Ion-exchanged Zeolite Research Articles

Equilibrium and Kinetic Insights into the Comprehensive Investigation of CO2, CH4, and N2 Adsorption on Cation-Exchanged X and Y Faujasite Zeolites.

The adsorption equilibria and kinetic performance of CO2, CH4, and N2 on pelletized cation-exchanged faujasite zeolites (with alkali, alkaline earth, and transition metal ions) have been investigated by an innovative volumetric apparatus simultaneously. The standard instrumental analytical techniques, including X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), and atomic absorption spectroscopy (AAS), were utilized to characterize binder-free modified zeolites. EDX and AAS analyses revealed that the ion exchange was successfully achieved. The results indicate that the type of cation present in the zeolite framework and the Si/Al ratio can have a significant impact on the adsorption capacity and kinetic performance. The obtained isotherms were determined by three isotherm models, and the Langmuir-Freundlich (Sips) model was found to show the best agreement with the experimental isotherm data for all gases. The CO2 uptakes of KX, MgX, and CaX reached 4.13, 4.79, and 5.48 mmol/g, respectively. The effective binary and kinetic selectivities of CO2/CH4 and CO2/N2 were also calculated. Among all samples, KX showed the highest CO2/CH4 and CO2/N2 selectivities of 54.46 and 91.62, respectively. Pseudo-first-, pseudo-second-order, and Avrami kinetic models were fitted to the experimental kinetic data to analyze the adsorption kinetics. Finally, the macropore diffusion coefficient (Dp) and microporous diffusional time constant (Dc/rc2) were estimated by correlating the micropore-macropore kinetic model with the experimental fractional uptake curves. Among the ion-exchanged zeolite samples, the K+ form exhibits a suitable performance in terms of kinetic behavior and adsorption capacity.

Catalytic upgrading of lignin-derived bio-oils over ion-exchanged H-ZSM-5 and H-beta zeolites

H-ZSM-5 and H-Beta zeolites ion-exchanged with alkali (Na+ and K+) and alkaline-earth (Mg2+) metals have been explored for the catalytic fast pyrolysis of lignin. Incorporating these metals led to a significant change in the acidic properties of the parent zeolites turning into mostly Lewis-type acidity. Catalytic fast pyrolysis experiments of lignin were performed in a fixed bed reactor with ex-situ configuration operating at 550 °C (thermal zone) and 450 °C (catalytic zone), atmospheric pressure and under a nitrogen flow. Moreover, two catalysts to lignin mass ratios (C/L = 0.2 and 0.4) were studied. Compared with non-catalytic tests, the use of parent zeolites caused a decrease in the bio-oil* (water-free basis) yield due to enhanced production of gases, water, and the coke deposition on the catalyst. In addition, the quality of bio-oil* was improved since it presents a lower oxygen content regarding the thermal test. H-Beta zeolite showed a higher deoxygenation degree than H-ZSM-5, but the latter exhibited a higher share of light components in the bio-oil* that can be detected by GC-MS analyses. Both catalysts promoted the production of light oxygenates, aromatics, and oxygenated aromatics. Regarding the effect of the incorporation of metals, oxygenated aromatic compounds were the predominant family in the bio-oil* obtained with all ion-exchanged zeolites. Likewise, significant differences were observed among the catalysts regarding the main components of this family (alkylphenols, guaiacols, syringols, catechols, and methoxybenzenes), achieving guaiacols concentrations in bio-oil* near to 24 wt.% for NaH-ZSM-5 and KH-ZSM-5 catalysts, and alkylphenols concentrations close to 16 wt.% for MgH-Beta and KH-Beta zeolites.

