achieved over MCM‐68. The highest propylene‐to‐ethylene ratio in the products was obtained over [Al,B]‐CON. ZSM‐5 and [Al,B]‐CON exhibited a superior ability to suppress coke formation compared to Beta, mordenite, MCM‐68, and YNU‐5. [ABSTRACT FROM AUTHOR]

As it is well known, Brønsted acid sites in 8‐MR of H‐MOR (mordenite) are selective for dimethyl ether (DME) carbonylation to methyl acetate, whereas those in 12‐MR are more prone to methanol to olefin reaction. Interestingly, we observed that the Brønsted acid sites in 12‐MR of H‐MOR are highly active for dimethoxymethane (DMM) carbonylation to methyl methoxyacetate (MMAc), whereas those in 8‐MR led to the formation of DME. A series of modified H‐MOR catalysts with accurate regulation of Brønsted acid sites in 12‐MR or 8‐MR were successfully synthesized by selective Na+ exchange or pyridine (Py) adsorption. Fourier‐transform infrared (FT‐IR) spectra, NH3‐temperature‐programmed desorption, Py‐FT‐IR, and inductively coupled plasma analyses suggested that Na+ first occupied Brønsted acid sites in 8‐MR and then replaced those in 12‐MR. All Na+‐exchanged catalysts exhibited significant acceleration on MMAc selectivity, and the ratio of Brønsted acid amount in 12‐MR/total had a positive correlation with MMAc selectivity. The MMAc selectivity (78%) of H‐MOR‐0.15Na was nearly 2.5 times more than that of untreated H‐MOR (31%). However, H‐MOR‐Py showed almost no carbonylation activity (<1% MMAc) and a highest DME selectivity (98%), indicating that Brønsted acid sites in 12‐MR were the only active sites for DMM carbonylation, whereas those in 8‐MR tended to accelerate DMM disproportionation to DME. [ABSTRACT FROM AUTHOR]

This work analyzes the preparation and antifungal behavior of composite films formed by a mixed matrix of Ag‐zeolite crystals immobilized in a continuous polymer phase. The physicochemical qualities of films prepared with Ag‐exchanged mordenite (Ag‐MOR) dispersed in polysulfone (PSF), polyimide (PI) or polyetherimide (PEI) were thoroughly analyzed by means of various techniques such as SEM, EDS, XRD, UV‐VIS, FTIR‐ATR, TGA‐SDTA and XPS. Subsequently, the composites were evaluated as antifungal materials for the control of P. roqueforti isolated from contaminated foods of industrial origin. Of all the systems studied, Ag‐MOR/PI demonstrated an outstanding antifungal activity, acting effectively in the control of this mold and reducing the colony growth (CFU mL−1) by a factor of 5 Log after 24 h of contact. This activity was due to highly dispersed cationic silver species immobilized in the film which were effectively dosed towards the microorganism. The Ag‐mordenite/polymer nanocomposite films represent a technological alternative in the search of novel materials for the control of fungal growth. [ABSTRACT FROM AUTHOR]

Milling by a planetary mill was applied as a pretreatment of a reagent mixture for the solvent‐free synthesis of the zeolite mordenite. This method was compared with both manual grinding and standard hydrothermal synthesis. The comprehensive characterization of the obtained products was complemented by thorough studies of activated synthesis mixtures before crystallization steps (by Magic Angle Spinning Nuclear Magnetic Resonance and Scanning Electron Microscopy). This experimental approach gave insight into processes behind the synthesis mixture activation by milling. The characteristics of solvent‐free zeolite product were comparable with material obtained by the classic hydrothermal route. The automated milling activation made the crystallization possible due to higher energetic impact in comparison to manual grinding. The solvent‐free process allowed minimization of the contribution of water to a role of the agent catalyzing silica transformation; as a result, less than 5 % water (compared to the classical synthesis) was necessary to perform the crystallization. [ABSTRACT FROM AUTHOR]

Mordenite (MOR) has demonstrated potential as a catalyst for alkylation due to high variability, intrinsic porosity, and outstanding stability. However, the contact probability of benzene and methanol has been limited by typical layered structures of MOR and there is no connection between layers. Here, we report the preparedness of H‐MOR via a sequential post‐treatment method based on a commercial MOR. H‐MOR sample had appeared lattice imperfections inferred from characterization means. The samples were tested with benezene methylation reaction. Results show that the high conversion of benzene and the high selectivity of toluene were obtained from the miracle role of lattice imperfections in the H‐MOR sample. Sequentially, based on the study of all catalyst structure and physical properties, a plausible reaction mechanism for the selectivity of the desired toluene was proposed. [ABSTRACT FROM AUTHOR]

