Ion-exchanged Samples Research Articles

Location and nature of Cu species in Cu/SAPO-34 for selective catalytic reduction of NO with NH3

Cu/SAPO-34 catalysts have been reported to show much improved activities and durability for selective catalytic reduction (SCR) of NOx. In this work, we examined the nature of Cu species in SAPO-34 catalysts in order to shed light on the active site requirements. Cu/SAPO-34 catalysts, prepared by ion-exchange and precipitation methods, were characterized in detail. The results consistently indicate that Cu species exist predominantly as isolated ions at the exchange sites in the ion-exchanged sample, whereas in the precipitated sample CuO on the external surface is the dominant species. The ion-exchanged Cu/SAPO-34 was found to show superior NH3-SCR activity than the precipitated sample, suggesting that isolated Cu ions at the exchange sites are likely the active sites.

Hydrothermal incorporation of Ce(La) ions into the framework of ZSM-5 by a multiple pH-adjusting co-hydrolysis

Ce and La incorporated ZSM-5 zeolitic materials with different metal loadings were synthesized via the multiple pH-adjusting procedures involving a co-hydrolysis of TEOS (tetraethyl-orthosilicate) with rare earth salts under a strong acidic condition, a further gelation under a weak acidic condition, and a final basic hydrothermal crystallization. Thus obtained Ce(La)-ZSM-5, as well as Ce or La ion-exchanged ZSM-5 samples, were characterized by XRD, SEM, TG, UV–vis, 29Si MAS NMR, FT-IR, N2-physisorption, and elemental analysis. The characterizations provide systematic and complementary evidences to demonstrate the incorporation of Ce(La) ions into the tetrahedral sites of ZSM-5 framework. The upper limits of the rare earth loadings in the synthesis gel and the final product are ca. 50 and 70 of the molar ratio of Si/Ce(La), respectively. It is observed that the synthesized Ce(La)-ZSM-5 zeolites possess an unusual morphology of microspheres that are assembled by numerous cubic prism-shaped nanocrystallines.

CoAl-CrO4 Layered Double Hydroxides as Selective Oxidation Catalysts at Room Temperature

A new combined approach of using layered double hydroxides (LDHs) for both environmental remediation and the derived material as heterogeneous catalyst for selective oxidation is presented. A series of CoAl LDHs with carbonate or nitrate anion in the interlayers was synthesized by two different methods, namely, constant-pH precipitation using NaOH as precipitating agent and homogeneous precipitation by hexamine hydrolysis. The samples were optimized for chromate removal and an uptake of 45 mg Cr/g was obtained for CoAl2-N (CoAl-LDH with Co/Al atomic ratio of 2 and nitrate as interlayer anion by constant-pH precipitation) which was significantly higher than its corresponding carbonate sample that showed 15 mg Cr/g. The thus derived materials after uptake of chromate were explored for solvent free selective oxidation of benzyl alcohol using tert-butyl hydroperoxide as oxidant at room temperature. Among the catalysts screened, CoAl2-N sample after chromate uptake gave 23% conversion with 100% selectivity for benzaldehyde using a catalyst/substrate weight ratio 1:20. The catalyst was recyclable up to four cycles, and the reaction was heterogeneous. The studies revealed that the chromate ion-exchanged sample was more stable and selective as oxidation catalyst than that of surface adsorbed sample. The observed activity of this catalyst was ascribed to the cooperative contribution of Co and Cr.

Synthesis and Electrochemical Properties of Ca-Substituted Li0.44MnO2

Ca-substituted Li0.44MnO2 samples were prepared from the Na-analogs via Na/Li ion-exchange in molten LiNO3 at 270°C. The Ca substitution was confirmed by using XRD, EDX and ICP analyses in not only the precursor sodium compounds but also the ion-exchanged samples. The electrochemical measurements between 2.0 and 4.8 V showed that the initial discharge capacity decreased from 187 mAh g−1 to 127 mAh g−1 due to the Ca substitution. On the contrary, the cycling performance was drastically improved by the Ca substitution; the discharge capacity retention rate increased from 72% in unsubstituted Li0.28MnO2 to 85% in Li0.24Ca0.05MnO2 after 50 cycles. The dQ/dE plots clearly indicated the decrement of the insertion and extraction reaction in the 4 V range by the Ca-substitution.

