FAU Zeolites Research Articles

How may preferential heating of the substrate aid template-free preparation of EMT zeolite and its coatings?

The suitability of the preferential heating of the substrate by conduction for the preparation of coatings of EMT-type zeolites was investigated. For this aim, synthesis experiments were performed by using the substrate heating method and the results were compared to those obtained by conventional synthesis where the substrate is heated by convection. EMT zeolites represent an extreme case of metastability, which renders the preparation of their coatings of notable thickness quite difficult. Various synthesis conditions were tested and the coatings obtained were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), energy dispersive X-ray spectroscopy (EDX) and thermogravimetry (TG). It was determined that template-free preparation of relatively thick EMT coatings (identified as ZSM-3, an intergrowth of EMT and FAU zeolites) was possible by using the substrate heating method. Conventional synthesis also yielded coatings of EMT-type, but with only a few microns thickness, at similar substrate temperatures. The zeolite crystallinity was improved by varying the synthesis conditions. Some coatings exhibited quite high water capacities and low regeneration temperatures, favorable for use in applications, such as adsorption heat pumps.

Ultra-thin zeolite CHA and FAU membranes for desalination by pervaporation

In the present work, ultra-thin zeolite CHA and FAU membranes, with thicknesses of 600 and 500 nm, respectively, were evaluated for desalination by pervaporation at various temperatures. Single gas permeation experiments were employed to verify high quality of the membranes. At 90 °C, the observed water fluxes for CHA and FAU membranes were as high as 24 and 28 kg/(m2‧h), respectively. A mathematical model was used to estimate the effect of the support. The results showed that the mass transfer resistance of the support reduced the flux. The water flux corrected for the mass transfer resistance over the support was as high as 40 and 51 kg/(m2‧h) at 90 °C for CHA and FAU membranes, respectively. To the best of our knowledge, these are the highest reported water fluxes for desalination by zeolite membranes in a pervaporation process.

A novel conversion of Ti-bearing blast furnace slag into Ti-containing zeolites: Comparison study between FAU and MFI type zeolites

In this work, the synthesis of FAU and MFI type Ti-containing zeolites from Ti-bearing blast furnace slag was first achieved via a facile hydrothermal method. The synthesized zeolites were identified to be Ti-NaX and Ti-NaZSM-5 zeolites, with excellent specific surface area of 663.2 and 325.2 m2/g, respectively. Ti species in the Ti-NaX zeolite contained the framework Ti species and amorphous extraframework Ti species, while the Ti species in Ti-NaZSM-5 zeolite were in the form of the two species of above and another anatase TiO2. To investigate the potential application of the synthesized zeolites in photocatalysis field, an exploratory study was carried out by degradation of methyl orange under UV irradiation. As demonstrated, the Ti-NaZSM-5 zeolite showed higher photocatalytic performance and was more suitable to be the support of the TiO2 photocatalyst than the Ti-NaX zeolite. Innovative conversion of TBFS into Ti-containing zeolite materials does provide not only a novel and low-cost approach to waste management, but also a promising material candidate for catalytic oxidation and environmental purification.

Highlighting the Anti-Synergy between Adsorption and Diffusion in Cation-Exchanged Faujasite Zeolites.

Using configurational-bias Monte Carlo simulations of adsorption equilibrium and molecular dynamics simulations of guest diffusivities of CO2, CH4, N2, and O2 in FAU zeolites with varying amounts of extra-framework cations (Na+ or Li+), we demonstrate that adsorption and diffusion do not, in general, proceed hand-in-hand. Stronger adsorption often implies reduced mobility. The anti-synergy between adsorption and diffusion has consequences for the design and development of pressure-swing adsorption and membrane separation technologies for CO2 capture and N2/O2 separations.

Simulation guided prediction of zeolites for the sorption of selected anions from water: Machine learning predictors for enhanced loading

The development of highly efficient adsorbents, especially those that can harvest anions like CrO42−, AsO43−, NO3– and PO43−, is one of the principal challenges in the water treatment field. The current study utilized a screening process involving an initial selection of zeolites based on the pore-limiting diameter, followed by GCMC (Grand Canonical Monte Carlo) simulations to identify high-performing zeolites for anion removal. CLO, LTN, MWF, TSC, ITV, PAU, FAU and DFO zeolites are the best performing in terms of loading while several zeolites like ANA, DFT, BIK, SBN and JNT gave no loading at all. In addition, quantum chemical calculations revealed that after adsorption of the anions on the zeolite, there is charge transfer between the zeolite and the anion. The CLO cluster has a charge of 0.64 before adsorption. After adsorption, it attains a charge of −0.06, suggesting that the phosphate ion acts as an electron donor while the CLO cluster, as an electron acceptor. Finally, machine learning was employed to rank the importance of the various descriptors that have influence on the removal of anions in water. Largest overall cavity diameter, mass and accessible pore volume appeared to be the three most important descriptors, thus, tuning the sphere cavity and inter channel diameter as well as engineering the accessible volume of zeolite architectures are of utmost important toward harvesting the desired anions.