Low-temperature catalytic dechlorination of model plastic pyrolytic oil over zeolite catalysts

Catalytic dechlorination of model plastic pyrolytic oil was investigated over different types of zeolites and ion-exchanged 13X zeolites at the low temperatures of 20–120 °C. Among different types of parent zeolites (13X, β, MCM-41), 13X had the highest catalytic dechlorination performance. After ion exchange of 13X with Ag+, its catalytic dechlorination performance was significantly enhanced, and the chlorine removal over Ag-13X reached 97.2 % after reaction for 5 h at 120 °C. The characterization results indicated that the acidity of the zeolite governed its catalytic dechlorination performance, and higher acid amount and stronger acid strength are preferred. Different types of chlorinated compounds followed different dechlorination mechanisms. The primary chlorinated alkanes (e.g., 1-chlorooctane) underwent nucleophilic substitution by the surface –OH groups or H2O to form alcohols and HCl, or dehydrochlorination reaction to produce olefins and HCl, while higher chlorinated alkanes with adjacent hydrogen (e.g., chlorocyclohexane) mainly underwent dehydrochlorination reaction to produce olefins and HCl. Chlorinated aromatics (e.g., chlorobenzene) was removed mainly by physical adsorption. Ag-13X showed good stability, and the chlorine removal still retained 72.1 % after 102 h on stream. After four dechlorination-regeneration cycles, the chlorine removal had only a slight decrease due to the partial collapse of its structure and slight loss of its acid amount.

Large-scale synthesis of 3D ordered microporous carbon at low temperature using cobalt ions exchanged zeolite Y as a template

Zeolite-templated carbons (ZTCs) have a unique three-dimensional (3D) ordered microporous structure and an extra-large surface area, and have excellent properties in adsorption and energy storage. Unfortunately, the lack of efficient synthesis strategies and the difficulty of doing this on a large-scale have seriously limited their development. We have developed a large-scale simple production route using a relatively low synthesis temperature and direct acetylene chemical vapor deposition (CVD) using Co ion-exchanged zeolite Y (CoY) as the template. The Co2+ confined in the zeolite acts as Lewis acid sites to catalyze the pyrolysis of acetylene through the d-π coordination effect, making carbon deposition occur selectively inside the zeolite at 400 °C rather than on the external surface. By systematically investigating the CVD temperature and time, the optimum conditions of 8 h deposition at 400 °C produces an excellent 3D ordered-microporous structure and outstanding structure parameters (3 000 m2 g−1, 1.33 cm3 g−1). Its CO2 adsorption capacity and selectivity are 2.78 mmol g−1 (25 °C, 100 kPa) and 98, respectively. This simple CVD process allows the synthesis of high-quality ZTCs on a large scale at a low cost.

Examining the impact of different anions in Cu precursors on sulfur adsorption through zeolites with Cu ion-exchange

The majority of hydrogen is generated by converting hydrocarbons, with natural gas reforming accounting for over 50% of the total hydrogen production. However, the utilization of natural gas in generating hydrogen causes catalyst deactivation during the reforming process because of presence of sulfur compounds as odorants in commercial natural gas. Therefore, the removal of sulfur compounds from natural gas should be prioritized before its application in hydrogen production. Adsorption using Cu-ion-exchanged zeolites is an effective method for removing sulfur compounds from natural gas. In this study, the adsorptive desulfurization performance of tetrahydrothiophene (THT) was evaluated using pristine NaY and Cu-ion-exchanged Y zeolites. In particular, the effects of anions in the Cu compounds used for the ion exchange of zeolites were investigated using three Cu precursors (Cu(NO3)2, Cu(Ac)2, and CuSO4). Among the tested zeolite adsorbents, the NaY zeolite ion-exchanged with Cu(Ac)2 exhibited the highest adsorption uptake, whereas the NaY zeolite ion-exchanged with CuSO4 demonstrated the lowest adsorption uptake for THT. The analytical results indicated that following the exchange of Cu ions, a rearrangement of Si and Al was observed within the zeolite framework, resulting in the Si site distribution. The rearrangement of the framework and distribution of Si sites was influenced by the anions present in the Cu precursors. In addition, it was observed that Cu2+ primarily occupied two locations within the zeolite, namely the supercage and the sodalite cage, and the distribution of Cu2+ between these two sites varied amongst the Cu-ion-exchanged zeolites. This discrepancy was linked to the adsorption uptake for THT.