Copper‐oxo clusters exchanged in zeolite mordenite are active in the stoichiometric conversion of methane to methanol at low temperatures. Here, we show an unprecedented methanol yield per Cu of 0.6, with a 90–95 % selectivity, on a MOR solely containing [Cu3(μ‐O)3]2+ active sites. DFT calculations, spectroscopic characterization and kinetic analysis show that increasing the chemical potential of methane enables the utilization of two μ‐oxo bridge oxygen out of the three available in the tricopper‐oxo cluster structure. Methanol and methoxy groups are stabilized in parallel, leading to methanol desorption in the presence of water. [ABSTRACT FROM AUTHOR]

Conversion of acetylene to C4 olefins enables on‐purpose synthesis of C4 olefins using abundant natural gas resource due to acetylene can be synthesized from methane or ethane. In this study, Cu‐based catalysts supported on SiO2, ZSM‐5 and mordenite (MOR) were tested for acetylene hydrodimerization. Effect of promoters including Ru, Ga, Ag and Pd on the acetylene conversion and C4 olefins selectivity are investigated. The structures of these catalysts were characterized by TEM, XRD, BET, H2‐TPR, NH3‐TPD and XPS measurements. Results showed that temperature, pressure and hydrogen partial pressure had positive effect on acetylene conversion. In the presence of Ru promotor, 100 % acetylene conversion and 87 % selectivity to C4 olefins were achieved over Cu/MOR catalyst under conditions of 0.1 MPa and 200 °C. The mechanistic aspect of acetylene hydrodimerization was elucidated where the C4 intermediate was formed by the reaction between [Cu]−C2H2 π‐complex and [Cu]−C2H2 σ‐complex which were transformed to 1,3‐butadiene and butene. [ABSTRACT FROM AUTHOR]

Propene/propane separation is challenging due to the very small difference in molecular sizes, boiling points and condensabilities between these molecules. Herein, we report a strategy of introducing ZIF fragments into traditional mordenite (MOR) zeolite to decorate the 12‐membered ring of MOR. After decoration, the originally ineffective zeolite MOR exhibited high kinetic propene/propane selectivities (139 at 25 °C) and achieved efficient propene/propane separation. The propene/propane separation potentials of the resulting adsorbents were further confirmed by breakthrough experiments with equimolar propene/propane (50/50) mixtures. [ABSTRACT FROM AUTHOR]

Different post‐synthesis approaches were used to increase the adsorption abilities of zeolite mordenite and Y in removal of cationic dye molecules as typical dyestuff pollutants. Various methods including acid leaching, alkaline treatment, dealumination with hexafluorosilicate, sonication and combination of them were employed to alter the porous structure of various types of selected zeolites. The dealumination (due to acid leaching), desilication (due to alkaline treatment) and disintegration (due to shear forces generated by ultrasound waves) were responsible for the alteration of pores size and accessibility in mordenite. Acid leaching combined with irradiation of ultrasound was found to be most effective technique in adsorption of rhodamine B as a large dye molecule into mordenite. In the case of zeolite Y, a chemical treatment with ammonium hexafluorosilicate resulted in considerable improvement of adsorption of rhodamine B. [ABSTRACT FROM AUTHOR]

Catalytic isobutyl alcohol oligomerization to generate hydrocarbon liquid fuels over zeolite has been investigated over H−Y, SAPO‐34, H‐MOR zeolite and Al‐MCM‐41 catalysts, as a new way to direct conversion of isobutyl alcohol to hydrocarbon liquid fuels, considering the fact that isobutyl alcohol can be obtained from biomass by microbes. In this study, all of the zeolite samples showed good reactivity, especially H‐MOR, achieving 94 % conversion of isobutyl alcohol and 63 % selectivity of C5+ liquid fuels in all products. The effects of reaction conditions including reaction temperature and reaction time were also discussed. The physicochemical properties of the catalysts were characterized by XRD, Nitrogen adsorption‐desorption, NH3‐TPD, TG/DTA, and GS/MS. The reaction system discussed here involves two reactions, i) isobutyl alcohol dehydration reaction via a typical acid catalysis, ii) a polymerization reaction of small molecules into large ones, according to the experimental and characterization results, the pore size and acid property of the zeolite are the two main factors controlling this catalytic dehydration and oligomerization reaction. [ABSTRACT FROM AUTHOR]

