Ion-exchanged Zeolite Research Articles

Impact of Thermal and Chemical Ageing of Fe-BEA SCR Catalyst on NOx Conversion Performance

Emissions of nitrogen oxides (NOx) from heavy-duty diesel engines are subject to more stringent environmental legislation. Selective catalytic reduction (SCR) over metal ion-exchanged zeolites is in this connection an efficient method to reduce NOx. Understanding durability of the SCR catalyst is crucial for correct design of the aftertreatment system. In the present paper, thermal and chemical ageing of Fe-BEA as NH3-SCR catalyst is studied. Experimental results of hydrothermal ageing, and chemical ageing due to phosphorous and potassium exposure are presented. The catalyst is characterized by flow reactor experiments, nitrogen physisorption, DRIFTS, XRD, and XPS. Based on the experimental results, a multisite kinetic model is developed to describe the activity of the fresh Fe-BEA catalyst. Furthermore, the model can predict deactivation of the catalyst well by decreasing the number of active sites, representing loss of active iron sites due to migration or chemical blockage of the sites. By performing a systematic study of different deactivation mechanisms, a deactivation expression for the active sites can be formulated.

Material Exhibiting Efficient CO2 Adsorption at Room Temperature for Concentrations Lower Than 1000 ppm: Elucidation of the State of Barium Ion Exchanged in an MFI-Type Zeolite.

Carbon dioxide (CO2) gas is well-known as a greenhouse gas that leads to global warming. Many efforts have been made to capture CO2 from coal-fired power plants, as well as to reduce the amounts of excess CO2 in the atmosphere to around 400 ppm. However, this is not a simple task, particularly in the lower pressure region than 1000 ppm. This is because the CO2 molecule is chemically stable and has a relatively low reactivity. In the present study, the CO2 adsorption at room temperature on MFI-type zeolites exchanged with alkaline-earth-metal ions, with focus on CO2 concentrations <1000 ppm, was investigated both experimentally and by calculation. These materials exhibited a particularly efficient adsorption capability for CO2, compared with other presented samples, such as the sodium-form and transition-metal ion-exchanged MFI-type zeolites. Ethyne (C2H2) was used as a probe molecule. Analyses were carried out with IR spectroscopy and X-ray absorption, and provided significant information regarding the presence of the M(2+)-O(2-)-M(2+) (M(2+): alkaline-earth-metal ion) species formed in the samples. It was subsequently determined that this species acts as a highly efficient site for CO2 adsorption at room temperature under very low pressure, compared to a single M(2+) species. A further advantage is that this material can be easily regenerated by a treatment, e.g., through the application of the temperature swing adsorption process, at relatively low temperatures (300-473 K).

Effects of Si/Al Ratio on Adsorptive Removal of Thiophene and Benzothiophene over Ion-Exchanged AgCeY Zeolites

AgCeY-n zeolites with different Si/Al ratios n (n = 3.0, 4.8, and 5.3) were successfully prepared and characterized by XRD, BET analysis, SEM, IR spectroscopy, XPS, FTIR spectroscopy, and ICP analysis. The effects of the Si/Al ratio on the adsorptive desulfurization properties of the adsorbents were evaluated. The results showed that AgCeY-5.3 exhibited the best sulfur removal capacity and selectivity. The capacity for sulfur removal onto AgCeY-n decreased in the order AgCeY-5.3 > AgCeY-4.8 > AgCeY-3.0 for a model oil comprising thiophene (TP) and benzothiophene (BT), along with certain amounts of toluene or cyclohexene. The adsorption affinity of the sulfur compounds was in the order BT > TP. In addition, the inhibition effects on the AgCeY-n zeolites for sulfur removal were in the order cyclohexene > toluene. The removal of organic sulfur compounds onto AgCeY-n was mainly by π-electronic and direct coordination (S–M) interaction.

