Ion-exchanged Zeolite Research Articles

Modification of commercial NaY zeolite to give high water diffusivity and adsorb a large amount of water

By using NaY zeolites as desiccant materials, commercial NaY zeolite was alkali treated with 1M NaOH aqueous solution and then Mg2+ ion-exchanged by 0.5M Mg(NO3)2 aqueous solution. Alkali treatment (AT) of NaY zeolite removed silicon atoms selectivity from the framework of Y-type zeolite and enhanced water diffusivity of Y-type zeolite. On the other hand, Mg2+ ion-exchange of NaY zeolite increased the amount of water adsorbed. Prepared Y-AT-Mg zeolite had both water adsorption velocity and a large difference of water adsorbed amount between adsorption at 30°C and desorption at 100°C.

Mechanical performance and CO2 uptake of ion-exchanged zeolite A structured by freeze-casting

Zeolite 4A has been freeze-cast into highly porous monoliths with a cylindrical shape. The brittle monoliths, with lamellar or columnar pores and wall thicknesses between 8 and 35μm, show a compressive mechanical response along the main pore axis that could be modeled by a buckling behavior. The failure strength is proportional to the density and the amount of transverse bridging across lamella, which was shown to be related to the pore cross-sectional aspect ratio. Monoliths with highly anisotropic pores with a cross-sectional aspect ratio higher than 3 yielded sequentially from the top surface, whereas monoliths with a pore aspect ratio lower than 3 were found to delaminate into longitudinal splinters. The freeze-cast monoliths show a sharp gas breakthrough front with a 1:9 mixture of CO2 and N2, indicating rapid uptake kinetics of the lamellar structures.

Fabrication of Nanocatalyst in Aqueous Solution With Photocatalytic Activity of Methylene Blue

Nanocomposites of PbS and MCM-41 nanoparticles were prepared via an ion exchange route. The samples were obtained by sulfidation of the Pb2+ ion-exchange zeolite in a Na2S solution at room temperature. The catalyst is characterized by transmission electron microscopy, X-ray diffraction, and infrared spectroscopy. The effect of PbS, MCM-41 support and different wt% of PbS over the support on the photocatalytic degradation and influence of parameters such as PbS loading, catalyst a mount, pH, and initial concentration of dye on degradation are evaluated. The prepared catalysts exhibit high efficient photocatalytic activity on degrading methylene blue under UV irradiation.

Selective oxidation of cyclooctene over copper-containing metal-organic frameworks

The selective oxidation of cyclooctene with tert-butylhydroperoxide (TBHP) was studied over Cu-containing MOFs at 348 K in liquid toluene. With Cu3(BTC)2, complete conversion was achieved after 120 h. The epoxide selectivity steadily increases to >80%. The conversion is accelerated by a radical initiator and decelerated by a radical inhibitor. A radical-based mechanism is proposed with alkoxy- or polyperoxides being formed as intermediates to the epoxide. The comparison of the cyclooctene conversion with TBHP over Cu3(BTC)2 with FeBTC, the ion-exchanged zeolites Na,Cu-Y and Na,Fe-Y and TS-1 proves that Cu3(BTC)2 is active for radicals generation from TBHP, but less suitable for catalyzing alkene epoxidation. The two recently reported Cu-MOFs [Cu(Me-4py-trz-ia)]∞3 and [(Cu4(μ4-O)(μ2-OH)2(Me2trz-pba)4]∞3 are up to four times more active for cyclooctene oxidation than Cu3(BTC)2. This was attributed to the specific coordination geometry of the catalytically active Cu sites within these materials. Moreover, the liquid-phase conversion of cyclooctene with TBHP is shown to be a sensitive test reaction to evaluate the potential of new solid oxidation catalysts, especially of transition metal-containing MOFs.