Glycerol ketalization with acetone to solketal, an oxygenate fuel additive, was demonstrated over hierarchical zeolites of ZSM5, Beta and Mordenite structure in a continuous flow system. Micro‐mesoporous zeolites were prepared in two steps, by means of alkaline treatment with NaOH followed by the ionic exchange with NH4NO3 and a subsequent treatment with citric acid. The presence of mesopores in the applied catalysts was confirmed by N2 adsorption/desorption measurements and TEM microscopy. Hierarchical zeolites showed superior catalytic performance and lifetime over 24 hours under mild conditions (atmospheric pressure, acetone to glycerol molar ratio of 3 : 1, WHSV of 3–8 h−1, reaction temperature of 323 K). Glycerol conversion of about 90 % and selectivity to solketal up to 98 % have been obtained over micro‐mesoporous catalysts within 24 h without any drop of performance and the symptoms of clogging. Among all hierarchical catalysts tested in a flow reactor, the very high activity defined as solketal yield (88 %) showed ZSM5 and Beta zeolites. [ABSTRACT FROM AUTHOR]

The reaction of methane with copper‐exchanged mordenite with two different Si/Al ratios was studied by means of in situ NMR and infrared spectroscopies. The detection of NMR signals was shown to be possible with high sensitivity and resolution, despite the presence of a considerable number of paramagnetic CuII species. Several types of surface‐bonded compounds were found after reaction, namely molecular methanol, methoxy species, dimethyl ether, mono‐ and bidentate formates, CuI monocarbonyl as well as carbon monoxide and dioxide, which were present in the gas phase. The relative fractions of these species are strongly influenced by the reaction temperature and the structure of the copper sites and is governed by the Si/Al ratio. While methoxy species bonded to Brønsted acid sites, dimethyl ether and bidentate formate species are the main products over copper‐exchange mordenite with a Si/Al ratio of 6; molecular methanol and monodentate formate species were observed mainly over the material with a Si/Al ratio of 46. These observations are important for understanding the methane partial oxidation mechanism and for the rational design of the active materials for this reaction. [ABSTRACT FROM AUTHOR]

Which post‐synthetic modification strategy is the best suited for the generation of particular textural or chemical features in mordenite for a desired catalytic application? The aim of this contribution is to shed light on the effective quality of zeolite hierarchization through the rational study of structure/catalytic property dependency. Our study focused on mordenite, as this zeolite is of particular importance due to its strong acidity and monodimensional channel system, which explains why mordenite is industrially extensively employed. A toolbox of post‐synthetic hierarchization strategies on aluminum rich and poor mordenites has been developed based on basic treatments assisted by CTAB and pyridine at various temperatures (in conventional and microwave heating) and acid HF etching in aqueous and organic medium. A systematic study of over 30 post‐synthetically modified mordenites was conducted, which allowed us to assess the impact of each hierarchization strategy on textural, morphological, chemical and catalytic properties. Major correlations between structural features and catalytic activity, selectivity and stability in both the monomolecular n‐hexane cracking and the bimolecular toluene disproportionation were deduced. [ABSTRACT FROM AUTHOR]

We report the synthesis of hierarchical mordenite zeolite nanorods in one step using inexpensive mono-quaternary ammonium N-cetyl-N-methylpyrrolidinium (C16NMP) as mesoporogen to the synthesis gel. The presence of a small amount of C16NMP results in the formation of 0.6-1 μm rods-like crystals oriented along the c-axis with a high mesoporous volume (0.12 cm³g-1) and external surface area (~90 m²g-1 compared to bulk mordenite. Acidity characterization shows that the presence of C16NMP during mordenite formation leads to a redistribution of aluminum in the zeolite framework: the amount of Brønsted acid sites in the side-pockets (8MR channels) is increased at the expense of those in the 12MR main channels. As these latter acid sites are the ones involved in the conversion of alkene intermediates in bifunctional hydroconversion of alkanes, an optimized hierarchical mordenite prepared with C16NMP displays a more ideal hydrocracking selectivity than bulk MOR prepared solely with sodium. [ABSTRACT FROM AUTHOR]