Low-pressure performance evaluation of CO2, H2O and CH4 on Li-LSX as a superior adsorbent for air prepurification

High-volume production of oxygen and nitrogen from atmospheric air is accomplished by cryogenic distillation. Prior to feeding to the air separation unit, the ambient air must be pre-purified by the removal of trace impurities such as CO2, H2O vapor, and light hydrocarbons (e.g., CH4) to their tolerable limits of 1.0ppm, 0.1ppm, and to a few ppb, respectively. In this study, the adsorption characteristics of a synthetic zeolite, Li-LSX (where LSX denotes low-silica type-X zeolite where Si/Al=1), for the removal of trace amounts of CO2, CH4, and H2O vapor impurities were analyzed and compared with the conventional synthetic 13X zeolite that has been used for air prepurification as well as the ion-exchanged K-LSX and Ca-LSX zeolites. Isotherms to very low partial pressures (to a few ppm of 1atm) were measured. The Tὸth, Langmuir–Freundlich (L–F), and the Dubinin–Astakhov (D–A) isotherm models were used to correlate the low pressure experimental data and the Tὸth model was found to be the better fit especially in the low pressure range. The superior adsorption properties of Li-LSX for air prepurification are demonstrated in this work.

Preparation and characterization of Ag+ ion-exchanged zeolite-Matrimid®5218 mixed matrix membrane for CO2/CH4 separation

In this work, the zeolite-Y was ion-exchanged by introducing silver cations into the framework of micro-sized nano-porous sodium zeolite-Y using a liquid-phase ion exchanged method. The Ag+ ion-exchanged zeolite, was then embedded into the Matrimid®5218 matrix to form novel mixed matrix membranes (MMMs). The particles and MMMs were characterized by ultraviolet-visible diffuse reflectance spectroscopy (UV–vis DRS), N2 adsorption–desorption isotherm, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Furthermore, the effects of filler content (0–20 wt%) on pure and mixed gas experiments, feed pressure (2–20bar) and operating temperature (35–75ºC) on CO2/CH4 transport properties of Matrimid/AgY MMMs were considered. Characterization results confirmed an appropriate ion-exchange treatment of the zeolites. The SEM results confirmed the superior interfacial adhesion between polymer and zeolites, particularly in the case of Matrimid/AgY membranes. This is due to the proper silverous zeolite/Matrimid functional groups’ interactions. The gas permeation results showed that the CO2 permeability increased about 123%, from 8.34 Barrer for pure Matrimid to 18.62 Barrer for Matrimid/AgY (15 wt%). The CO2/CH4 selectivity was improved about 66%, from 36.3 for Matrimid to 60.1 for Matrimid/AgY (15 wt%). The privileged gas separation performance of Matrimid/AgY (15 wt%) was the result of a combined effect of facilitated transport mechanism of Ag+ ions as well as the intrinsic surface diffusion mechanism of Y-type zeolite. In order to survey the possibility of using the developed MMMs in industry, the CO2-induced plasticization effect and mixed gas experiment were accomplished. It was deduced that the fabricated MMMs could maintain the superior performance in actual operating conditions.

Smart epoxy coating containing Ce-MCM-22 zeolites for corrosion protection of Mg-Li alloy

The epoxy coatings containing MCM-22 and Ce-MCM-22 zeolites were prepared by coating method on the Mg-Li alloy surface. The influence of MCM-22 and Ce-MCM-22 zeolites on corrosion protection of the epoxy coating was studied. The epoxy coating containing Ce-MCM-22 zeolites showed high corrosion resistance. Artificial defects in the epoxy coating containing Ce-MCM-22 zeolites on the Mg-Li surface were produced by the needle punching. The results show that the epoxy coating containing Ce-MCM-22 zeolites exhibits self-healing corrosion inhibition capabilities. It is ascribed to the fact that the Ce3+ ions are released from MCM-22 zeolites based on ion exchange of zeolite in the corrosion process of the Mg-Li alloy substrate. MCM-22 zeolites as reservoirs provided a prolonged release of cerium ions.

Antimicrobial Activity of Silver Ions Released from Zeolites Immobilized on Cellulose Nanofiber Mats.