Direct observation and structural characterization of natural and metal ion-exchanged HEU-type zeolites

The atomic structure of natural HEU-type zeolite and two ion-exchanged variants of the zeolite, Ag+ (Ag-HEU) and Zn2+ (Zn-HEU) ion exchanged HEU-type zeolites, are investigated using advanced transmission electron microscopy techniques in combination with X-ray powder diffraction and X-ray absorption fine structure measurements. In both ion-exchanged materials, loading of the natural HEU zeolite is confirmed.Using low-voltage, aberration-corrected transmission electron microscopy at low-dose conditions, the local crystal structure of natural HEU-type zeolite is determined and the interaction of the ion-exchanged natural zeolites with the Ag+ and Zn2+ ions is studied. In the case of Ag-HEU, the presence of Ag+ ions and clusters at extra-framework sites as well as Ag nanoparticles has been confirmed. The Ag nanoparticles are preferentially positioned at the zeolite surface. For Zn-HEU, no large Zn(O) nanoparticles are present, instead, the HEU channels are evidenced to be decorated by small Zn(O) clusters.

Design and Synthesis Functional Selective Catalytic Reduction Catalyst for NOx Removal

MeOx-Cu-SSZ-13 (Me=Mn, Ce) was synthesized by physically mixing mental oxide and ion-exchanged zeolite. The composite catalyst showed highly efficient for the NOx removal using NH3-SCR method. And the NO conversion is 98% for MnOx-CeO2/Cu-SSZ-13 at 150°C and 97% for MnOx/Cu-SSZ-13 at 175°C. Meanwhile, the N2 selectivity remains more than 98%. The catalysts are characterized by using XRD and SEM. The XRD patterns show that all samples are highly crystallized and without impurities. The SEM demonstrates all samples have uniform crystal size. Composite catalyst especially combined with Cu-SSZ-13 has considerable potential as a catalyst in the area of NOx conversion.

Metal ion-exchanged zeolites as highly active solid acid catalysts for the green synthesis of glycerol carbonate from glycerol

The application of metal ion-exchanged zeolites as highly efficient catalysts for the synthesis of glycerol carbonate from glycerol carbonylation is reported.

CO2 Sequestration by Natural Zeolite for Greenhouse Effect Control

This paper describes the adsorption of CO2 on pores in natural erionite exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, variable time and temperature of treatment. Experimental data of CO2 adsorption were treated by the Freundlich and Langmuir equations. Complementarily were evaluated standard adsorption energies and the degree of interaction of the gas with the zeolite; the evolution of isosteric heats of adsorption was analyzed. The exchange with Na+ favors the creation of emergent pores thus causing an increase of the adsorption capacity for CO2. The presence of Na+ at micropore entrances causes an increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. The development of nanopores in erionite was evaluated through the Barrett-Joyner-Halenda and NLDFT methods. Depending on the conditions of the exchange treatment, Na+ was found to be most favorable, well distributed, and accessible for N2 adsorption.

B213 シビアアクシデント対策としての放射性ヨウ素吸着剤Agxの応用について(OS3 軽水炉・新型炉・原子力安全(3))

Since the Fukushima nuclear accident in 2011, nuclear power plants in Japan have taken or are taking the safety countermeasures which are considered on the premise that an accident may occur. These countermeasures include installing and improving the filter vents for preventing contamination of radioiodine. For this reason, silver ion-exchanged zeolite (Rasa-AgX) as a radioiodine adsorbent has been developed and its adsorption characteristics of radioiodine have been investigated. The evaluation results show that Rasa-AgX has the very high adsorption efficiencies even if under the harsh conditions such as high temperature, high humidity and high pressure. In particular, it can still keep the good adsorption performances in the atmosphere of water condensation and at the low DPDs (Dew Point Distances) of zero and 2 K. Owing to these excellent performances, Rasa-AgX is being utilized in filter vent system to capture radioiodine, and it is expected to be applied to more nuclear power plants, reprocessing plants and other nuclear facilities.