Ambient temperature NO2 removal by adsorption on transition metal ion-exchanged chabazite zeolites

NO2 as a toxic air pollutant causes serious health problems and contributes to environmental damages, which needs to be abated to a harmless level urgently. However, the abatement of low-concentration NO2 pollution under ambient temperature is challenging due to the ineffectiveness of the state-of-the-art deNOx technologies which are only efficient at elevated temperatures (>300 °C). Adsorption is herein studied as an alternative approach for ambient temperature NO2 removal, using transition metal (i.e., Ag+, Cu2+, Co2+, Ni2+, Zn2+, In3+, and Ce3+) ion-exchanged chabazite (CHA) zeolites with different Si/Al ratios (Si/Al = 2, 6, and 12). NO2 is dominantly physiosorbed on the as-prepared samples, which enables the reversible adsorption in cyclic adsorption process. Ni2+ and Co2+ as active adsorption sites showed elevated affinity to NO2 molecules, which was attributed to the formation of Pi-back bonding via the donation of the electrons in dz2 orbital of the metal ions to Pi × orbitals of NO2 molecule, as evidenced by the changes in the electron occupancies in the orbitals of both transition metal ions and NO2 molecule upon NO2 adsorption (DFT calculation). Co2+ ion-exchanged CHA with Si/Al ratio of 2 (Co2+-2-L) showed an outstanding NO2 capacity of 4.65 mmol/g, with a stable NO2 removal performance verified by the adsorption-desorption cycles. The NO release amount of our adsorbents (<14%) was lower than other reported materials and can be further reduced by our designed double-bed adsorber. This study provides new fundamental knowledge in developing zeolite-based Pi-back bonding adsorbents for NO2 removal, which not only is of timely significance for developing sought-after technologies for NO2 abatement, but also provides a model adsorbent for the adsorptive removal of other molecules with Pi bonds (e.g., CO, NO, etc.)

Direct synthesis of high silica SSZ-16 zeolite with extraordinarily superior performance in NH3-SCR reaction

The development of Cu ion-exchanged small-pore zeolites with excellent performance and high hydrothermal stability in NH3-SCR reaction is of great importance. However, many frameworks of the small-pore zeolites are Al-rich, for instance, Cu-SSZ-16 zeolite with Si/Al ratio always no more than 5, showing relatively low hydrothermal stability. In this work, inspired by theoretical calculation for the interaction between organic structural directing agents (OSDAs) and zeolite framework, high silica SSZ-16 zeolite with Si/Al ratio at 6.7 was directly synthesized using an economical diquaternary alkylammonium cation as an OSDA. After exchanged with Cu ion, the Cu-SSZ-16 catalyst shows extraordinarily superior performance in NH3-SCR reaction even after hydrothermal aging at 900 °C. The designed synthesis combined with excellent performance as well as high hydrothermal stability of the high silica SSZ-16 zeolite might provide an attractive alternative candidate for NH3-SCR catalyst on diesel vehicles and non-road mobile machinery in the future.

In silico engineering of ion-exchanged zeolites for high-performance carbon capture in PSA processes

In this article we employ a multiscale computational framework to design zeolites with competitive performance in post-combustion carbon capture. The efficiency of CO2 capture from flue gas critically depends on the adsorption properties of the adsorbent material. In recent studies, the search for the best performing materials has been predominantly confined to Metal-Organic Frameworks (MOFs), due to the wide diversity in their adsorption characteristics. Inspired by MOFs and their properties, we sought to produce a similar variety in the CO2 isotherms of zeolites. To this end, we modified the properties of the well-known LTA zeolite by varying the Si:Al ratio and the cation composition. Using molecular simulations, we show that these in silico engineered zeolites exhibit a wide range of isotherms for carbon capture. Pressure Swing Adsorption (PSA) simulations using the modified Skarstrom cycle show that structures with the Si:Al ratio ranging from 2.2 to 3.9 can meet the standard requirement of 90 % purity at 90 % recovery for CO2. This performance can be further improved by modifying the cation composition via moderate ion-exchange of Na+ with K+ ions. Several designed structures exhibit performance that is comparable to or even better than the current industrial benchmark, Zeolite l3X, therefore offering interesting alternatives to MOFs as adsorbents for carbon capture in PSA.