Zeolite crystals can be used as seeds or aluminosilicate sources in syntheses to control polymorphs and/or reduce the quantity of organics used as structure‐directing agents. A frequently invoked hypothesis for interzeolite transformations is that zeolites share some underlying similarity in structure, most notably in cases pertaining to organic‐free syntheses. Herein, we show for the first time that ZSM‐5 (MFI) can be directly obtained from USY (FAU) through an interzeolite transformation between parent–daughter structures lacking common building units in the absence of a structure‐directing agent and seeds. We show that interzeolite transformation leads to a crystalline product with fewer defects. Our findings also reveal that ZSM‐5 is a metastable intermediate that undergoes further transformation to mordenite (MOR) and quartz. The MFI‐to‐MOR transition is counter to reported trends for which transformations lead to structures with reduced molar volume. Herein, we propose mechanistic arguments that suggest the driving force for interzeolite transformation is more complex than guidelines posited in the literature. [ABSTRACT FROM AUTHOR]

Recent research studies have shown that oleic acid can be isomerized to saturated C18 branched‐chain fatty acids through H+‐Mordenite with modest yields (approximately 80 wt.%). The dimensions of tetraethoxysilane (TEOS) (10.3 Å) and triphenylphosphine (TPP) (11.4 Å) are larger than the H+‐Mordenite zeolite, which has a two‐dimensional 8‐member ring (MR) (2.6 Å × 5.7 Å) and 12‐MR (6.5 Å × 7.0 Å) framework. TEOS and TPP are incapable of entering into the internal channels of zeolite, however, they have the ability to poison the acids on the external surface of the H+‐Mordenite. The acidic sites of the specified pore can be selectively catalyzed but most of the active centers on the external surface are deactivated. In this study, all samples were characterized using X‐ray Diffractometry (XRD), scanning electron microscope (SEM), Brunner–Emmet–Teller (BET) measurements, thermogravimetry (TG), NH3‐TPD, and 1H MAS NMR. 2,4,6‐Trimethylpyridine was used for the characterization of the external acidic sites. With TEOS (1 wt.%) and 0.1 mol L−1 TPP‐modified H+‐Mordenite, the Bronsted acid sites on the external surface were reduced by 92.7% and the dimers were reduced from 16.19 wt.% to as low as 4.14 wt.% with 90.09 wt.% yield of saturated C18 branched‐chain fatty acids. [ABSTRACT FROM AUTHOR]