In this study, we exploit the high silver ion exchange capability of Linde Type A (LTA) zeolites and present, for the first time, electrospun nanofiber mats decorated with in-house synthesized silver (Ag(+)) ion exchanged zeolites that function as molecular delivery vehicles. LTA-Large zeolites with a particle size of 6.0 μm were grown on the surface of the cellulose nanofiber mats, whereas LTA-Small zeolites (0.2 μm) and three-dimensionally ordered mesoporous-imprinted (LTA-Meso) zeolites (0.5 μm) were attached to the surface of the cellulose nanofiber mats postsynthesis. After the three zeolite/nanofiber mat assemblies were ion-exchanged with Ag(+) ions, their ion release profiles and ability to inactivate Escherichia coli (E. coli) K12 were evaluated as a function of time. LTA-Large zeolites immobilized on the nanofiber mats displayed more than an 11 times greater E. coli K12 inactivation than the Ag-LTA-Large zeolites that were not immobilized on the nanofiber mats. This study demonstrates that by decorating nanometer to micrometer scale Ag(+) ion-exchanged zeolites on the surface of high porosity, hydrophilic cellulose nanofiber mats, we can achieve a tunable release of Ag(+) ions that inactivate bacteria faster and are more practical to use in applications over powder zeolites.

Ni2+-ion-exchanged dealuminated clinoptilolite: A superior adsorbent for deep desulfurization

A superior adsorbent for the deep desulfurization of liquid fuels has been developed. Clinoptilolite zeolite exhibits a very favorable adsorption isotherm for thiophene, benzothiophene, dibenzothiophene and iso-propyl mercaptan (iso-octane as solvent) upon dealumination with oxalic acid and further ion-exchange with Ni2+. This is while the raw zeolite and the Ni2+-ion-exchanged raw zeolite adsorb benzothiophene and dibenzothiophene molecules scarcely. The effect of oxalic acid molarity and time of reaction on the chemical composition, crystallinity and adsorption capacity of benzothiophene and dibenzothiophene has been investigated in the first step (screening tests). The treated samples have been characterized by X-ray diffraction, X-ray fluorescence, Fourier transform Infra-red, N2 adsorption, transmission electron microscopy and thermal gravimetry analysis. The sample exhibiting optimal adsorption characteristics was used for obtaining the adsorption isotherms for the 4 type of sulfur compounds at 20°C. The optimum sample shows an adsorption saturation capacity of 2.7mgSg−1 for large molecules like dibenzothiophene (molecular diameter>8Å), i.e. ca. 2 times that of the not-dealuminated Ni2+-ion-exchanged or raw zeolite. The enhancement achieved for the adsorptive characteristics has been discussed. The optimum sample shows an exceptional regenerability for benzothiophene and dibenzothiophene.

Remediation of Nitrogen-Contaminated Sediment Using Bioreactive, Thin-layer Capping with Biozeolite

ABSTRACTIn situ amendment of nitrogen-contaminated sediment using bioreactive, thin-layer capping (BTC) with biozeolite (i.e., zeolite with heterotrophic nitrifiers as well as aerobic denitrifiers attached) was studied herein. BTC with biozeolite for nitrogen-contaminated sediment management was evaluated through long-term (170 days) sediment incubation laboratory experiments. The results showed that BTC with relatively small dose rates (<10 kg m−2) of biozeolite reduced the total nitrogen (TN) concentration in overlying water by over 90%, so it was effective in reducing the amount of N released from sediment. Higher-dose rates of biozeolite capping achieved an even higher removal efficiency. With the DO concentration of 1.5 ∼ 6.5 mg L−1 in overlying water, the reduction efficiency of TN in overlying water using BTC was higher than that less than 1 mg L−1. In BTC systems, biological regeneration (i.e., heterotrophic nitrifiers attached to zeolite can regenerate the zeolite ion exchange capacity for ammonium) occurred in biozeolite which was saturated with ammonium during the nitrification period. In addition, TN contents in surface sediment in BTC systems were reduced at different levels after the experiment. These findings indicate that the BTC can be a feasible remedial approach to reduce N in overlying water and sediment in eutrophic water bodies. In the BTC, N load was reduced by the added biozeolite through adsorbing ammonium (NH4+-N), converting NH4+-N into nitrate nitrogen (NO3−-N) and nitrogen gas (N2), and assimilating inorganic nitrogen.