Tailoring zeolite ERI aperture for efficient separation of CO2 from gas mixtures

Constructing the metal cation-mediated low-cost inorganic sorbent with high separation efficiency in CO2, N2, and CH4 remains a major challenge. Herein, we developed a series of alkali metal cations (Na+, K+, Rb+, Cs+)-exchanged ERI zeolites and adopted in the separation process of CO2 among the gas mixture. Among the ion-exchanged zeolites, the zeolite K-ERI showed a high adsorption volume of 70.84 cm3g−1 and an IAST selectivity of CO2/CH4: 6254, CO2/N2: 2872 at 298 K, respectively, far outweighed the reported metal cation exchanged zeolites. Combining powder X-ray diffraction crystallography and density functional theory calculations, we unequivocally unveiled that the metal cations located at s8r effectively tailored zeolite aperture, and metal cation-gas molecules interactions synergically restrained the pass-through capacity of CO2 in ion-exchanged ERI framework. Such a unique host–guest interaction governed by metal cations in aluminosilicate zeolite ERI affords a general strategy for gas separation.

Diamine based hybrid-slurry system for carbon capture

Hybrid adsorption-absorption slurry systems are very attractive for CO2 capture, given their ability to simultaneously lower regeneration energy and increase absorption rate and uptake, because of enhanced mass and heat transfer mechanisms. In this work, novel hybrid slurries were formulated from the dispersion of 1 wt.% of solid adsorbents in a water-lean solvent of 30 wt.% of Tetramethyl-1,3-diaminopropane (TMPDA) + 10 wt.% Ethanol (EtOH) for CO2 capture. Different solid particles were suspended in the water-lean solvent such as activated carbon, ion-exchanged zeolite Y (Mg-Y), and polyethyleneimine doped silicas (PEI-SG and PEI-MCM-41). The CO2 uptake of the solid and fluid components of the slurries was confirmed by pH, density, and Fourier transform infrared analysis. The neat water lean solvent reduced the absorption energy by 16 % and slightly increased the CO2 uptake by 0.6 % compared to the aqueous TMPDA solvent. Additionally, the hybrid slurries exhibited further reductions in absorption energy of 10 – 30 % compared to the benchmark TMPDA-based solvents. The PEI-MCM-41-based slurry presented the highest CO2 uptake of 0.33 g CO2.g−1 and lowest regeneration energy of 2261.30 kJ.kg−1 among the studied systems. Additionally, the hybrid slurry exhibited a 21 % reduction in CO2 uptake compared to the benchmark 30 wt.% aqueous monoethanolamine (MEA) and similar capacity to aqueous methyl diethanolamine (MDEA), however, resulting in a far higher reduction in absorption enthalpy of 56 %, and 29 % compared to aqueous MEA and MDEA, respectively. The results obtained here encourage further development and optimization of hybrid slurry systems as potential efficient systems for CO2 capture.

Effects of ion-exchange on the pervaporation performance and microstructure of NaY zeolite membrane