Abstract: Samples of the zeolite mordenite with different Si/Al ratios were used to synthesize materials with monomeric and oligomeric copper sites that are active in the direct conversion of methane into methanol. A comparison of two reactivation protocols with oxygen (aerobic oxidation) and water (anaerobic oxidation), respectively, revealed that such copper–oxo species possess different reactivity towards methane and water. We show for the first time that oligomeric copper species exhibit high activity under both aerobic and anaerobic activation conditions, whereas monomeric copper sites produce methanol only in aerobic processes. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: In this study three natural Yemeni zeolites (NZ1, NZ2 and NZ3) having major minerals such as clinoptilolite and mordenite, were evaluated as low cost sorbents for the removal and recovery of ammonium ions. RESULTS: The zeolite samples, with pHPZC = 9.1 ± 0.2, 7.9 ± 0.2 and 7.4 ± 0.2 for NZ1, NZ2 and NZ3, respectively, showed high ammonium sorption capacities. At pH 8, for treated waste waters: (i) with low NH4+ levels (from 25 to 100 mgNH4/L); and (ii) for concentrated NH4+ side streams generated from the anaerobic digestion of sewage sludge (from 400 up to 1500 mg L‐1), maximum loading capacities of 27 to 51 mgNH4 g‐1 were measured for the studied zeolites. Measured sorption isotherms, in the concentration range 0.05 to 5 g L‐1, were well described by the Langmuir isotherm. The ammonium sorption kinetics was controlled by particle diffusion and was well described by both the homogeneous diffusion (HPDM) and shell progressive (SPM) models. CONCLUSION: Comparison of the equilibrium data with results for natural and synthetic zeolites demonstrate the higher performance of the studied zeolites providing low residual ammonium values <1 mgNH4 g‐1 and <10 mgNH4 g‐1 when treating both diluted and concentrated‐NH4+ streams, respectively. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Sulfonated polyvinylalcohol-mordenite (SPVA-MOR) membranes for direct methanol fuel cell use were synthesized and characterized. It had earlier been found out that polyvinylalcohol-mordenite (PVA-MOR) membranes, while having excellent methanol permeability and modest proton conductivity values, had inferior direct methanol fuel cell performances than Nafion™. Sulfonating the polyvinylalcohol matrix had been suggested to improve the proton conductivity. In this work, polyvinylalcohol powder was sulfonated by using propane sultone as the sulfonating agent prior to the membrane synthesis. Morphological analyses revealed that the zeolite particles mixed homogeneously within the polymer matrix. Sulfonating the polymer slightly decreased both water and methanol uptakes. Both in PVA-MOR and SPVA-MOR membranes, water uptake turned out to be higher than the methanol uptake. SPVA-MOR membranes were found to have an average proton conductivity of 0.052 S·cm−1 when compared with the 0.036 S·cm−1 of PVA-MOR membranes, while Nafion™ has a proton conductivity of approximately 0.1 S·cm−1. The increase in the proton conductivity upon sulfonation despite the decrease in water uptake was explained by the dominance of the Grotthuss mechanism over the vehicular mechanism for proton conductivity. Fuel cell test results showed that while SPVA-MOR membranes cannot outperform Nafion™, they give higher power output than PVA-MOR membranes, especially at low temperatures and high methanol concentrations. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The adsorption process of iodine, a major volatile radionuclide in the off-gas streams of spent nuclear fuel reprocessing, on hydrogen-reduced silver-exchanged mordenite (Ag0Z) was studied at the micro-scale. The gas-solid mass transfer and reaction involved in the adsorption process were investigated and evaluated with appropriate models. Optimal conditions for reducing the silver-exchanged mordenite (AgZ) in a hydrogen stream were determined. Kinetic and equilibrium data of iodine adsorption on Ag0Z were obtained by performing single-layer adsorption experiments with experimental systems of high precision at 373-473 K over various iodine concentrations. Results indicate approximately 91% to 97% of the iodine adsorption was through the silver-iodine reaction. The effect of temperature on the iodine loading capacity of Ag0Z was discussed. The Shrinking Core model describes the data well, and the primary rate controlling mechanisms were macro-pore diffusion and silver-iodine reaction. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1024-1035, 2017 [ABSTRACT FROM AUTHOR]

Three MFI parent zeolites with different morphological properties by different synthesis method were adopted. Alkaline treatment using sodium hydroxide was introduced to modify the structure of MFI zeolites. After iron exchange, the catalytic performance of both parent and modified MFI zeolites were evaluated in the N2O decomposition. The physicochemical properties were systematically characterized with various technologies, such as N2 adsorption-desorption, ICP, XRD, UV-Vis, 27Al MAS-NMR, TEM. The experiment results prove that the Fe-modified MFI catalysts with alkaline pre-treatment show much better catalytic activity than Fe-exchanged parent MFI catalysts. The curves of catalytic activities could move to low temperature range by 50-100 °C. Furthermore, in the presence of NO, the performance gap between Fe-Seed-M, Fe-Solid-M, and Fe-Com-M three samples is obviously reduced. Amongst, for the Fe-Solid-M sample synthesized by the solvent-free method, 90% N2O conversion could be attained at 500 °C, which shows potential to be applied the real condition. It is believed the hierarchical properties and the removal of amorphous substance is beneficial to the diffusion of ion exchange process. Therefore, the increase of active iron sites contributes to the improvement of catalytic performance. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

In the isopropylation of naphthalene for the production of 2,6-naphthalenedicarboxylate, the monomer of polyethylene naphthalate plastic, a shape-selective mordenite (MOR) zeolite catalyst provides the best selectivity for the desired 2,6-diisopropylnaphthalene. However, the small pore size of the zeolite limits the naphthalene conversion and lowers the stability because of pore-mouth blocking by coke. We discovered that these problems could be mitigated by synthesizing a micro-meso hierarchical pore structure in the MOR zeolite by the recrystallization of MOR with cetyltrimethylammonium bromide as a mesopore-forming surfactant. The recrystallized catalysts allow the facile diffusion of bulky molecules through connected meso- and micropores to and from active catalytic sites located in the small MOR pores. Relative to microporous MOR, the hierarchical MOR catalyst demonstrated a greatly enhanced activity, stability, and coke tolerance, and the intrinsic high shape selectivity of MOR for 2,6-diisopropylnaphthalene was maintained. Mild desilication enlarged the pore volume and formed additional acid sites to increase the activity further. [ABSTRACT FROM AUTHOR]