Surface Flashover Performance of Ion-Exchanged Machinable Glass Ceramics Material in Vacuum

Under the high electric field, discharge sometimes occurs along the surface of solid in vacuum, gas or liquid dielectrics, which is called surface flashover.SiO2-B2O3-K2O-Li2O-Al2O3-ZnO-MgO-F system glass ceramics has great machinability and excellent dielectronic property.This paper tries to study different time of ion-exchanged samples and their microstructures，which affect surface flashover performance of this novel material under the systerm of high voltage in vacuum. Compared to traditional coating method on alumina ceramic, the ion exchange treatment on glass ceramic can produce a tremendous improvement of flashover characteristics. The results show that the 10 hours ion-exchanged glass ceramic enjoys the most prominent insulation strength.Based on the theory of SEEA (Secondary Electron Emission Avalanche), these phenomena can be reasonably explained by the charge carrier injection and transport behaviors.

Catalytic acetalization of carbonyl compounds over cation (Ce 3+, Fe 3+ and Al 3+) exchanged montmorillonites and Ce 3+-exchanged Y zeolites

Under ambient reaction conditions, a one-pot acetalization of carbonyl compounds with methanol was carried out over a series of solid acid catalysts. Ion-exchanged montmorillonite samples were prepared by a metal cation (Ce 3+, Fe 3+ and Al 3+) exchange from the activated K-10 montmorillonite. These materials have been characterized by wide-angle X-ray scattering (WAXS), solid-state nuclear magnetic resonance spectroscopy (solid-state NMR) , temperature programmed desorption of ammonia (NH 3-TPD) and Brunauer–Emmett–Teller (BET) analysis. The catalytic results of montmorillonites were compared with those of H–Y, Ce,Na–Y, Ce,H–Y zeolites, SiO 2 and γ-Al 2O 3. Irrespective of the catalyst, the reaction yields the corresponding dimethoxyacetal in high yield. Comparison of the catalytic activity indicates that the montmorillonite catalysts are the most active catalysts for the reaction. The molecular size of the carbonyl substrates is one of the significant factors in determining the acetalization ability of the catalysts, and the activity of ketones follow the order cyclohexanone > 4-nitroacetophenone > acetophenone > 4-methoxybenzophenone > benzophenone. In the aromatic carbonyl compounds, the electron donor or acceptor properties of the substituents are also critical to the reactivity of the acetophenones and benzaldehydes. The aldehydes considered in the present investigation exhibit an activity order of 4-nitrobenzaldehyde > benzaldehyde > 4-methoxybenzaldehyde, which substantiates that electron-withdrawing groups favor the reaction. The reaction time studies indicate that the montmorillonite catalysts are more resistant to deactivation, predominantly due to the superior pore diffusional properties of these materials compared to microporous zeolites.

Adsorptive and Photocatalytic Removal of Phenol by Layered Niobates Organically Modified Through Intercalation and Silylation

Layered hexaniobate K4Nb6O17 was modified with dodecylammonium ions and octadecyltrimethoxysilane molecules, which were held in the interlayer spaces by electrostatic interactions and covalent attachment to the layers, respectively. Interlayer spacing of the niobate was expanded by incorporation of the bulky organic species. Vapor adsorption isotherms of benzene and water indicated hydrophobic interlayer microenvironments of the organically modified niobates. Both of the modified niobates fairly adsorbed phenol dissolved in water. The photocatalytic activity of hexaniobate allowed the organically modified materials to photocatalytically decompose phenol upon UV irradiation. Decomposition time courses and quantitative analysis of phenol present in the system indicated that the phenol molecules adsorbed on the niobates were preferentially degraded. XRD and IR analyses of the modified niobates indicated that the silylated niobate was more durable than the ion-exchanged sample; the former kept the structure during the photocatalytic process while the latter was partly collapsed.

Silver ion-exchanged sodium titanate and resulting effect on antibacterial efficacy

Surface modification with silver ion is an effective way to reduce infections. In the present work, the effect of silver ion-exchanged sodium titanate on the titanium has characterized by thin film X-ray diffraction analysis (TF-XRD) and high resolution scanning electron microscopy (HR-SEM). Antibacterial activity of silver ion-exchanged sodium titanate on titanium was assessed by the plate-counting method using against Staphylococcus aureus. The results show that silver ion-exchanged samples improve the antibacterial activity depends on NaOH concentration in electrolyte while the titanium oxide layer shows a significant decline. It is also found that the apatite-forming ability of silver ion-exchanged samples was showed after 7 days by immersion in SBF. In conclusion, silver ion-exchange method to the sodium-titanate is favorable to increase the antibacterial activity of titanium surfaces as well as apatite-forming ability.