Pervaporation performance of NaY zeolite membranes is improved by ion-exchange with di-valent nitrate salt. Different nitrate salts, including Co(NO3)2, Mg(NO3)2, Zn(NO3)2, Ca(NO3)2, Cu(NO3)2, KNO3, and AgNO3, have great effects on the channel structure and water affinity of the NaY zeolite membrane. When the concentration of nitrate salt, ion-exchange temperature and time are 0.1 mol·L−1, 50 °C and 2 h, the ion-exchange degree order of NaY zeolites is Ag+ > K+ > Ca2+> Zn2+ ≫ Co2+ > Mg2+. Especially, Ag+ and K+ cation exchange degree of NaY zeolites are achieved to 96.54% and 82.77% in this work. BET surface, total pore capacity, pore size distribution and water contact angle of the ion-exchanged NaY zeolites are all disordered by mono- and di-valent cations. Di-valent nitrate salt is favor for increasing the dehydration performance of NaY zeolite membranes by ion-exchange. When the ion-exchange solution is Zn(NO3)2, the total flux variation and separation factor variation of the NaY membrane (M-5) are −45% and 230% for separation of 10% (mass) H2O/EtOH mixture by pervaporation, and the ion-exchanged membranes showed good reproducibility.

TreatmentImprovements of Catalysts for Higher Yield of Catalytic Cracking

Catalytic cracking is the major source of light olefins. And it is proved that some aromatics can also be obtained via catalytic cracking. Products are always impacted by many factors, especially catalysts. After a long time of development of industrial and commercial catalysts, a general kind of catalysts used in FCC (Fluid Catalytic Cracking) process is molecular sieves. Zeolites molecular sieves are normally applied to enhance the products of light olefins and BTX(Benzene-Toluene-Xylene). This paper highlights some methods to improve the zeolites from different perspectives based on those conditions that can affect zeolites. Some characteristics are discussed like structure, acid sites, acidity, etc. Besides, the cost of synthesis and regeneration should be considered as well. Some ideas about the modification of zeolites are summarized in this article like ion exchange of zeolites by rare earth metals or acids, which all prove the great success of improvements of zeolites. Olefin and BTX production increase effectively with these modified catalysts. There will be more kinds of catalysts in the future by combinations and modifications.

Catalytic oxidation performance and ion-exchange of Ti-MWW zeolite membrane with dual organic template agents and potassium carbonate

In the absence of boric acid, the tubular Ti-MWW zeolite membranes are prepared with dual organic template agents and potassium carbonate by secondary hydrothermal synthesis. 12MR cage and 10 MR of the MWW zeolite topology structure is stabilized by TMAdaOH and HMI organic template agents, K+ cations is a critical mineralization agent for preparing Ti-MWW zeolite membrane with bi-layer Ti-MWW zeolites layer in this work. Besides, ion-exchange could greatly improve the catalytic performance of the Ti-MWW zeolite membrane for phenol hydroxylation with H2O2, influences of ammonium salt, ion-exchange time and temperature on the micro-structure and catalytic performance are investigated. The upper network-like Ti-MWW zeolite layer could be dissolved and removed by ion-exchange with 0.5 M (NH4)2SO4 solution at 60 °C for 24 h, and the “lying” Ti-MWW zeolites layer is kept on the mullite support. On the other hand, ion-exchange could promote the transformation of hexacoordinated extra-framework titanium species to tetracoordinated state in the framework, part of K+ cations of Ti-MWW zeolites are replaced with NH4+ cations. Total flux and phenol conversion of the ion-exchanged Ti-MWW zeolite membrane are 14.89 kg·m−2·h−1 and 36.49 % for phenol hydroxylation by H2O2 at 50 °C.

Positive regulation of osteogenesis on titanium surface by modification of nanosized Ca2+-exchanged EMT zeolites