BACKGROUND: Kinetics of adsorption and desorption associated with diffusion mechanisms is of crucial importance to use zeolites as catalysts. In particular, diffusion of ionic liquids (IL) is of interestwhenusing themas solvent for reactions orpreparing composite IL-Zeolite. This work investigated the kinetics of adsorption/desorption of 1-buthyl-3-methylimidazolium bromide ([BMIM]+Br-) intomordenite (MOR), a channel-like zeolite. RESULTS: The adsorbed IL is characterizedandquantified using infraredspectroscopy (FTIR), thermogravimetrical analysis (TGA) and CHN elemental analysis. The results show rapid adsorption of c. 0.7mol of [BMIM]+Br- per gram of MOR but most of it remains in the pores of the zeolite upon desorption because only 9% is desorbed. CHN and TGA also suggest that adsorption of [BMIM]+Br- into the ammonium form of MOR can follow an ionic exchange mechanism. Experimental results can be fitted to a pseudo-second-order kinetic equation. CONCLUSION: The kinetics and mechanisms of adsorption and desorption of [BMIM]+Br- into MOR have been studied. Adsorption kinetics is relatively quick; but only partial desorption occurs probably due to the strength of the [BMIM]+Br--MOR interaction. The observed differences between the adsorption of [BMIM]+Br- into the different forms of MOR give important information on the interactionmechanisms. [ABSTRACT FROM AUTHOR]

Spatial restrictions around catalytic sites, provided by molecular-sized micropores, are beneficial to reaction selectivity but also inherently limit diffusion. The molecular transport can be enhanced by introducing meso- and macropores. However, the impact of this extraframework porosity on the local nanoscale reactivity is relatively unexplored. Herein we show that the area of enhanced reactivity in hierarchical zeolite, examined with super-resolution fluorescence microscopy, is spatially restricted to narrow zones around meso- and macropores, as observed with focused ion-beam-assisted scanning electron microscopy. This comparison indicates that reagent molecules efficiently reach catalytic active sites only in the micropores surrounding extraframework porosity and that extensive macro-porosity does not warrant optimal reactivity distribution throughout a hierarchical porous zeolite. [ABSTRACT FROM AUTHOR]

The isopropylation of naphthalene with isopropyl alcohol was studied over composites of MOR/SBA-15 in a high-pressure, fixed-bed reactor. The MOR catalyst showed a high 2,6-/2,7-diisopropyl naphthalene (DIPN) ratio of 1.75, but a low naphthalene conversion (54 %) and fast deactivation of the catalyst. The composites of MOR/SBA-15 were prepared by a hydrothermal recrystallization process to obtain hierarchical micro/mesopores. During the process, MOR recrystallized in the mesopores of SBA-15, the structure of which was stabilized by carbon coating formed on the pore walls as a template. The best prepared MOR/SBA-15 catalyst achieved a high conversion of 85 %, high stability, and less coking, while maintaining the high 2,6-/2,7-DIPN ratio (≈1.8). The modified micro/mesopore structure allowed facile diffusion of bulky molecules to and from active catalytic sites located in the small MOR pores as a result of the connection between the two types of pores in the MOR/SBA-15 composite. [ABSTRACT FROM AUTHOR]

Unprecedented insight into the carbonylation of dimethyl ether over Mordenite is provided through the identification of ketene (CH2CO) as a reaction intermediate. The formation of ketene is predicted by detailed DFT calculations and verified experimentally by the observation of doubly deuterated acetic acid (CH2DCOOD), when D2O is introduced in the feed during the carbonylation reaction. [ABSTRACT FROM AUTHOR]

This paper presents the kinetics investigation of liquid phase alkylation of benzene with dodecene using mordenite having Si/Al = 20. The models are developed based on physicochemical characterization of the catalyst and a laboratory scale fixed bed reactor data. The FTIR analysis shows that approximately 90 % of the acidic sites are Brønsted acid type while the remaining 10 % are Lewis acid type. The kinetic experiments are conducted with 6:1 molar ratio of benzene to dodecene at four different temperature levels between 80 to 140 °C. The product analysis shows that the main alkylation product is 2-phenyldodecane. At lower temperature, the concentration of dodecene isomers is significant. On the other hand at higher temperature linear alkylbenzene isomers are the dominating products. The kinetic models are formulated considering simultaneous dodecene isomerization and benzene alkylation. The reaction rate parameters are estimated by fitting of the experimental data implemented in MATLAB. The adequacy of the estimated model parameters are verified by thermodynamic consistency and statistical fitting indicators. The activation energy for protonation of 1-dodecene to 2-dodecene found to be significantly lower (34 kJ/mol) than that of the 2-dodecene to 3-dodecene reaction (51 kJ/mol). The activation energies of surface alkylations of benzene to 2-phenyldodecane and 3-phenyldodecane are 49 kJ/mol and 66 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