Effects of different alkali metal cations in FAU zeolites on the separation performance of CO2/N2O

• Novel idea of traditional zeolite sorbent for CO 2 /N 2 O adsorption separation. • Potassium ions in zeolite have obvious effect on CO 2 /N 2 O separation. • KX zeolite has the most excellent performance for CO 2 selectivity against N 2 O. • PSA simulations verify actual separation capacity. N 2 O and CO 2 coexist in the exhaust gas of adipic acid production, while their physical properties are extremely similar, making it a big challenge to separate CO 2 and N 2 O mixture. Here, CO 2 /N 2 O separation performance on Faujasite (FAU) zeolites with same structure, different Si/Al ratio (zeolite X and Y) and alkali metal cation (Li ＋ , Na ＋ , K ＋ ) are researched. With the increase of the alkali metal cation radius (from Li + to K + ), the difference between the adsorption capacity of CO 2 and N 2 O and ideal adsorbed solution theory (IAST) selectivity of CO 2 /N 2 O become more significant. Among the zeolite investigated, K-zeolites have bigger difference on CO 2 and N 2 O adsorption capacities and better IAST selectivity (KX: 4.35, KY: 2.15) than Li + and Na + exchanged zeolites (NaX: 2.29, LiX: 1.28, NaY: 1.58, LiY: 1.38) at 1 bar and 298 K, and with the increase of K + exchange degree, the selectivity to CO 2 increases. According to the breakthrough experiment, CO 2 /N 2 O mixture (50%/50%, v/v) can be separated by KX efficiently with shorter penetration time and relatively longer retention time than KY. Pressure swing adsorption (PSA) simulations further indicate that, by one step enrichment, pristine 50% N 2 O can be enriched to 80.83% with a recovery of 61.62% on KX.

Encapsulation and controlled release of isothiazolinones in zeolite NaY (FAU)

NaY zeolite, an ordered, large pore molecular sieve pertaining to the FAU zeolite structural group, was studied as a novel matrix for the efficient preparation of a supported isothiazolinone-based biocide, and the results were compared to those corresponding to mesoporous silicas. To analyze the possibility of reducing the biocide ecotoxicity by encapsulation, a commercial biocide used for latex preservation (CMIT/MIT) was incorporated in the NaY zeolite structure by using two different methodologies: equilibrium adsorption (Zeo/Bio sample) and impregnation by total wetting (Zeo/Impreg sample). In the corresponding release tests, despite the large difference in the initial biocide amount released, the shape of the curve is nearly the same for both methods. Microbiological tests against fungi and bacteria were performed. The obtained results were compared to those previously obtained using mesoporous ordered silica SBA-15 and mesoporous foam MCF matrices (mesoporous/biocide samples named SBA-15/Bio, SBA-15/Impreg and MCF/Bio and MCF/Impreg respectively). For the Staphylococcus aureus the results from agar well diffusion assay shows that the inhibition zone is about 64 mm for Zeo/Impreg and about 55 mm for Zeo/Bio. As regards all the other materials, the inhibition zone does not exceed 46 mm. In the case of Escherichia coli, Zeo/Bio and Zeo/Impreg have an inhibition zone of about 43 and 37 mm, respectively. No one of the other materials shows an inhibition zone larger than 30 mm. Zeo/Impreg showed a greater inhibition zone against fungi (47 mm versus Chaetomium globosum and 53 mm versus Alternaria alternata, respectively) than SBA-15 and MCF impregnated with biocide.

