Ions In Zeolite Research Articles

Activation of Pd/SSZ-13 catalyst by hydrothermal aging treatment in passive NO adsorption performance at low temperature for cold start application

Pd/SSZ-13 catalysts after hydrothermal aging (HTA) treatment at 750°C for 25h showed enhanced passive NO adsorption performance at temperature below 120°C, which will be suitable for cold start application, although those calcined at 500°C did not possess good NO adsorption capacity irrespective of the preparation methods such as incipient wetness impregnation, wet impregnation, ion-exchange, and solid state ion exchange. NO adsorption ability of HTA treated Pd/SSZ-13 samples increases gradually as a function of the metal content, up to 2wt% Pd loading, and then decreased implying that there is an optimum chemistry between the metal and zeolite support. Combined H2-TPR and Pd XAFS results clearly demonstrate that PdO mainly existed over the fresh samples, whereas HTA treated samples contained ionic Pd2+ species, indicating the redistribution of PdO into highly dispersed Pd2+ species within the SSZ-13 structure arising from HTA treatment. Such phenomenon was visually confirmed by comparative STEM-EDS analysis of fresh and HTA Pd/SSZ-13 samples. DRIFT results display the formation of two nitrosyl complexes adsorbed on Pd2+ ions, which are directly related to two desorption peaks of NOx at 250 and 400°C. All combined results provide the unambiguous evidence about the generation of Pd ions in SSZ-13 zeolite induced by HTA treatment, which play as the active sites for NO adsorption at low temperature.

Enhancing the catalytic activity of hydronium ions through constrained environments

The dehydration of alcohols is involved in many organic conversions but has to overcome high free-energy barriers in water. Here we demonstrate that hydronium ions confined in the nanopores of zeolite HBEA catalyse aqueous phase dehydration of cyclohexanol at a rate significantly higher than hydronium ions in water. This rate enhancement is not related to a shift in mechanism; for both cases, the dehydration of cyclohexanol occurs via an E1 mechanism with the cleavage of Cβ–H bond being rate determining. The higher activity of hydronium ions in zeolites is caused by the enhanced association between the hydronium ion and the alcohol, as well as a higher intrinsic rate constant in the constrained environments compared with water. The higher rate constant is caused by a greater entropy of activation rather than a lower enthalpy of activation. These insights should allow us to understand and predict similar processes in confined spaces.

Stabilizing Low‐Silica Zeolites through Aluminum Sulfate Assisted Cannibalistic Dealumination

AbstractA versatile dealumination strategy was proposed to stabilize low‐silica zeolites through cannibalistic interaction between the host framework Al (FAL) and the guest aluminum salt. It is possible to capture selectively the FAL and Na ions in NaY zeolite by employing a special external Al source such as aluminum sulfate as the dealuminating agent. This unique postmodification reduces the FAL amount efficiently and converts the chemically reacted Al species into a γ‐alumina support for the catalytically active component of zeolite, which avoids wasting Al sources. Possessing greatly enhanced hydrothermal stability, newly generated intracrystal mesopores, as well as an optimized distribution of FAL, the resultant dealuminated Y zeolite catalysts can be used practically in heavy oil cracking.

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.

Structural comparison of partially dehydrated partially Co2+-exchanged zeolites X (FAU, Si/Al = 1.40) and Y (FAU, Si/Al = 1.70)

The structures of partially dehydrated and partially Co2+-exchanged zeolites X (Si/Al = 1.40) and Y (Si/Al = 1.70) were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd $$\overline{3}$$ m and were refined to the final error indices R 1/wR 2 = 0.0773/0.2152 and 0.0683/0.2184, respectively. Their unit-cell formulas are |Co26.1Na21(H3O)7.1(H2O)14.2|[Si112Al80O384]-FAU (a = 24.7892(2) A) and |Co29.3Na6.2(H3O)5.9(H2O)5.9|[Si121Al71O384]-FAU (a = 24.7346(2) A), respectively. In the structure of Co2+-X, Co2+ ions occupy sites I′, II′, II, and III′; the Na+ ions are at sites I′ and II. In the structure of Co2+-Y, Co2+ ions occupy sites I′, II′, II, and III′; the Na+ ions are at site I′. Because of the low pH of the Co2+ exchange solution, some H3O+ ions are observed in both structures. The number of Co2+ ions in zeolite was increased slightly as Si/Al ratio increased, and Na+ content and the unit cell constant of the framework were decreased.