A novel structured catalyst of binderless micro-HZSM-5 zeolite coating was prepared on stainless-steeled tubes (i.d. 2 mm) through wash coating and vapor-phase transport (VPT) crystallization method. The subsequent crystallization of amorphous SiO2 binders improved the coatings adhesion tremendously by more than 10 times with the least amount of binders (<20% by weight), attributed to the remarkably enhanced interlock by the formed Mordenite Framework Inverted structure between zeolite particles. Catalytic cracking of supercritical n-dodecane (500°C, 4 MPa) was used to examine the catalytic performance of the coatings as prepared, indicating that MZC-V0.2 exhibited a catalytic activity improvement by 8% and a decreased deactivation rate by 48%. The improved catalytic performance may result from its high acid sites amount by incorporating extra-framework Al into HZSM-5 framework, and the possible depressing of pore-mouth deactivation through partial modification of surface acid sites during VPT treatment. This work provides a potential technique to prepare mechanically stable zeolite coatings with high catalytic activity but less binder usage. [ABSTRACT FROM AUTHOR]

BACKGROUND The large Itaya zeolite deposit in Yonezawa, Japan produces good quality, natural zeolite. Its properties as an adsorbent and a functional carrier were assessed and the ion exchange characteristics examined. Natural zeolite has a useful high cation exchange capacity, but has a disadvantage in scattering of the powder. In this study a nonwoven fabric containing zeolite was tested for the removal of cesium. RESULTS The X-ray diffraction ( XRD) peak pattern confirmed that Itaya zeolite is mainly clinoptilolite and contains some mordenite. Ion exchange selectivity of the natural zeolite was Ag+ > Pb2+ > Cu2+ > Zn2+ > Cd2+ > Cr3+ > Ni2+ with almost 100% removal of Ag+ and Pb2+ ions. The cation exchange capacity ( CEC) of Itaya zeolite was 131 cmol kg-1. Low concentrations of Cs+ were removed effectively from the solution with natural zeolite. Cesium ions were removed by ion exchange with potassium and sodium. Cs+ was desorbed from the zeolite with ammonium salt solutions. Elution of Cs+ was influenced by the coordination ability of counter anions. CONCLUSION Satisfactory results were obtained using zeolite-containing nonwoven fabric for the removal of cesium ions. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

In a previous work (Courthial et al.) a transient state characterization method for zeolite supported membranes has been proposed and tested for single components in the Henry domain. An extension of the method to single components beyond the Henry domain and to binary mixtures is described. Since the method is based on experiments performed within the linear domain, the dynamic model previously developed for single components in the Henry domain is extended. The parameter estimation procedure that is described is based on a deep analysis of the model structure with respect to its structural identifiability properties. Some experimental results concerning pure n-butane as well as isobutane/ n-butane mixtures transport through mordenite framework inverted (MFI)-supported membranes are finally shown to illustrate the technique. © 2012 American Institute of Chemical Engineers AIChE J, 59: 959-970, 2013 [ABSTRACT FROM AUTHOR]

The interaction of a single ethanol with pure‐silica and acid mordenite (MOR) has been investigated using density functional theory. Different interaction modes have been studied for three acid sites. All initial structures have been optimized by minimizing the total energy with respect to all lattice parameters and to the atomic coordinates. The nature of the ethanol–acid site complex has been discussed in detail. The strength of the adsorption is directly correlated to the local structural distortion of the MOR framework, especially of the acid site. By using partial density of states method, a detail in the distribution of density of states (orbital) has been obtained. An analysis of the differential charges has been performed, indicating substantial polarization effects for the acid site and for the ethanol molecule as well. Finally, the red‐shift of the harmonic OH stretching frequencies due to the interaction has been estimated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

