Ion-exchanged Zeolite Research Articles

Mixed (Ag+, Ca2+)-LTA zeolite with suitable pore feature for effective separation of C3H6/C3H8

Separating C3H6/C3H8 is a challenging task owing to their similar sizes and boiling points. In this study, we report a sequential and partial Ag+/Ca2+ ion-exchanged zeolite that exhibits ideal C3H6/C3H8 molecular sieving. Moreover, the zeolite exhibited superior C3H6 uptake of 2.37 mmol/g and molecular packing density (∼77% packing of liquid C3H6) at an extremely high C3H6: Ag+ ratio of 21.5 with Ag content as low as 1.18 wt%. The (Ag+, Ca2+) cations were sequentially exchanged into LTAs by comprehensively considering the extra-framework cation distribution and site preferences for different cations. By exchanging Ag+ with Na+ in the extra-framework of LTA, C3H6 can be admitted even at the average LTA apertures of sizes < 4 Å. Meanwhile, exchanged Ag+ also increased the adsorption kinetics of C3H6 by an order of magnitude. Hydrophobic modification on Ca-Ag-LTA was successfully achieved to significantly suppress the competition from water while retaining excellent regenerability in multiple cycles. The strategy of binary ion exchange to delicately tune the pore channels and chemistry and selectively admit molecules with beneficial kinetics might potentially be broadened to other industrial separation processes.

Efficient Conversion of Glucose to Methyl Lactate with Sn-USY: Retro-aldol Activity Promotion by Controlled Ion Exchange.

Sn-USY materials have been prepared through an optimized post-synthetic catalytic metalation procedure. These zeolites displayed, upon ion exchange with alkaline metals, an outstanding activity in the direct transformation of glucose into methyl lactate, yielding more than 70% of the starting glucose as the target product, and an overall combined retro-aldol condensation product yield above 95% in a short reaction time (<4 h). This outstanding catalytic performance is ascribed to the neutralization of Brønsted acid sites, the consequent depression of side reactions, and a higher population of tin open sites in the ion-exchanged Sn-USY zeolites. Reusability tests evidenced some loss of catalytic activity, partially caused by the closing of tin sites, although the use of small amounts of water in the reaction media demonstrated that this deactivation mechanism can be, at least, partially alleviated.

Chemical Affinity of Ag-Exchanged Zeolites for Efficient Hydrogen Isotope Separation.

We report an ion-exchanged zeolite as an excellent candidate for large-scale application in hydrogen isotope separation. Ag(I)-exchanged zeolite Y has been synthesized through a standard ion-exchange procedure. The D2/H2 separation performance has been systematically investigated via thermal desorption spectroscopy (TDS). Undercoordinated Ag+ in zeolite AgY acts as a strong adsorption site and adorbs preferentially the heavier isotopologue even above liquid nitrogen temperature. The highest D2/H2 selectivity of 10 is found at an exposure temperature of 90 K. Furthermore, the high Al content of the zeolite structure leads to a high density of Ag sites, resulting in a high gas uptake. In the framework, approximately one-third of the total physisorbed hydrogen isotopes are adsorbed on the Ag sites, corresponding to 3 mmol/g. A density functional theory (DFT) calculation reveals that the isotopologue-selective adsorption of hydrogen at Ag sites contributes to the outstanding hydrogen isotope separation, which has been directly observed through cryogenic thermal desorption spectroscopy. The overall performance of zeolite AgY, showing good selectivity combined with high gas uptake, is very promising for future technical applications.

Nanoporosity and Isosteric Enthalpy of Adsorption of CH4, H2, and CO2 on Natural Chabazite and Exchanged

This paper describes the isosteric enthalpy through narrow pores at low levels of coverage through adsorption of CO2, CH4, and H2 on pores in natural chabazite exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, and with variable time and temperature of treatment. Experimental data of CO2, CH4, and H2 adsorption were treated by the Freundlich and Langmuir equations. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric enthalpy of adsorption. The exchange with Mg2+ and Na+ favors an increase in the adsorption capacity for CO2. while that of Ca2+ and Mg2+ favor adsorption through to H2 and CH4. These cations occupy sites in strategic positions S4 and S4’, which are located in the channels and nanocavities of these zeolites. The presence of Ca2+ and Mg2+ at S4 and S4′ sites causes increased adsorption into the nanocavities and on the external area of the ion-exchanged zeolites. Depending on the conditions of the exchange treatment, Ca2+ and Mg2+, and Na+ were found to be most favorable, well distributed, and accessible for CO2, CH4, and H2 adsorption.