A comparative analysis of the protonated and copper exchanged mordenites with SiO&lt;SUB align="right"&gt;2/Al&lt;SUB align="right"&gt;2O&lt;SUB align="right"&gt;3 molar ratio equal to 10

Ion-exchange zeolites are the starting materials for the synthesis of nanocomposites. Moreover, they are of great interest in themselves, because cations in zeolites, and especially cations of transition metals, are the active catalytic sites. Copper-exchange zeolites are known as very effective deNOx catalysts. Although these compounds have been extensively studied in the last decade, the localisation of the copper ions in the zeolite matrix and their state are not fully determined. Here, we report on the results of our complementary study by various experimental methods, such as thermal analysis, nuclear magnetic resonance (NMR), electronic paramagnetic resonance (EPR), and theoretical density functional calculations of protonated and copper-exchanged mordenites with the molar SiO2/Al2O3 ratio equal to 10.

CATALYTIC PROPERTIES OF NANOMETRIC ZEOLITE X CONTAINING METHYLAMMONIUM CATIONS

The reduction of zeolite particle is one of the main features currently searched; it is due to the catalytic gains that these materials come in some reactions. In this work two faujasite zeolites of type X were evaluated, a micrometer and nanometric. Zeolites in sodium form were exchanged ionically with methylammonium cations. These materials were evaluated as catalysts in the Knoevenagel condensation reaction. Steric impediments restricted the ion exchange in the micrometer zeolite and have become more predominant due to the increase in the volume of cations. In nanometric sample such impediments were less evident due to the reduction of the particles provide greater accessibility to exchangers cations to inaccessible sodium in micrometer zeolite. The best catalytic performances were achieved with zeolites containing the monomethylammonium cation. The increased of the accessibility and diffusion of the reactants and products through the pores of the nanometric zeolite provided the best butyraldehyde conversions independent the exchanger cation

Selective Production of Aromatics from 2-Octanol on Zinc Ion-Exchanged MFI Zeolite Catalysts

The aromatization of 2-octanol derived from castor oil as a byproduct in the formation of sebacic acid was investigated on various zeolite catalysts. Zn ion-exchanged MFI (ZSM-5) zeolites with small silica/alumina ratios and zinc contents of 0.5 to 2.0 wt. % were determined to exhibit good and stable activity for the reaction at 623 to 823 K. The yield of aromatics was 62% at 773 K and the space velocity 350 to 1400 h−1. The temperature and contact time dependences of the product distributions indicated the reaction pathways of 2-octanol→dehydration to 2-octene→decomposition to C5 and C3 compounds→further decomposition to small alkanes and alkenes→aromatization with dehydrogenation. Alcohols with carbon numbers of 5 to 8 exhibited similar distributions of products compared to 2-octanol, while corresponding carbonyl compounds demonstrated different reactivity.

Synthesis and characterization of Fe-modified zeolite for spin conversion of hydrogen at cryogenic temperature

Fe-modified zeolite was prepared by ion-exchange of zeolite with ferric chloride and calcination, for effective spin conversion of ortho- to-para-hydrogen. Studies carried out using BET, SEM, EDS, and VSM techniques. Results indicated that spin conversion rate showed great dependence on magnetic properties of the composite according to calcination temperature change. For lower sintering temperatures, the samples showed more paramagnetic behavior. As sintering temperature increased, ferromagnetic state increase, while paramagnetic states decreased. The highest spin conversion was observed at paramagnetic state, comparing with ferromagnetic, at lower calcination temperature. Moreover, Fe-modified zeolite showed a superior hydrodynamic property such as the pressure drop ratio of composite to a commercial iron oxide. These composites can be applied in more efficient hydrogen liquefaction processes.