Ion exchange of zeolite membranes by a vacuum ‘flow-through’ technique

Ion exchange of nanoporous (e.g., zeolite) membranes is of increasing importance in their applications as separation devices and catalytic reactors. Ion exchange processes in zeolite membranes are significantly limited by slow hydrated-ion transport rates and the low liquid–solid interfacial area available in comparison to ion exchange of zeolites in powdered form, thereby leading to long membrane processing and regeneration times. Here, we consider ion exchange processes in zeolite membranes in more detail, and show the much higher efficacy of a vacuum-assisted liquid–vapor ‘flow-through’ method in comparison to both the conventional ‘immersion/counter-diffusion’ method as well as a liquid–liquid flow-through method. Na-MFI zeolite disk membranes, made by both in situ and seeded growth, were ion-exchanged with Ga3+, Zn2+, and Pt2+ ions in the temperature range of 23–70°C and exchange times of 5–24h. The penetration of these ions into the zeolite membranes was investigated in detail by energy-dispersive X-ray (EDX) spectroscopy. Surprisingly, the quantity of exchanged ions in the membranes via the vacuum-assisted ‘flow-through’ technique is found to exceed that achieved by the other two methods by up to a factor of ten, with the liquid–liquid technique being the least efficient. Higher temperatures and longer ion exchange times increased the ion exchange efficiency in the vacuum-assisted method. Chemical analysis of the condensed permeate solution by inductively-coupled plasma (ICP) mass spectrometry revealed that both the original Na+ and replacement metal cations moved through the membrane in a co-current manner, unlike the conventional counter-current movement of ions in the immersion process. The Na+ ions in the membrane experience pressure-driven transport (along with water molecules) to the permeate side, and leave the membrane surface as hydrated vapor-phase cations, thereby allowing the maintenance of a high driving force for ion exchange. In contrast, the conventional counter-current flow technique leads to a decreasing concentration driving force with time. The liquid–liquid method, even though having the same ion concentration and applied pressure driving force as the liquid–vapor method, is very slow because of the large osmotic gradient opposing the permeation of ions and water from the feed to the permeate side. The liquid–vapor ion exchanged MFI membranes showed excellent integrity (as determined by H2 and CO2 permeation measurements).

Catalysts for NOx selective catalytic reduction by hydrocarbons (HC-SCR)

This short review concerns the efficient catalysts for HC-SCR discovered more than 20 years ago. In 1990, Iwamoto proposed Cu ion-exchanged ZSM-5, and it was the first powerful catalyst for HC-SCR. This paper presents first metal ion-exchanged zeolites and the influence of various parameters on the catalysts activities (acidity, O2 content, etc.). In the second part, this paper reviews supported metal catalysts, base metal oxides, hybrid catalysts and the possible reducing agents to remove NOx. It can be inferred that the most active catalysts for HC-SCR should have acidic sites, an active phase like copper or cobalt, or for a wider activity, elements such as silver or a mixture of metals. For low deactivation, they should contain noble metals such as platinum, rhodium or tin.

Coordination Environment of Copper Sites in Cu-CHA Zeolite Investigated by Electron Paramagnetic Resonance

Cu-CHA combines high activity for the selective catalytic reduction (SCR) reaction with better hydrothermal stability and selectivity compared to other copper-substituted zeolites. At the same time Cu-CHA offers an opportunity for unraveling the coordination environment of the copper centers since the zeolite framework is very simple with only one crystallographically independent tetrahedral site (T-site). In this study the results of an X-band electron paramagnetic resonance (EPR) investigation of ion-exchanged Cu-CHA zeolite with a Si/Al ratio of 14 ± 1 is presented. Different dehydration treatments and rehydration experiments are performed in situ while monitoring with EPR. The results are compared with recent literature evidence from temperature-programmed reduction, X-ray methods, IR spectroscopic methods, and UV–visible spectroscopy. On the basis of these findings quantitative information is obtained for the different copper positions in dehydrated Cu-CHA. The well-defined copper sites in the six-me...