A theoretical investigation on the hydrodesulphurisation mechanism of hydrogenated thiophene over Cu–Mo-modified FAU zeolite

ABSTRACT We have theoretically investigated the hydrodesulphurisation (HDS) mechanism of hydrogenated thiophene over Cu–Mo-modified FAU zeolite using a two-layer ONIOM (our Own N-layered Integrated molecular Orbital and molecular Mechanics) study. The thiophene is hydrogenated to 2,3-dihydrothiophene (2,3-DHT), 2,5-dihydrothiophene (2,5-DHT) and tetrahydrothiophene (THT) due to moderate free energy barriers. Hydrogenolysis desulphurisation (HYD) and concerted direct desulphurisation (DDS) are discussed. Ring-opening, hydrogen transfer and C−S bond cleavage steps of thiophene derivatives are involved in the HYD process. The rate-determining steps are the hydrogen transfer step for 2,5-DHT and C−S bond cracking step for 2,3-DHT and THT. The concerted DDS pathway is probably more favourable than the HYD pathway in the desulphurisation of 2,5-DHT. The difference charge density (DCD) analysis reveals that for the ring-opening process, the electrons are migrated from the organic chain to the Cu–Mo catalytic centre. The reduced density gradient (RDG) plots indicate that both steric hindrance and a weak van der Waals (VDW) interaction exist between organic fragment and catalytic centre for all transition states (TSs). The localised orbital locator (LOL) maps suggest that there are strong covalent interactions and weak VDW interactions between the atoms in the forming chemical bonds.

High-Silica Layer-like Zeolites Y from Seeding-Free Synthesis and Their Catalytic Performance in Low-Density Polyethylene Cracking.

Layer-like FAU-type zeolite Y was synthesized by an organosilane-assisted low-temperature hydrothermal method and its catalytic activity was verified in the low-density polyethylene (LDPE) cracking process. The synthesis procedure of high-silica layer-like zeolite Y was based on organosilane as a growth modifier, and for the first time, the seeding step was successfully avoided. The X-ray diffraction and electron microscopy studies, scanning electron microscopy and transmission electron microscopy confirmed the formation of pure FAU structure and zeolite particles of plate-like morphology arranged in the manner of the skeleton of a cuboctahedron. The in situ Fourier transform infrared (FT-IR) spectroscopic studies, low-temperature nitrogen sorption, and electron microscopy results provided detailed information on the obtained layer-like zeolite Y. The acidic and textural properties of layer-like zeolites Y were faced with the catalytic activity and selectivity in the cracking of LDPE. The quantitative assessment of catalyst selectivity performed in FT-IR/GC–MS operando studies pointed out that LDPE cracking over the layer-like material yielded value-added C3–C4 gases and C5–C6 liquid fraction at the expense of C7+ fraction. The detailed analysis of coke residue on the catalyst was also performed by means of FT-IR spectroscopy, thermogravimetric analysis, and thermoprogrammed oxidation coupled with mass spectrometry for the detection of oxidation products. The acidic and textural properties gave a foundation for the catalytic performance and coking of catalysts.

The effect of the presence of a hydroxyl group on the vibration frequencies of NO and NH3 adsorbates on Cu-Zn bimetallic nanoparticles in ZSM-5 and FAU zeolite – a DFT study

The objective of this study was to propose a more promising catalyst for the deNOx process to effectively eliminate harmful nitrogen oxides from the environment. In the present study we considered bimetallic dimers of copper and zinc deposited in zeolites. The study was performed with a computer calculation using DFT based on ab initio method and a cluster model. Two zeolite catalysts, FAU and ZSM-5, were selected with an additional Cu-O-Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of adsorption of nitric oxide and ammonia in a different environment was selected. Two types of adsorption were proposed: with only a bridging oxygen of the dimer and with a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with the bimetallic dimer and the OH group behave differently than ZSM-5, regarding both NO and NH3 adsorption. A full vibrational analysis of the adsorbates was developed. The obtained anharmonic vibrations can be used to improve the interpretation of comprehensive experimental data of the deNOx process on bimetallic systems.

Theoretical Studies on the Mechanism of deNOx Process in Cu-Zn Bimetallic System-Comparison of FAU and MFI Zeolites.

In the present study we propose a more promising catalyst for the deNOx process to eliminate harmful nitrogen oxides from the environment. The study was performed with a computer calculation using density functional theory (DFT) based on an ab initio method. Two zeolite catalysts, FAU and MFI, were selected with additional Cu–O–Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of co-adsorption of nitric oxide and ammonia was selected, which became the initial configuration for the reaction mechanism. Two types of mechanisms were proposed: with hydroxyl groups on a bridged position of the dimer or a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with a bimetallic dimer and an OH group on the zinc atom was the most efficient configuration with a relatively low energy barrier. The real advantage of the Cu–Zn system over FAU and MFI in hydrothermal conditions has been demonstrated in comparison to a conventional Cu–Cu catalyst.