Cell–titanium interactions are of great importance for the clinical success of dental implants, while traditional titanium surfaces are affected by inertness and have poor osteogenicity. In this study, for the purpose of enhanced osteoconductive and osteoinductive properties, titanium (Ti) substrates modified with calcium ion-exchanged nanosized EMT zeolites (Ca 2+ -EMT) were developed and the effect on cell viability, proliferation, osteo-differentiation, and mineralization of MC3T3-E1 cells was systematically and quantitatively examined. For this purpose, firstly, we synthesized and characterized the nanosized EMT zeolites fabricated using a Na 2 O-Al 2 O 3 -SiO 2 -H 2 O precursor system without the organic template. Then calcium ion was exchanged at different levels within nanosized EMT zeolites (Ca 2+ -EMT) and spin-coated onto the Ti surfaces (EMT@Ti, EMT-3@Ti, EMT-6@Ti, EMT-12@Ti, and EMT-18@Ti). Comprehensive characterization was conducted to study the physicochemical properties of as-synthesized specimens. To determine the osteogenic effects of Ti substrates functionalized with Ca 2+ -EMT, we investigated the biological behavior of MC3T3-E1 cells cultured on Ca 2+ -EMT surfaces in vitro with pure Ti and EMT@Ti serving as negative control and experimental control groups, respectively. The results showed that the Ca 2+ was successfully encapsulated in the sodalite cage of the EMT zeolite, while the overall microstructure was not compromised. Enhanced hydrophilicity and roughness were achieved by spin-coating the Ca 2+ -EMT to the surface of Ti specimens. In vitro biological experiments suggested that all Ca 2+ -EMT coated samples possess favorable osteogenicity, as evidenced by the in vitro osteogenic-related biological cell performance. Notably, a dose-dependent manner was detected, where the EMT-12@Ti group exhibited the greatest bone regenerative potential. Meanwhile, the mechanisms of promoting osteoblast differentiation by Ca 2+ regulation were discussed in depth.

Characterization of ion-exchanged zeolites with lithium for Pressure Swing Adsorption (PSA) applications

The method used for the Ion Exchange process to determine the characteristics of the zeolite is refluxing the zeolite using a 4 M LiCl solution for 36 hours at a temperature of 72℃ and calcined at a temperature of 400℃ for 10 hours. XRF characterization results showed natural zeolite Lampung had moderate Si/Al levels with 8.97 and 8.79 for those given lithium, while zeolite 13X had low Si/Al levels with 4.31 and 3.77 for those given lithium. The XRD results show that Lampung's natural zeolite is clinoptilolite and 13X zeolite is NaX. The results of the adsorption test using the PSA tool, namely for natural zeolite Lampung, the highest oxygen value was 21.3% and that was given lithium at 21.2% for the single bed and double bed types. For zeolite 13X, the highest oxygen value was 22% and that given lithium was 24% for the single bed type, and for the double bed type the highest oxygen value was 21.8% and those given lithium were 24.9%.

Front Cover: A Theoretical Investigation of Cu+, Ni2+ and Co2+‐Exchanged Zeolites for Hydrogen Storage (ChemPhysChem 20/2022)

The Front Cover illustrates the application of ion-exchanged zeolites for hydrogen storage in the fuel cell vehicles. The different zoom levels show hydrogen molecule adsorbed on the extra-framework cations (Cu+, Co2+, or Ni2+) in CHA and AEI frameworks. Different levels of detail also represent our atomic level understanding and solution to a macro level problem. Cover design by Olus Ozbek. More information can be found in the Research Article by Olus Ozbek and Bahar Ipek.

Chlorine vs. Sodium Chloride Regeneration of Zeolite Column for Ammonium Removal from an Explosives Impacted Mining Wastewater

There has only been limited research on ammonium removal by zeolites followed by chlorine regeneration; these studies used batch tests and, in many cases, only dealt with single solute solutions as opposed to multi-component ones. To better simulate full-scale applications, this study used a continuous-flow ion exchange (IE) column system to assess the feasibility of chlorine regeneration of a zeolite IE column used for the removal of ammonium from synthetic explosives impacted mining wastewater (EIMWW). Multi-cycle column loading-regeneration tests were used to evaluate and compare the performance of a NaOCl (1000 ppm as free Cl2) solution with that of a standard salt regeneration solution (5% NaCl). In addition, the impact of two loading cycle durations was evaluated. After three operational cycles with 6 h loading phases, the TAN (total ammonia nitrogen) uptake after NaOCl regeneration was almost the same as that obtained with salt regeneration (0.21 meq/g vs. 0.21 meq/g). The zeolite with NaOCl regeneration showed a higher preference for TAN than with NaCl regeneration (Ca:TAN:K = 2.8:2.3:1 vs. 2.5:1.9:1 for the 6 h loading phase); however, the NaOCl regeneration took longer to complete. It was also found that effluent pH, total chlorine level, and free chlorine level during the chlorine regeneration were positively related, seemingly confirming that the ammonium is oxidized to nitrogen gas and producing hydrogen ions. Regardless of the regeneration solution, if one uses a two-column system, with one column online and the other offline, the shorter loading cycles (6 h) yield a substantially higher daily TAN removal rate.