Access to sodalite cages in ion-exchanged nanosized FAU zeolites probed by hyperpolarized 129Xe NMR and DFT calculations

The accessibility to sodalite (SOD) cages in nanosized zeolite X (FAU-type framework) is tuned by varying the nature and location of extra-framework exchangeable cations (Na+, Li+, Cs+, K+ and Rb+). Hyperpolarized (HP) and EXchange SpectroscopY (EXSY) 129Xe NMR experiments highlight the connectivity between SOD- and super (SUP)-cages, in particular that its diffusion pathway from sodalites to supercages depends mainly on the size and location of extra-framework cations present in the zeolite. These 129Xe NMR results are supported by DFT simulations. Based on the computed adsorption energies of Xe in both SOD and SUP cages of zeolite X with different cationic compositions, it is concluded that xenon penetration in SUP cages is always favorable while the adsorption in the SOD cages is possible only if small cations (Na+, Li+, K+) are present.

Supercritical fluid reactive deposition: A process intensification technique for synthesis of nanostructured materials

Supercritical fluid reactive deposition (SFRD) is a promising process intensification technique for synthesis of a wide variety of nanostructured materials. The enhanced mass transfer characteristics of supercritical fluids (SCFs) coupled with high solubilities of reducing gases in SCFs provide many advantages related to equipment size and time minimization over conventional techniques. Among SCFs, the emphasis has been placed on supercritical CO2 (scCO2) which is non-toxic, cheap and leaves no residue on the treated medium. Moreover, in SFRD, multiple processes such as dissolution, adsorption, reaction, and purification are combined in a single piece of equipment which is an excellent example of process integration for process intensification. In this review, the fundamental thermodynamic and kinetic aspects of the technology are described in detail. The studies in the literature on synthesis of a wide variety of nanostructured materials including supported nanoparticles, films, and ion-exchanged zeolites by SFRD are reviewed and summarized. The applications of these materials as catalysts and sensors are described. The review hopes to lead to further studies on further development of this technology for a wide variety of applications.

Investigation on the influence of modified zeolite molecular sieve on the hydrocarbon adsorbent and adsorption performance during cold-start conditions based on Monte Carlo simulation and grey relational analysis

To discover adsorbents with promising adsorption capability for hydrocarbon catcher, this study numerically investigated the adsorption process of modified MOR, MFI, and CON zeolites utilized in hydrocarbon catcher of hydrocarbon (HC) molecules for hydrocarbon emission control during cold-start. Ethylene (C2H4) and benzene (C6H6) were used as probe molecules in the single-component adsorption simulation. The mixture of methane (CH4), C2H4, propylene (C3H6), propane (C3H8), water (H2O) and C6H6 was used as adsorbate in the multicomponent adsorption simulation. The Grand Canonical Monte Carlo (MC) method was used in the adsorption simulation. Grey Relational Analysis (GRA) method was used to determine the influence degree of zeolite molecular sieve type and environmental conditions on the adsorption capacity of hydrocarbons. The adsorption isotherms of hydrocarbon single component and multicomponent molecules on different silicon-aluminum (Si/Al) ratios and different ion exchange zeolites were studied at various low temperatures and pressures. Results of adsorption simulation present that the best adsorption effect on C2H4 was obtained for the magnesium ion (Mg2+) modified MFI molecular sieve at a Si/Al ratio of 3. The adsorption of C6H6 was better for the Na+ modified molecular sieve at Si/Al ratios of 15 and 7. Mg2+ modified MOR molecular sieve can be given priority when the overall control of hydrocarbon mixture content is required, which has adsorption for all kinds of hydrocarbon molecules and more uniform adsorption performance. The calcium ion (Ca2+) modified MFI molecular sieve is suitable for the condition when exhaust gas contains more C3H6, while Mg2+ modified MFI molecular sieve can be used when there are more C3H8. In GRA, the factors with the greatest influence on the adsorption of the C2H4 component are the type of molecular sieve and the porosity. The most important factors on the adsorption of the C6H6 component are the molecular sieve type and temperature, followed by the porosity. In the adsorption of multicomponent hydrocarbons, porosity has the greatest effect on the adsorption amount, followed by molecular sieve type and Si/Al ratio. In addition, the total adsorption of hydrocarbon molecules will be increased with the Si/Al ratio of the molecular sieve.