Biomineralization of hydroxyapatite in silver ion-exchanged nanocrystalline ZSM-5 zeolite using simulated body fluid

Silver ion-exchanged nanocrystalline zeolite (Ag-Nano-ZSM-5) and silver ion-exchanged conventional zeolite (Ag-ZSM-5) were synthesized. Zeolites were incubated in simulated body fluid at 310K for different time periods to grow hydroxyapatite in their matrixes. Significant large amount of hydroxyapatite was grown in Ag-Nano-ZSM-5 matrix after incubation in simulated body fluid when compared to Ag-ZSM-5. The resultant material was characterized using X-ray diffraction, N2-adsorption, scanning/transmission electron microscopy, energy dispersive X-ray, and inductively coupled plasma analysis. Mechanical properties such as compressive modulus, compressive strength, and strain at failure of the parent materials were evaluated. Biocompatibility assays suggested that Ag-Nano-ZSM-5 and hydroxyapatite grown in Ag-Nano-ZSM-5 were compatible and did not impose any toxicity to RAW 264.7 cells macrophase and Caco2 cells suggesting considerable potential for biomedical applications such as bone implants.

Removal of ammonium from swine wastewater by zeolite combined with chlorination for regeneration

This study investigated a process using ammonium ion (NH4+) exchange on zeolite in combination with chlorination regeneration for the safe treatment of simulated swine wastewater. Two stages i) 120-min zeolite ion-exchange and ii) 10-min exchanged zeolite regeneration facilitated NH4+ ion removal from wastewater. Solution pH, contact time, adsorbent dosage, and competitive cations were the significant factors influencing the entire process. The effect of competitive cations on NH4+ removal effectively followed the order of preference as Na+>K+>Ca2+>Mg2+ at equivalent concentrations. The chlorination method experimentally removed approximately 99% of the NH4+ exchanged on the zeolite, without remaining NH4+ in the regeneration solution. Our analysis revealed that, in this process, the NH4+ exchanged on the zeolite was first replaced by Na+ and then oxidized to nitrogen gas. Reuse of the regenerated zeolite (GZ) indicated that the removal efficiency of NH4+ ions was equal to that of the fresh zeolite modified with NaCl. Results of kinetic analysis revealed that the NH4+ exchange on the GZ followed the pseudo-second-order model and the intraparticle diffusion model only for the first 60 min. The ion-exchange isotherm results demonstrated that the Langmuir model provided a slightly more consistent fit to the equilibrium data as compared with the Freundlich model. Repetitive experimental results confirmed that the proposed zeolite recycling process was stable and usable in simulated swine wastewater treatment.

Intensification of ammonia removal from waste water in biologically active zeolitic ion exchange columns

The use of nitrification filters for the removal of ammonium ion from waste-water is an established technology deployed extensively in municipal water treatment, in industrial water treatment and in applications such as fish farming. The process involves the development of immobilized bacterial films on a solid packing support, which is designed to provide a suitable host for the film, and allow supply of oxygen to promote aerobic action. Removal of ammonia and nitrite is increasingly necessary to meet drinking water and discharge standards being applied in the US, Europe and other places. Ion-exchange techniques are also effective for removal of ammonia (as the ammonium ion) from waste water and have the advantage of fast start-up times compared to biological filtration which in some cases may take several weeks to be fully operational. Here we explore the performance of ion exchange columns in which nitrifying bacteria are cultivated, with the goal of a “combined” process involving simultaneous ion-exchange and nitrification, intensified by in-situ aeration with a novel membrane module. There were three experimental goals. Firstly, ion exchange zeolites were characterized and prepared for comparative column breakthrough studies for ammonia removal. Secondly effective in-situ aeration for promotion of nitrifying bacterial growth was studied using a number of different membranes including polyethersulfone (PES), polypropylene (PP), nylon, and polytetra-fluoroethylene (PTFE). Thirdly the breakthrough performance of ion exchange columns filled with zeolite in the presence of aeration and in the presence of nitrifying bacteria was determined to establish the influence of biomass, and aeration upon breakthrough during ammonium ion uptake.The methodology adopted included screening of two types of the naturally occuring zeolite clinoptilolite for effective ammonia removal in continuous ion-exchange columns. Next, the performance of fixed beds of clinoptilolite in the presence of nitrifying bacteria is compared to that in columns in which only ion exchange is occurring. The aeration performance of each of the chosen membranes was compared experimentally using a newly developed membrane support module which is also described. Comparison of ammonia removal in columns equipped with in-situ aeration using each membrane was undertaken and the breakthrough characteristics determined. The results showed that ammonia removal in the presence of the nitrifiers was significantly intensified. Column operation with membrane aeration showed further enhancement of ammonia removal. The greatest enhancement was observed in the case of the polyethersulfone membrane (PES). It is concluded that combined nitrification and ion-exchange is significantly intensified in packed columns by in-situ aeration using a novel membrane module. There is significant potential for extending the ion-exchange cycle time and thus potential cost reduction.