CO 2 adsorption over ion-exchanged zeolite beta with alkali and alkaline earth metal ions

Zeolite beta with high aluminum content (BEA, Si/Al = 7.4) was synthesized and evaluated as a CO 2 capturing agent after conducting ion-exchange with various alkali and alkaline earth metal ions (Li +, K +, Cs +, Mg 2+, Ca 2+, and Ba 2+). The extent of ion-exchange was confirmed by ICP-AES, and textural properties of the samples were measured by XRD, SEM, and BET surface area measurement. CO 2 adsorption isotherms of the ion-exchanged beta samples up to 101.3 kPa were obtained at 273 and 298 K, and the corresponding heats of adsorption were estimated by the Clausius–Clapeyron equation. CO 2 adsorption capacity increased in the sequence of K + > Na + > Li + > Ba 2 + > Ca 2 + ≒ Cs + > Mg 2 + , and all of the evaluated metal ions showed high adsorption selectivity to CO 2 over N 2. The best performance of K +-exchanged beta was also confirmed by a breakthrough curve analysis. Cyclic CO 2 adsorption–desorption performance of the sample was also studied by TGA in a flow system, exhibiting stable cyclic runs accompanied by complete CO 2 desorption at 473 K.

Chemically modified Ba 6Mn 24O 48 tunnel manganite as a lithium insertion host

The electrochemical behavior of chemically modified tunnel — type Ba 6Mn 24O 48 powder and whiskers has been examined in terms of the lithium intercalation/deintercalation. A maximum overall specific capacity of 136 mAh/g was achieved for the nanostructured form of the proton-exchanged Ba 6Mn 24O 48 phase. This phase is formed by Ba 2+/H + exchange, a process which is also accompanied by Mn dissolution, a commensurate increase in the Mn oxidation state, and an anisotropic shrinkage of the unit cell. Three types of lithium ions were detected in the Li NMR spectra of the chemically and electrochemically lithiated materials. Li resonances at ∼ 380 and 280 ppm, due to sites nearby both Mn 3+/Mn 4+ ions in the large tunnels were seen in the ion-exchanged samples, while resonances at similar locations and at ∼ 100 ppm (due to Li near Mn 3+), were observed in the electrochemically lithiated materials. The investigated materials show potential as “electrochemically-active-and-reinforcing” components, and open up strategy with which to produce composite flexible electrodes for lithium-ion batteries.

Rapid Gasification of Nascent Char in Steam Atmosphere during the Pyrolysis of Na- and Ca-Ion-Exchanged Brown Coals in a Drop-Tube Reactor

Several recent studies on in situ steam gasification of coal suggest a possibility of extremely fast steam gasification of char from rapid pyrolysis of pulverized brown coal. The unprecedented rate of char steam gasification can be achieved by exposing nascent char, that is, after tar evolution (temperature range >600 °C), but before devolatilization (<900 °C), to steam in the presence of Na and/or Ca dispersed in/on the char. In this study, we conducted rapid pyrolysis experiments using ion-exchanged Loy Yang brown coal samples, that is, H-form coal with Na/Ca contents <0.001 wt %, Na-form coal with Na content = 2.8 wt % and Ca-form coal with Ca content = 3.2 wt %. These samples were pyrolyzed in an atmospheric drop-tube reactor at a temperature of 900 °C, inlet steam concentration of 50 vol. %, and a particle residence times of 2.8 s. The char yields from the pyrolysis of Na-form and Ca-form coals were as low as 12 and 33% on the respective coal carbon bases, and accounted for only 18 and 53% of the cha...