Copper ion-exchanged zeolite X from fly ash as an efficient adsorbent of phosphate ions from aqueous solutions

Zeolite X derived from fly ash was modified with Cu(NO3)2∙3 H2O solutions of various initial concentrations (0.01, 0.05, 0.10, 0.15, and 0.20 M). The obtained materials were investigated by means of XRD, XRF, N2 adsorption-desorption, and pHpzc. The concentration of Cu(NO3)2∙3 H2O significantly affected both the textural and chemical surface properties of the obtained zeolites. The materials were subjected to a series of adsorption experiments to remove phosphate ions from aqueous solutions. The highest adsorption capacity was obtained for zeolite X modified with 0.05 M Cu(NO3)2∙3 H2O solution, and the obtained adsorption capacity was 87.7 mg (PO43-) g−1. The adsorption mechanism was investigated by means of XPS analysis and correlated with the assumptions of kinetic adsorption models. The interaction between phosphate ions and Cu species on the zeolite surface was found to be the guiding mechanism of adsorption. Additional mechanisms, including precipitation as calcium phosphate and electrostatic attraction, should also be taken into account. A single-point adsorption of phosphate ions was also studied to evaluate the effects of adsorbent dose (1, 2, and 3 g L−1) and adsorption temperature (18, 25 and 40 °C). Increased adsorbent dose resulted in a significantly greater removal of phosphate ions for zeolite Cu0.05X (up to 65.4%). The temperature of 25 °C was found to be the most suitable for conducting adsorption of phosphate ions. Leaching test was performed in water to investigate the risk of applying the investigated zeolites in aqueous solutions as potential adsorbents.

Determination of Chemical Kinetic Parameters for Adsorption and Desorption of NH3 in Cu-Zeolite Used as a DeNOx SCR Catalyst of Diesel Engines

Ammonia-based selective catalytic reduction is one of the most effective NOx reduction technologies for diesel engines, but its low NOx reduction efficiency under low-temperature conditions needs further improvement. Previous studies have broadened our understanding of the NH3 adsorption and desorption that occurs in an SCR catalyst of Cu ion-exchanged zeolite. However, many studies conducted to data on the control of the NH3 adsorption and desorption in SCR catalysts have considered a simple chemical reaction related to a single acid site. This study demonstrates a detailed process for determining the chemical kinetic parameters of the adsorption and desorption of NH3 for different types of acid sites of a zeolite catalyst. The determined chemical kinetics parameters will be used for more effective control of the SCR system in future studies.

Unusual water-assisted NO adsorption over Pd/FER calcined at high temperatures: The effect of cation migration

Moisture contained in vehicle exhaust gas normally degrades the capacity and efficiency of Pd ion-exchanged zeolites as NOx adsorbents by competitive adsorption on active sites. Here, we report a counterexample to this general proposition, in which moisture facilitates the storage of NO as a nitrosyl complex on hydrated Pd ions in high temperature calcined FER-type zeolites. Divalent Pd2+ cations upon elevated temperature (>800 °C) calcination occupy sterically constrained cationic position in the zeolite framework, and become inactive for the adsorption of probe molecules such as NO. These ‘hidden’ Pd ions, however, are accessible by NO when the zeolite is hydrated, but readily release NO as dehydration proceeds. Combined systematic in situ infra-red data with X-ray diffraction Rietveld analyses reveal that the high temperature-induced relocation of Pd ions to more stable cationic positions located near 6-membered ring of the ferrierite cage is responsible for this behavior.