The Synergistic Effect of Different Silver Species in Silver Ion-Exchanged Lta Zeolite During the High Selectivity Separation of Ethylene/Ethane

The Synergistic Effect of Different Silver Species in Silver Ion-Exchanged Lta Zeolite During the High Selectivity Separation of Ethylene/Ethane

Copper Ion-Exchanged Zeolite X Derived from Fly Ash for Enhanced Phosphate Removal from Aqueous Solutions

Copper Ion-Exchanged Zeolite X Derived from Fly Ash for Enhanced Phosphate Removal from Aqueous Solutions

In Silico Engineering of Ion-Exchanged Zeolites for High-Performance Carbon Capture in Psa Processes

In Silico Engineering of Ion-Exchanged Zeolites for High-Performance Carbon Capture in Psa Processes

Mn2+-exchanged USY zeolites derived glass for wide-range optical thermometry

Mn2+ activated glass derived from ion-exchanged USY zeolites was prepared by spark plasma sintering (SPS) to investigate its temperature-dependent luminescence properties. The luminescence intensity ratio showed a high sensitivity in the temperature range from 4 K to 548 K. The absolute sensitivity and the relative sensitivity values can reach 2 × 10−2 K−1 and 0.66% K−1 at 498 K, respectively. After 3 consecutive thermal cycles tests, the repeatability was 96.6%, and the temperature uncertainty is less than 0.1 K in the range of 270–548 K. The Mn2+ activated USY-zeolite derived glass with high sensitivity, wide temperature range and high thermal conductivity is promising for remote temperature sensing applications.

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO).

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH3-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH3) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH3 emissions is proposed, NH3 emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH3 oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH3 conversion, high selectivity to N2O and NOx as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.

Strain Development of Selective Adsorption of Hydrocarbons in a Cu-ZSM-5 Crystal.

Zeolites are 3D aluminosilicate materials having subnanometer pore channels. The Lewis basic pores have charge-balancing cations, easily tuned to metallic ions as more chemically active sites. Among the ion-exchanged zeolites, Cu2+ ion-exchanged ZSM-5 (Cu-ZSM-5) is one of the most active zeolites with chemical interactions of Lewis basic compounds. Even though the chemical interactions of hydrocarbons with Cu2+ sites in Cu-ZSM-5 have been tremendously studied in the category of zeolite catalysts, it is not yet thoroughly investigated how such interactions affect the structural lattice of the zeolite. Hydrocarbons with different chemical properties and their relative size can induce lattice strain by different chemical adsorption effects on the Cu2+ sites. In this work, we investigate the internal deformation of the Cu-ZSM-5 crystal using Bragg coherent X-ray diffraction imaging during the adsorption of four hydrocarbons depending on the alkyl chain length, the existence of a double bond in the molecule, linear structure versus benzene ring structure, and so forth. In the three-carbon system (propane and propene), relatively weak chemical adsorption occurred at room temperature and 100 °C, whereas strong adsorption was observed over 150 °C. For the six-carbon system (n-hexane and benzene), strong strains evolved in the crystal by active chemical adsorption from 150 °C. The observations suggest that propene and propane adsorb at the Cu2+ sites from the outer shell to the center with increasing temperature. In comparison, n-hexane and benzene adsorb at both parts at the same temperature. The results provide the internal structural information for the lattice with the chemical interactions of hydrocarbons in the Cu-ZSM-5 zeolite and help to understand zeolite-based chemisorption or catalysis research.