Formability and properties of self-standing clay film by montmorillonite with different interlayer cations

Influences of exchangeable interlayer cations were investigated on self-standing film formability, film morphology, and properties of the clay films such as flexibility and gas barrier property. Ion-exchanged montmorillonite samples were prepared by a cation exchange from naturally bearing cation, mostly Na +, to Li +, Mg 2+, Ca 2+, Al 3+, and Fe 2+, 3+. Self-standing films were prepared from aqueous colloidal dispersions of these montmorillonite samples with no additives. The montmorillonite samples with monovalent or divalent cation formed flat self-standing films while the Al-montmorillonite sample produced a distorted film. The Fe-montmorillonite sample formed many separated reddish-brown rod-shaped pieces. Clay film microstructures were different with interlayer cations. The films with monovalent interlayer cations were constructed by the stacking of units with delicately waved thin clay sheets in the whole film, but other films show different morphologies between the upper side and lower side; the upper side is laminated with thin sheets; the lower side is laminated with large thick sheets. The self-standing films’ flexibility and gas barrier property differed according to the interlayer cations. These properties were good in cases of samples with monovalent cations. The innumerable short wave and sheet thinness are considered to foster good flexibility and gas barrier properties. The differences in film formability and properties of the films are attributable to different swellability among samples with different interlayer cations. The montmorillonite samples with monovalent cations swell sufficiently by water, but those with polyvalent cations swell poorly. In the latter case, clay crystals aggregate in water, then the aggregate grows into large particles, creating a film with large particles.

Ion exchanged potassium titanoniobate as photocatalyst under visible light

Potassium titanoniobate (KTiNbO5) was synthesized by solid-state reaction. The potassium ion of KTiNbO5 was exchanged for hydrogen ion in hydrochloric acid, and the sample was heat-treated. The shrinkage of the distance between titanoniobate layers that arise from ion-exchange was observed by using X-ray diffraction. The absorption edges of the UV–Vis spectra for the ion exchanged samples which were treated at higher temperature shifted from ultraviolet region to visible region. The change of binding energy was observed by X-ray Photoelectron Spectroscopy. Photocatalytic property of the ion exchanged and subsequently heat-treated under artificial solar irradiation was less than that of the titanium dioxide. On the other hand, that of the ion-exchanged and heat-treated sample under visible irradiation was better than that of the titanium dioxide.

Preparation of CuNaY zeolites with microwave irradiation and their application for removing thiophene from model fuel

To produce ultralow-sulfur fuels, copper ions have been introduced into the framework of Y zeolite by a novel, simple liquid-phase ion exchange method taking advantage of microwaves irradiation. Removal of thiophene from model fuels were studied over activated copper ion-exchanged zeolite samples using column breakthrough experiments at ambient temperature and pressure. The effects of the microwave irradiating power, duration time and the copper ion concentration in aqueous solutions on the ion exchange level and the structure of copper ion-exchanged zeolite samples were investigated by atomic absorption spectrophotometer, X-ray powder diffraction, N 2 adsorption and scanning electron microscope and X-ray photoelectron spectroscopy. The results demonstrated that ion exchange under microwave irradiation was a more attractive zeolite preparation method compared with conventional ion-exchange process. The maximum exchange level of 75% could be obtained after only 10 min irradiation while the exchange level was 71% after conventional ion exchange for twice and the copper can be better dispersed in zeolite framework under microwave irradiation. Microwave-irradiated CuNaY zeolites could efficiently remove thiophene from model fuel with a high sulfur removal capacity of 1.22 mmol/g.

The formation of double waveguides in a KTP crystal by combining ion exchange with ion implantation

Double waveguides were produced in potassium titanyl phosphate (KTiOPO4 or KTP) by ion exchange in pure RbNO3 at 340 °C for 45 min, and subsequently ion implantation with 500 keV O ions at a dose of 1 × 1015 ions cm−2. By the prism-coupling method the guided mode spectra as well as the refractive index profiles of the ion-exchanged sample were determined. The relative value of the refractive index distribution of the ion implanted KTP sample in the z direction was simulated, which indicates the formation of double waveguides. The field pattern of the propagation light in the waveguide was collected and studied by the end-coupling method. The near-field pattern of two planar operating waveguides was observed, one upon the other. The irradiation damage as well as the Rb distribution was analysed by means of the Rutherford backscattering spectrometry technique.

Strengthening of soda-lime-silica glass by surface treatment with sol–gel silica

In this study, the failure resistance of soda-lime-silica glass was increased by surface treatment with sol–gel silica. Samples annealed and ion-exchanged in KNO 3 for 24 h at 450 °C were considered. Sol–gel silica coating was carried out by dipping the glass samples into a sol suspension prepared by hydrolysis of Si(OEt) 4 in ethanol/water solution. The deposited layer was consolidated in air for 24 h and subjected to mild thermal treatment at 300 °C for 1 h. The surface treatment increased the fracture resistance of annealed glass of about 35 MPa; conversely, ion-exchanged specimens showed an average increase of about 90 MPa. The strengthening effect induced by the surface treatment was attributed to the reduction of the effective crack length generated by the silica coating. The different strength increase between annealed and ion-exchanged samples is discussed in terms of fracture toughness which, for ion-exchanged glass, is not constant, due to the presence of the surface residual stresses and thus the reduction of the crack length due to the silica coating determines a higher strength increase than for annealed glass.