Ion Exchange Dependent Electroactive Phase Content and Electrical Properties of Poly(vinylidene fluoride)/Na(M)Y Composites

Different metal ion exchanged NaY zeolite, Na(M)Y, were used to prepare poly(vinylidene fluoride) based composites by solvent casting and melting crystallization. The effect of different metal ion exchanged zeolites on polymer crystallization and electrical properties was reported. Cation–framework interactions and hydration energy of the cations determined that K+ is the most efficient exchanged ion in NaY zeolite, followed by Cs+ and Li+. The electroactive phase crystallization strongly depends on the ions present in the zeolite, leading to variations of the surface energy characteristics of the Na(M)Y zeolites and the polymer chain ability of penetration in the zeolite. Thus, Na(Li)Y and NaY induce the complete electroactive γ-phase crystallization of the crystalline phase of PVDF, while Na(K)Y only induces it partly and Na(Cs)Y is not able to promote the crystallization of the electroactive phase. Furthermore, different ion size/weight and different interaction with the zeolite framework result in significant variations in the electrical response of the composite. In this way, iinterfacial polarization effects in the zeolite cavities and zeolite–polymer interface lead to strong increases of the dielectric constant on the composites with lightest ions weakly bound to the zeolite framework. Polymer composites with Na(Li)Y show the highest dielectric response, followed by NaY and Na(K)Y. Zeolite Na(Cs)Y contributes to a decrease of the dielectric constant of the composite. The results show the relevance of the materials for sensor development.

The effect of structure directing agents on the ordering of fluoride ions in pure silica MFI zeolites.

The effect of different sizes of structure directing agents on the ordering of the fluoride ions in pure silica MFI zeolites has been determined using magic angle spinning solid state NMR. By synthesizing fluoride containing pure silica MFI zeolites using methyltributylammonium cations as the structure directing agent, it has been possible to change the type of ordering seen for the fluoride ions at room temperature from the previously reported dynamic to static disorder. An initial mechanism for how this fluoride ordering occurs is suggested based upon the coulombic interaction between the positive charge on the nitrogen and the negative fluoride ion, within the zeolite framework, with different sizes of tetraalkylammonium cations.

Unusual coordination state of cobalt ions in zeolites modified by aluminum chloride.

Co- and Al-modified zeolites (Al-Co-ZSM-5) were prepared by solid-state ion exchange with cobalt acetate or chloride, followed by AlCl3 immobilization from anhydrous toluene solution. Based on data from XRD, X-ray absorption (XANES/EXAFS), X-ray photoelectron spectroscopy and DRIFT spectral studies of adsorbed probe molecules (carbon monoxide, ethane), a new cobalt electronic state, bonded with surface aluminum atoms through oxygen and chlorine atoms, arises on the surface of Al-Co-ZSM-5. A new band at 2192 cm(-1) appears in the DRIFT spectrum, shifted to lower frequencies compared to CO complexes with isolated Co(2+) cations (2205 cm(-1)). Spectral data of the ethane adsorption (new strong bands in the range of 2740-2770 cm(-1)) prove the existence of specific centers of alkane activation on coordinately unsaturated cobalt cations, resulting in the interaction with aluminum chloride.

Low-temperature fabrication of Cu(i) sites in zeolites by using a vapor-induced reduction strategy

Cu(ii) ions in zeolites can be selectively converted to Cu(i) ions at low temperatures using the strategy of vapor-induced reduction.

Equilibrium modeling of ion adsorption based on Poisson–Boltzmann equation

Abstract A phenomenological model representing ion adsorption equilibrium is proposed. It is an extension of the model used to represent surface adsorption, and it is intended to interpret bulk adsorption data. The fundamental equations of the model were established for fluid and solid phases mass balance and for the spatial distribution of ions across the sample. The electric field distribution in the system, modeled on Poisson's equation, and the chemical potential behavior were determined as a function of fluid phase equilibrium concentration. The concentration of ions as a function of electric potential is given by Boltzmann distribution. The proposed model was successfully tested to represent equilibrium adsorption of metallic ions in zeolite, showing results similar to conventional isotherms.