Mono- and di-valent ion exchange of mordenite membranes for dehydration of acetic acid by pervaporation

The conventional Na-mordenite (Na-MOR) zeolite membranes prepared on α-Al2O3 tubes by secondary hydrothermal growth method. To improve membrane performances in dehydration of acetic acid by pervaporation, the Na+ as counter ions in MOR membranes were exchanged by a series of mono- and di-valent cations to adjusted the channel structure and water affinity. Langmuir surface areas for monovalent ion-exchanged MOR zeolites were consistent with the reverse order of ion radii as H+>Li+>Na+>K+>Cs+, while for those exchanged by divalent ions the zeolites surface areas followed the reverse order of hydrated ion radii instead of natural radii as Ba2+>Ca2+>Mg2+. The water adsorption of MOR by mono- and di-valent cations exchange were all disordered, and H+, K+ and Ca2+ exchanged MOR showed higher water capacity than that of Na-MOR. In pervaporation, monovalent ion-exchanged membranes with molecular sieving effect showed higher performances than those of divalent ion-exchanged membranes with augmented steric effect and weakened molecular sieving. Among these membranes, H-MOR showed the largest flux of 3.68 kg m−2 h−1 with a normal separation factor of 472 in pervaporation of 90 wt% acetic acid/water under 348 K due to a larger pore size and higher water adsorption, which were supplemented for acid-treated membranes. To get better separation ability, H+ exchange conditions on MOR membranes were investigated in detail. The optimized H-MOR membrane showed a flux of 1.52 kg m−2·h−1and separation factor of 1443 with good stability for 100 h. A simple water wash with a recovered performance proved a previously reported phenomenon that reduced flux with time was affected by acetic acid blockage.

Insight into solid-state ion-exchanged Cu-based zeolite (SSZ-13, SAPO-18, and SAPO-34) catalysts for the NH3-SCR reaction: The promoting role of NH4-form zeolite substrates

In this paper, Cu-exchanged SSZ-13, SAPO-18, and SAPO-34 were synthesized via a novel green and sustainable solid-state ion-exchange (SSIE) route with excellent NH3-SCR activities, which could simplify the preparation process and reduce the wastewater production in comparison to conventional aqueous ion-exchange route. The results also proved that Cu-exchanged zeolites synthesized by SSIE technology presented higher Cu ion-exchange (IE) levels and better SCR activities than those prepared via the traditional incipient impregnation route. In the case of SSIE, the usage of NH4-form substrates could achieve more Cu2+ ions and fewer CuOx than those H-form substrates since the formation of Cu(NH3)x2+ intermediate could promote the Cu2+ mobility to facilitate Cu2+ occupying IE sites, which was favorable for the SCR reaction. The combined DFT data confirmed the SSIE reaction energy barriers between Cu(NO3)2 and the NH4-form substrates were almost identical, whereas the higher reaction energy was required for H-form substrates. In-situ DRIFTS results manifested the labile species like NH4+, –NH2, NO2–, NO3–, NO2, etc were the reaction intermediates over the catalysts prepared from NH4-form substrates. The Langmuir-Hinshelwood (“L-H”) and Eley-Rideal (“E-R”) mechanisms contributed collectively over both Cu-SSZ-13 and Cu-SAPO-18 in the SCR reaction, however, the “L-H” mechanism dominated over Cu-SAPO-34.

Al ion-exchanged USY in FCC catalyst for high LPG yield

Refineries, especially fluid catalytic cracking (FCC) units are required to increase propylene production because of changing demand from fuels to chemicals in recent years. We have found a promising FCC catalyst for such demand. The FCC catalyst with Al ion-exchanged USY zeolite (catalyst (Al)) has indicated the higher LPG yield without decreasing in the activity. The catalyst (Al) would be suppressing hydrogen transfer reactions between products or intermediates. Moreover, the olefins in the gasoline would be over-cracked to LPG over catalyst (Al) because of strong acidity of Al ion-exchanged USY.