Modification of the structure and properties of SAPO-11 using rare earths

Silicoaluminophosphate (SAPO)-11 molecular sieve was modified by rare earth La and Ce using impregnating and ion-exchanging methods. The RE-modified SAPO-11 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett- Teller (BET), pore-size distribution (PSD), in-situ Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH 3-TPD), and compared with the unmodified SAPO-11 sample. The XRD patterns indicated that after RE modification, especially for the La-exchanged sample, the composition of molecular sieve was changed and the crystallinity decreased. The normalized surface area (NSA) of ion-exchanged samples proved that the unsubstituted metal oxides accumulated inside the SAPO-11 pores. Because of the RE cations that were loaded onto the surface of molecular sieve, which could be regarded as the Lewis acid sites, there was an increase in the amount of Lewis acid sites and a decrease in the Brønsted acid/Lewis acid (B/L) ratio. The ability of RE cations to acquire electrons was weaker than that of Al 3+; therefore, the bond strength of bridged hydroxyl decreased after modification. The total acidity of SAPO-11 decreased after RE modification.

TEM monitoring of silver nanoparticles formation on the surface of lead crystal glass

Silver nanoparticles have been formed on the surface of lead crystal glass by means of (i) ion-exchange of alkaline ions from the glass by Ag+ ions from a molten salts bath, and (ii) silica based sol–gel coatings containing silver. All experimental variables concerning both ion-exchange process and sol–gel coatings application were combined and studied as main parameters governing the reduction of Ag+ ions to Ag0 atoms and further aggregation to form nanosized colloids. The content of thermoreducing agents (arsenic or antimony oxides) in the lead crystal glass was essential to favour the reduction of silver ions to form nanoparticles. Optimal experimental conditions to be used for the obtaining of surface silver nanoparticles were determined. TEM was used as the principal characterisation technique for direct observation of the nanoparticles generated. The size of silver colloids varied in the 20–300nm range for ion-exchanged samples and in the 10–80nm range for sol–gel coated samples.

Effects of ion-exchange on the photoreactivity of ETS-10

This paper describes an investigation by EPR spectroscopy and FTIR spectroscopy of the reactivity of ETS-10 photocatalysts subjected to different ion exchange treatments. Trapped photoelectrons can be detected only in ion-exchanged samples which have been damaged as a result of the ion exchange procedure. UV-irradiation of such samples in the presence of adsorbed organic molecules that scavenge photogenerated holes forms Ti 3+ ions, which transfer the electron to oxygen to form superoxide O 2 − on subsequent addition of O 2. Superoxide ions are also formed when damaged samples are irradiated in O 2. As-synthesised (undamaged) samples of ETS-10 are not photo-reduced when irradiated in the presence of adsorbed organic molecules, but do catalyse a novel photo-polymerisation of ethene; the activity for this reaction depends on the level of stacking faults in the ETS-10. Photo-oxidation of ethene to adsorbed carbonyl compounds occurs most extensively in ion exchanged samples; this is attributed to the generation of photocatalytic sites on the external surface of the ETS-10 as a result of the damage caused by ion exchange.

Electron spectroscopic analysis of silver nanoparticles in a soda-glass matrix

Silver ion-exchanged soda-glass samples as well as various postannealed samples were characterized using X-ray photoelectron spectroscopy (XPS) to find out the chemical states of silver in these samples. The analysis by XPS seems to be not enough to distinguish various chemical states of silver, where, shift in binding energies due to oxidation are less or, comparable to that of overall spectrometer resolutions. To overcome this experimental constraint, here we propose a complete and novel method of chemical analysis making use of the associated Auger transitions and finding the modified Auger parameters of concerned samples. Detail lineshape analysis of the Auger transitions in silver helps further to differentiate the minute variances in the local electronic structure. The analysis seems to provide means to identify intricate chemical phases, which are quite tricky to conclude from other analytical experiments.