Dehydration of methanol to light olefins upon zeolite/alumina catalysts: Effect of reaction conditions, catalyst support and zeolite modification

The reaction of methanol to propene was studied in a fixed bed reactor using a pelleted zeolite in alumina matrix support catalyst. The effect of reaction conditions (temperature, pressure, space velocity, feed composition), as well as the effect of support to ZSM-5 zeolite ratio on the conversion of methanol to light olefins (C2–C4) was studied. The best catalyst and optimum reaction conditions leading to a maximum yield of C2–C4 were determined. Use of γ-alumina as support improved the catalyst selectivity to propene and light olefins. Zeolite/alumina catalyst with 25wt.% ZSM-5 dispersed in a matrix containing 75% alumina led to highest selectivity to propene and light olefins. ZSM-5 zeolite was modified with phosphorus, Cs, Ca and Fe. The effect of their impregnation on the conversion of methanol and selectivity to light olefins was studied. Modification in all cases increased the shape-selectivity to light olefins. ZSM-5 zeolite ion exchanged by Cs led to highest selectivity to light olefins and particularly propene by changing the acid sites distribution.

Following the movement of Cu ions in a SSZ-13 zeolite during dehydration, reduction and adsorption: A combined in situ TP-XRD, XANES/DRIFTS study

Cu-SSZ-13 has been shown to possess high activity and superior N2 formation selectivity in the selective catalytic reduction of NOx under oxygen rich conditions. Here, a combination of synchrotron-based (XRD and XANES) and vibrational (DRIFTS) spectroscopy tools has been used to follow the changes in the location and coordination environment of copper ions in a Cu-SSZ-13 zeolite during calcinations, reduction with CO, and adsorption of CO and H2O. XANES spectra collected during these procedures provide critical information not only on the variation in the oxidation state of the copper species in the zeolite structure, but also on the changes in the coordination environment around these ions as they interact with the framework, and with different adsorbates (H2O and CO). Time-resolved XRD data indicate the movement of copper ions and the consequent variation of the unit cell parameters during dehydration. DRIFT spectra provide information about the adsorbed species present in the zeolite, as well as the oxidation states of and coordination environment around the copper ions. A careful analysis of the asymmetric T–O–T vibrations of the CHA framework perturbed by copper ions in different coordination environments proved to be especially informative. The results of this study will aid the identification of the location, coordination and oxidation states of copper ions obtained during in operando catalytic studies.

Effective removal of uranium ions from drinking water using CuO/X zeolite based nanocomposites: effects of nano concentration and cation exchange

For the first time, effects of CuO nanoparticles concentration (from 1 to 24.2 wt%) in CuO/NaX nanocomposite and replacing various cations (Ag+, K+, Ca2+, and Mg2+) with Na+ ions in NaX zeolite on removal of uranium ions from drinking water are reported. The removal of uranium was performed under natural conditions of pH, laboratory temperature and the presence of competing cations and anions that are available in tap water of Isfahan city. Characterization of parent NaX zeolite and modified samples were investigated using X-ray fluorescence, X-ray powder diffraction patterns, scanning electron microscopy, and atomic absorption spectroscopy methods. Using Langmuir, Freundlich, and C-models, isotherms of equilibrium adsorption were studied. Results show the removal efficiency and distribution coefficient of NaX zeolite decrease in the presence of other competing anions and cations that exist in drinking water. But, modification of NaX zeolite with various cations and CuO nanoparticles might enhance the ability of X zeolite in removing uranium from drinking water.

Final storage of radioactive cesium by pollucite hydrothermal synthesis

The Fukushima nuclear accident has highlighted the importance of finding a better final storage method for radioactive cesium species. Cs is highly soluble in water, and can easily exchange with other alkali ions in zeolites or clays to form stable complexes. However, Cs+ is released from Cs+ complexes into water when surrounded by an excess of water. Pollucite may be the best final storage option for Cs+, but its typical synthesis requires heating to about 1200°C in air. Here, we show that the hydrothermal synthesis of pollucite can be completed at 300°C in three hours from any zeolite or clay. Furthermore, our procedure does not require ion exchange before synthesis. Radioactive Cs is usually found in complexes with clays. At that time, this method only requires calcium hydroxide, water, and three hours of hydrothermal synthesis, so the process is both inexpensive and practical for large-scale application. Pollucite is an analog of analcime zeolite, and contains a channel system 2.8 Å in diameter, which is formed by 6-oxygen rings. As the diameter of Cs+ is 3.34 Å and each Cs+ exists independently within a separate portion of the channel, Cs+ cannot exit the pollucite framework without breaking it.