Catalytic and Mechanistic Insights into Side‐Chain Alkenylation of Toluene with Methanol for Styrene Formation

AbstractThe literature on catalytic and mechanistic aspects of the side‐chain alkenylation of toluene with methanol for the formation of styrene on solid base catalysts is reviewed. The development of catalysts and catalysis are described mostly on alkali ion exchange zeolite catalysts with fundamental chemistry related to the side‐chain alkenylation. Mechanistic studies performed from various viewpoints are described. Methods to elucidate the reaction mechanisms are discussed based on the identification of the adsorbed species of the reactants, use of plausible intermediate compounds as reactant, characterization of surface properties to examine the correlation with reaction results, poisoning of the active sites by certain molecules, and theoretical calculations of the energy profile along with the reaction coordinate. These studies are discussed with critical assessments. The review addresses several challenges that prevent the side‐chain alkenylation of toluene with methanol from industrialization which include decomposition of methanol to CO and H2, and co‐production of ethylbenzene. The paper covers mostly literature published during the period from 2000 to early 2021.

Ion-exchanged LTA zeolite derived nepheline phase NaAlSiO4:Eu2+ ceramic phosphor for laser illumination

A reliable yellow phosphor converter that can be efficiently excited by a 405 nm bluish violet laser is in high demand for laser illumination applications. A NaAlSiO4:Eu2+ phosphor with a quantum efficiency reaching 92% was obtained using LTA zeolite as the raw material. NaAlSiO4:Eu2+ ceramics with suitable porosities for laser illumination were prepared from the phosphor powders via spark plasma sintering. The ceramics lost only 2% of the quantum efficiency compared to the powders, maintained good thermal quenching properties (30% drop at 150 °C), and showed good thermal conductivity (2.02 W‧m−1‧K−1). The NaAlSiO4:Eu2+ ceramic with 405 nm bluish violet lasers, with the increase in laser power density to 9.15 W/mm2, exhibited an increasing luminous flux (23.83–70.26 lm) and maintained a stable luminous efficacy (47.7–46.8 lm/W), and the temperature distribution of the ceramic remained uniform and stable under long-time laser irradiation. This indicates that the nepheline-phase NaAlSiO4:Eu2+ ceramic is a promising material for laser illumination.

Adsorption properties of ion-exchanged SSZ-13 zeolite for ethylene/ethane separation

Designing effective cyclic adsorption separation processes, e.g., ethylene/ethane PSA separation, is based on finding an appropriate adsorbent. In this matter, examination of equilibrium and kinetic properties of adsorbents, i.e., isotherms and diffusion coefficients of gasses, is critical. In this study, Na-SSZ-13 zeolite was first synthesized and then ion-exchanged with the Ag+ and Cu2+ cations. Afterward, ethane and ethylene equilibrium and kinetic adsorptions and IAST calculations on the mentioned zeolites were investigated. Results showed that all three adsorbents are ethylene-selective at equilibrium conditions. Ion-exchanging leads to higher adsorption selectivity in Cu2+, while Ag+ cation increases the adsorption capacity without altering the selectivity. Furthermore, ion-exchanging increases the diffusivities of both ethylene and ethane in the following order Ag-SSZ-13>Cu-SSZ-13>Na-SSZ-13.

Experimental and Theoretical Studies of Sonically Prepared Cu–Y, Cu–USY and Cu–ZSM-5 Catalysts for SCR deNOx

The objective of our study was to prepare Y-, USY- and ZSM-5-based catalysts by hydrothermal synthesis, followed by copper active-phase deposition by either conventional ion-exchange or ultrasonic irradiation. The resulting materials were characterized by XRD, BET, SEM, TEM, Raman, UV-Vis, monitoring ammonia and nitrogen oxide sorption by FT-IR and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). XRD data confirmed the purity and structure of the Y/USY or ZSM-5 zeolites. The nitrogen and ammonia sorption results indicated that the materials were highly porous and acidic. The metallic active phase was found in the form of cations in ion-exchanged zeolites and in the form of nanoparticle metal oxides in sonochemically prepared catalysts. The latter showed full activity and high stability in the SCR deNOx reaction. The faujasite-based catalysts were fully active at 200–400 °C, whereas the ZSM-5-based catalysts reached 100% activity at 400–500 °C. Our in situ DRIFTS experiments revealed that Cu–O(NO) and Cu–NH3 were intermediates, also indicating the role of Brønsted sites in the formation of NH4NO3. Furthermore, the results from our experimental in situ spectroscopic studies were compared with DFT models. Overall, our findings suggest two possible mechanisms for the deNOx reaction, depending on the method of catalyst preparation (i.e., conventional ion-exchange vs. ultrasonic irradiation).