Zeolite Y adsorbents with high vapor uptake capacity and robust cycling stability for potential applications in advanced adsorption heat pumps

Modular and compact adsorption heat pumps (AHPs) promise an energy-efficient alternative to conventional vapor compression based heating, ventilation and air conditioning systems. A key element in the advancement of AHPs is the development of adsorbents with high uptake capacity, fast intracrystalline diffusivity and durable hydrothermal stability. Herein, the ion exchange of NaY zeolites with ingoing Mg2+ ions is systematically studied to maximize the ion exchange degree (IED) for improved sorption performance. It is found that beyond an ion exchange threshold of 64.1%, deeper ion exchange does not benefit water uptake capacity or characteristic adsorption energy, but does enhance the vapor diffusivity. In addition to using water as an adsorbate, the uptake properties of Mg, Na-Y zeolites were investigated using 20wt.% MeOH aqueous solution as a novel anti-freeze adsorbate, revealing that the MeOH additive has an insignificant influence on the overall sorption performance. We also demonstrated that the lab-scale synthetic scalability is robust, and that the tailored zeolites scarcely suffer from hydrothermal stability even after successive 108-fold adsorption/desorption cycles. The samples were analyzed using N2 sorption, 27Al/29Si MAS NMR spectroscopy, ICP-AES, dynamic vapor sorption, SEM, Fick’s 2nd law and D–R equation regressions. Among these, close examination of sorption isotherms for H2O and N2 adsorbates allows us to decouple and extract some insightful information underlying the complex water uptake phenomena. This work shows the promising performance of our modified zeolites that can be integrated into various AHP designs for buildings, electronics, and transportation applications.

Theoretical investigation of novel two-step decomposition of nitric oxide over Fe(II) ion-exchanged zeolites using DFT calculations

A new method for the direct catalytic decomposition of nitric oxide (NO) is proposed in order to overcome several well-known problems toward its practical use. In this novel methodology, NO is first selectively adsorbed on Fe(II) ion-exchanged zeolites (LTA, MFI, and FAU) in the presence of excess oxygen; the concentrated NO in the zeolite microchannels is then decomposed by low-energy irradiation. The NO molecule is selectively adsorbed on Fe(II)–zeolites under the excess oxygen conditions, and that NO bond cleavage is more likely to occur for NO on Fe(II) than in the gas phase, because Fe(II) supplies an electron into an orbital of the NO molecule. A dinitrosyl species formed on Fe(II) sites in zeolites is decomposed via a N2O intermediate with lower activation energy. Achieving a closer distance between the two nitrogen atoms of two NO molecules by concentrating them on Fe(II) in zeolitic microcages is key to accelerate the decomposition with greatly reduced energy requirements. Based on these results, a catalytic redox cycle of Fe(II) in zeolites for NO decomposition is proposed, where the largest activation energy (the rate-determining step) is for the reaction 2NO→N2O+O (ca. 160kJ/mol), which is higher than that of NO decomposition on Cu-ZSM-5 (ca. 135kJ/mol). It is proposed that imitating the molecular mechanism of fungal nitric oxide reductase (P450nor) by utilizing an adjacent proton on Fe(II) ion-exchanged proton-form zeolite, the required energy for 2NO→N2O+O decreases further (ca. 40kJ/mol), allowing for successful reaction initiation with low-energy irradiation such as microwaves.

LTA and ion-exchanged LTA zeolite membranes for dehydration of natural gas

This work presents synthesis and characterization of LTA-type zeolite membranes on α-Al2O3 substrate via secondary growth method. The membranes were prepared with the aim of applying for dehydration of natural gas. Zeolite NaA membranes were synthesized using hydrothermal method and the pore size of the membranes was then adjusted to 3Å by ion exchanging the zeolite layer. Potassium chloride (KCl) aqueous solution was utilized as the ion-exchange reagent. The molarity of KCl solution varied from 0.1 to 1M to figure out the best conditions for the synthesis of KA zeolite membranes. The synthesized membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Energy-dispersive X-ray spectroscopy (EDX). Separation performance of synthesized membranes was evaluated via permeation of water vapor and methane, as a model of natural gas. The results showed that by increasing molarity of KCl solution from 0.1 to 1M, the permeation of CH4 was reduced. The membranes ion-exchanged in KCl solution with molarity of 0.6M was chosen as the optimum condition.