Side-chain alkylation of toluene with methanol over boron phosphate modified cesium ion-exchanged zeolite X catalysts

A series of boron phosphate (BPO4) modified ion-exchanged CsX zeolites, prepared by impregnation method, were characterized by a variety of means and utilized as catalysts for the side-chain alkylation of toluene with methanol. Both BPO4 and Cs species are highly dispersed on the surface/channel of the BPO4/CsX zeolites. The addition of a small amount of BPO4 has no obvious effect on the basic strength of catalysts, but decreases the number of basic sites slightly. Meanwhile, more weak Lewis acidic sites appear with the increasing BPO4 loading. Compared with CsX, the BPO4 modified CsX catalysts exhibit lower ability for the adsorption/activation of methanol to produce surface intermediates like formaldehyde, unidentate formate and bidentate formate. Catalytic reaction results showed that modification of CsX with boron phosphate can improve both the conversion of toluene and the selectivity of styrene. The inhibition role in producing the unfavorable bidentate formate might be a key factor for finally resulting in the improvement of the catalytic properties of BPO4/CsX catalysts for the side-chain alkylation of toluene with methanol.

Catalytic Wet Peroxide Oxidation of Olive Oil Mill Wastewater over Zeolite Based Catalyst

Olive oil mill wastewater (OOMW) – the liquid waste generated in the process of olive oil extraction contains significant amounts of phenolics. Their high polluting charges that are measured in BOD5 and COD levels up to 35 g dm -3 and the presence in the concentrations up to 10 g dm -3 are of special concern to the environment. These compounds make OOMW biorefractory in nature and unsusceptible to a conventional biological treatment. Reducing their toxicity prior to the conventional treatment is therefore of the uttermost importance. The non-selective catalytic wet peroxide oxidation (CWPO) process is one of the methods that can be used for that purpose in practice. With the use of catalysis the process can be successfully operated under mild conditions with low energy consumption. In this work, the influence of the reaction parameters and the catalyst preparation method on the activity and stability of zeolite (13X) based catalyst in the reaction of hydrogen peroxide oxidation of phenolic compounds present in wastewater from industry for processing olives and olive oil was examined. The reaction was carried out in a batch reactor at different stirring speed, particle sizes, temperatures, catalyst loadings and initial concentrations of hydrogen peroxide. The catalyst Cu/13X was prepared by ion exchange of commercial 13X zeolite. Characterization of the catalyst included N2 physisorption, XRD, TPD-CO2 and FTIR-Pyridine desorption. In order to increase the catalyst’s stability, it was subjected to a thermal post-synthesis treatment at 1273 K. The justification for post synthesis treatment of the catalyst is reflected in the enhanced stability of the catalytically active material which is removed from the carrier, i.e. larger resistance of Cu/13X - K1273 to leaching. Examining the effect of the mixing rates and catalyst particle sizes on reaction rate it was found that the reaction is carried out in the kinetic regime, with the total phenols content diminished by more than 80 % with a 20 % decrease in wastewater’s TOC content and leaching below 3 wt. %.

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.