A micro/mesoporous composite was prepared by a hydrothermal reaction using mordenite and slaked lime to create a comfortable and safe indoor environment. After the hydrothermal reaction, calcium silicate hydrates formed due to the reaction of slaked lime, mordenite, and quartz, led to the generation of mesopores with a broad pore size distribution of more than 3 nm.In this experiment, the microporous structure of mordenite partially collapsed due to dissolution. As compared with mordenite, the composites exhibited higher water-vapor adsorption/desorption properties using their mesopores. The amount of adsorbed harmful gases at 70% relative humidity was larger for the composites than for mordenite. [ABSTRACT FROM AUTHOR]

Spent nuclear fuel contains 129I, which is of particular concern due to its very long half-life, its potential mobility in the environment, and its deleterious effect on human health. In spent fuel reprocessing schemes under consideration, a gas stream containing 129I2 would be passed through a bed of Ag-loaded zeolites such as Ag-mordenite (Ag-MOR). We have investigated the use of a low-temperature sintering bismuth-silicon-zinc-oxide glass powder mixed with either AgI or AgI-MOR to produce dense glass composite material waste forms that can be processed at 550°C, where AgI volatility is low. We have demonstrated that when fine silver flake is added to the mixture, any adsorbed I2 released during heating of AgI-MOR reacts with the silver to form AgI in situ. Furthermore, we have shown that mixtures of the glass with the AgI-MOR or AgI are durable in aqueous environments. Finally, we have developed a process to fabricate core/shell waste forms where the core of AgI-MOR or AgI and glass is encased in a shell of glass that protects the core from contact with the environment. To prevent cracking of the shell due to thermal expansion mismatch between the core and shell, amorphous silica was added to the shell to form a composite with a lower coefficient of thermal expansion. [ABSTRACT FROM AUTHOR]

This study compared the adsorption behavior of Na+ and Ni2+ by zeolite minerals that differed only in the physical size of the nanopores in their interstitial regions. Any differences observed in the adsorption of these ions were interpreted in terms of how the physical variations of their nanopores might be involved. The adsorption strength of Ni2+ was weak with zeolite Y and ZSM-5 but strong with mordenite. The adsorption strength of Na+ was weak with zeolite Y but strong with ZSM-5 and mordenite. Even when Na+ adsorbed weakly, its adsorption strength was comparable to that of Ni2+ Similarly, when both adsorbed strongly, they both adsorbed with nearly the same strength. The adsorption reaction is a three-way competition between H+, Na+, and Ni2+ for the adsorption sites. We propose a new theory to explain the increase in adsorption by the ZSM-5 zeolite for Na+ and by mordenite for Na+ and Ni2+ The new theory states that a dehydrated inner sphere adsorbing ion will be stable if either the ion's attraction to the surface site is stronger than toward the bulk water or the ion's attraction to the bulk water is offset by hindering the presence of water in the region. This occurs when the nanopore diameters are larger than the ionic diameter of the ion but much smaller than the hydrated diameter of the ion, which occurs with interstitial cavities that are not greater than approximately 0.3 to 0.5 nm in size in at least one dimension. [ABSTRACT FROM AUTHOR]

A new series of calcium oxide clusters Ca2OX (X = 1–4) at cationic positions of mordenite (MOR) and faujasite (FAU) is studied via the isolated cluster approach. Active oxide framework fragments are represented via 8-membered window (8R) in MOR, and two 6R and 4R windows (6R+4R) possessing one common Si&bond;O&bond;Si moiety in FAU. Structural similarities between the Ca2OX(8R) and Ca2OX(6R+4R) moieties are considered up to X = 4. High oxidation possibilities of the Ca2O2(nR) and Ca2O3(nR) systems are demonstrated relative to CO, whose oxidation over the Ca-exchanged zeolite forms is well studied experimentally. Relevance of the oxide cluster models with respect to trapping and desorption of singlet dioxygen is discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [ABSTRACT FROM AUTHOR]

Front Cover: Importance of Methane Chemical Potential for Its Conversion to Methanol on Cu-Exchanged Mordenite (Chem. Eur. J. 34/2020) Keywords: chemical potential; copper-trimer; methane oxidation; methanol production; zeolite EN chemical potential copper-trimer methane oxidation methanol production zeolite 7511 7511 1 06/22/20 20200618 NES 200618 B Tricopper-oxo clusters [Cu SB 3 sb ( -O) SB 3 sb ] SP 2+ sp b hosted in mordenite can selectively oxidize methane to methanol but yields are limited. Chemical potential, copper-trimer, methane oxidation, methanol production, zeolite. [Extracted from the article]