Ruthenium(III) ion-exchanged zeolite Y as highly active and reusable catalyst in decomposition of nitrous oxide to sole nitrogen and oxygen

Ruthenium(III) ion-exchanged zeolite Y, prepared by ion exchange of Ru+3 ions with the extra framework Na+ cations in zeolite Y with a Si/Al ratio of 2.5, is employed to catalyze the decomposition of nitrous oxide to nitrogen and oxygen. Catalytic activity of ruthenium(III) ion-exchanged zeolite Y is studied in the decomposition of nitrous oxide to nitrogen and oxygen depending on the ruthenium loading of zeolite and flow rate of nitrous oxide helium mixture in a continuous flow vertical reactor. The results collected reveal that ruthenium(III) ion-exchange zeolite with a ruthenium loading of 3.98wt.% is highly active, long-lived, and reusable catalyst providing 100% conversion of nitrous oxide to sole nitrogen and oxygen at 350°C without any side reaction. This catalyst can be bottled under ambient conditions and repeatedly used in successive runs of nitrous oxide decomposition for up to 5months without significant loss in activity. Intrazeolite ruthenium(0) nanoclusters are slightly less active than the ruthenium(III) ion-exchanged zeolite Y in decomposition of nitrous oxide, which might be attributed to the migration of ruthenium(0) to the external surface before oxidation at high temperature. The other two metals of Group 8, iron(III) and osmium(III) ion-exchanged zeolite Y do not show activity as high as that of ruthenium(III) ion-exchanged zeolite Y in the same reaction.

Dimethyl Ether Synthesis via Methanol Dehydration over BEA Zeolite from Bagasse Fly Ash with Zircronium- and Nickel-Ion Exchange

The synthesis of dimethyl ether via methanol dehydration has been carried out over Beta zeolite (BEA) and ion-exchanged Beta zeolite from bagasse fly ash using hydrothermal method. The reactions were taken place in a fixed-bed reactor. The effects of nickel and zirconium ion-exchanged of BEA were investigated. Ni-BEA zeolite exhibited high methanol conversion rate and DME-resultant upon the reaction temperature from 200 to 225°C with equilibrium-limiting condition over 225°C; Furthermore, the Ni-BEA zeolite presented the best stable activity at 225°C over 1,200 minute. The Ni-BEA zeolite has also been interesting as a zeolite which suited to be one role importance to improve the properties for methanol dehydration to dimethyl ether.

Desulfurization Performance of Cu(II)-Ce(IV)/13X Zeolites for C<sub>4</sub> Hydrocarbon

Basic research of adsorptive desulfurization was carried out concerning the high total sulfur concentration of C4hydrocarbon which was the reason for exceeding total sulfur concentration of MTBE. Based on the screening of active components, Cu (II)-Ce (IV) bimetal ion-exchanged 13X zeolites were prepared. Desulfurization performance of 13X zeolites modified with different metals was investigated by using model C4hydrocarbon which contained dimethyl disulfide (DMDS), dimethyl sulfide (DMS), and tert-butyl mercaptan (TBM). The Cu (II)-Ce (IV)/13X zeolites exhibited better desulfurization performance for C4hydrocarbon due to the formation of sulfur-metal (S-M) bond between metal and sulfur compounds.

Highly efficient catalytic oxidation of cyclohexanol with TBHP over Cr-13X catalysts in a solvent-free system

With respect to the consideration of environment and economy, simple, inexpensive, and reusable solid catalysts have been attracting much attention. In this work, a series of non-noble transition-metal ion-exchanged zeolite catalysts have been prepared and applied in the catalytic oxidation of cyclohexanol and other alcohols with tert-butyl hydroperoxide (TBHP) to aldehydes or ketones in the absence of any solvent and additive. Among various catalysts tested, Cr3+-exchanged 13X has exhibited the best activity with the highest efficiency of TBHP utilization, and been proven to be a recyclable heterogeneous catalyst for the oxidation of cyclohexanol with TBHP. The effects of the Cr loading, the reaction temperature, the reaction time, and the cyclohexanol/TBHP molar ratio have been investigated systematically. Furthermore, a feasible oxidation route is proposed.

Monte Carlo simulation studies of cation selectivity in ion exchange of zeolites

The ion-exchange isotherms for various zeolites are investigated by Monte Carlo simulation to numerically evaluate their cation selectivity.0