Two Different States of Copper Ions in Zeolites

This work is devoted to the study of copper ion positions in zeolite matrices. Copper cations were exchanged in mordenite and zeolite X from aqueous solutions of different copper salts varying their concentrations. Electronic state of copper in ion-exchanged samples exchanged and dried at different temperatures was evaluated by XPS spectroscopy. Depending on conditions of exchange treatment copper was found to be distributed between two different accessible sites in zeolites. These copper ions are stabilized as isolated species with well-defined oxygen coordination polyhedra.

Remarkable acid strength of ammonium ions in zeolites: FTIR study of low-temperature CO adsorption on NH4FER

FTIR spectra of CO adsorbed at 100 K reveal remarkable acid strength of the free NH groups of tridentate ammonium ions in NH4FER zeolite.

Ammonia Removal using the Bed Filtration across the Abundantly Available Clinoptilolite-rich Tuff

The objective of this study was to determine the feasibility at the laboratory and to evaluate the pilot potential in the field operation for ammonia removal out of the drinking water with enhanced ammonia concentration by applying Slovakian clinoptilolite-rich tuff deposited at the domestic municipality Nižný Hrabovec. Detailed technological parameters were determined for the inland clinoptilolite-rich tuff and compared with some other foreign samples including common water treatment adsorption materials like active coke and silica sand. The one zeolite column was able to treat 85 m3 of drinking water with enhanced ammonia concentration up to the limited value of 0.5 mg/L (the laboratory model only a volume of 675 L), what means that the 4 days operated zeolite filter removed from the whole treated volume of water 81 g of ammonia. Any heavy metal concentrations over the hygienic limitation occurred in water treated by clinoptilolite-rich tuff. The 2 h lasted regeneration was sufficient. The aqueous NaCl solution with pH = 9 was used for the zeolite bed regeneration. The increased pH and temperature of regenerant brines positively influenced the ammonia removal during the recovery of regenerant solution using the air stripping.The zeolite ion exchange pilot installation (ZIEPI) with a hydraulic loading rate of 900 L/h was situated than at the field experimental facility of Water Research Institute in Vajnory, the closed vicinity of Bratislava.

A zeolite ion exchange membrane for redox flow batteries

The zeolite-T membrane was discovered to have high proton permselectivity against vanadium ions and exhibit low electrical resistance in acidic electrolyte solutions because of its enormous proton concentration and small thickness. The zeolite membrane was demonstrated to be an efficient ion exchange membrane in vanadium redox flow batteries.

Direct Observation of Cyclic Carbenium Ions and Their Role in the Catalytic Cycle of the Methanol‐to‐Olefin Reaction over Chabazite Zeolites

Carbenium ions in zeolites: Two important carbenium ions have been observed for the first time under working conditions of the methanol-to-olefins (MTO) reaction over chabazite zeolites using (13) C NMR spectroscopy. Their crucial roles in the MTO reaction cycles have been demonstrated by combining experiments and theoretical calculations.

Novel kinetic model of the removal of divalent heavy metal ions from aqueous solutions by natural clinoptilolite

Removal of heavy metal ions from aqueous solutions using zeolites is widely described by pseudo-second order kinetics although this model may not be valid under all conditions. In this work, we have extended approaches used for derivation of this model in order to develop a novel kinetic model that is related to the ion exchange mechanism underlying sorption of metal ions in zeolites. The novel model assumed two reversible steps, i.e. release of sodium ions from the zeolite lattice followed by bonding of the metal ion. The model was applied to experimental results of Cu(II) sorption by natural clinoptilolite-rich zeolitic tuff at different initial concentrations and temperatures and then validated by predictions of ion exchange kinetics of other divalent heavy metal ions (i.e. Mn(II), Zn(II) and Pb(II)). Model predictions were in excellent agreements with experimental data for all investigated systems. In regard to the proposed mechanism, modeling results implied that the sodium ion release rate was constant for all investigated metals while the overall rate was mainly determined by the rate of heavy metal ion bonding to the lattice. In addition, prediction capabilities of the novel model were demonstrated requiring one experimentally determined parameter, only.