Competitive and sequence reactions of typical hydrocarbon molecules in diesel fraction hydrocracking - a theoretical study by DFT calculations.

The molecular structures of hydrocarbon molecules determine the competitive and sequence reactions in the diesel hydrocracking process. In this study, the hydrocracking reactions of typical hydrocarbons with various saturation degrees and molecular weights in diesel fractions synergistically catalyzed by the Ni–Mo–S nanocluster and Al–Si FAU zeolite are investigated. The results show that the two major rate-controlling steps in saturated hydrocarbon hydrocracking are dehydrogenation on the Ni–Mo–S active sites and the cracking of the C–C bonds on the FAU zeolite acid center. Moreover, the major rate-controlling step in cracking the cycloalkyl aromatic hydrocarbons is the protonation of the aromatic ring. Moreover, the aromatic hydrocarbons presented an apparent advantage in competitive adsorption on the Ni–Mo–S active sites, whereas hydrocarbons with higher molecular weights demonstrated a moderate adsorption advantage on both Ni–Mo–S active sites and FAU zeolite acid centers.

MFI, BEA and FAU zeolite scavenging role in neonicotinoids and radical species elimination.

Ecotoxicity caused by neonicotinoid pesticides is largely due to oxidative stress on non-target species. Due to the fact that reactive radical species reach the environment, materials intended for pesticide removal should be applicable for the simultaneous removal of reactive radicals, as well. This work uses the spectroscopic, adsorptive and antioxidant responses from MFI, FAU and BEA zeolites as descriptors of their potential environmental importance. Different network structures and Si/Al ratios were correlated with excellent zeolite adsorption properties, as over 200 mg g-1 of investigated neonicotinoids, acetamiprid and imidacloprid, was achieved in one cycle. Additionally, after two regeneration steps, over 450 mg g-1 adsorbed pesticides were retained, in three adsorption cycles. Overall the best results were detected for the FAU zeotype in both tested applications, insecticide adsorption and radical-scavenging performance, with and without insecticides present. The proposed mechanism for adsorption relies on kinetic investigation, isotherm modelling and spectroscopic post-adsorption analysis and targets zeolite hydroxyl/siloxane groups as active sites for insecticide adsorption via hydrogen bonding. Neat, well-defined zeolite structures enable their prospective application in ecotoxic species removal.

Facile synthesis of zeolites under an atmospheric reflux system

Traditionally zeolites are produced under long aging processes and high autogenous pressure reactions associated with a lot of safety concerns and explosion risks. Herein, a facile zeolite synthesis method under atmospheric pressure using a reflux system is reported. The zeolite gel crystallizes rapidly under the synthesis conditions of heating, stirring, and reflux in an oil bath. We have successfully synthesized LTA, FAU, MFI, and BEA zeolites. This technique not only eliminates the potential risks associated with pressure vessels but also greatly improves the synthesis rate and speeds up the production cycle. This synthesis strategy provides a new, safe and rapid way of synthesizing zeolites. • Safe synthesis of various zeolite by reflux system. • The synthesis of zeolite under atmospheric reflux system is faster than the conventional method. • Different synthesis methods of zeolite in reflux system are introduced in detail.

Ultra-Thin Zeolite Cha and Fau Membranes for Desalination by Pervaporation

Ultra-Thin Zeolite Cha and Fau Membranes for Desalination by Pervaporation

IR-Spectroscopic Study of Complex Formation of Nitrogen Oxides (NO, N2O) with Cationic Forms of Zeolites and the Reactivity of Adsorbed Species in CO and CH4 Oxidation.

The formation of complexes and disproportionation of nitrogen oxides (NO, N2O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N2O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν10–2 and the combination bands of the stretching vibrations with other vibrational modes for N2O complexes with cationic sites in zeolites (ν30–1 + ν10–1, ν10–1 + δ0–2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400–2600 cm−1 (the ν10–1 + δ0–2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N2O complex formed, presumably two-point adsorption of N2O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH4 on the samples with preliminarily adsorbed N2O at 20–180 °C does not result in any oxidation of these molecules. NO+ and N2O3 species formed by disproportionation of NO are capable of oxidizing CO and CH4 molecules to CO2, whereas NOx is reduced simultaneously to N2 or N2O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established.

Understanding the zeolites catalyzed isobutane alkylation based on their topology effects on the reactants adsorption

The easy deactivation of zeolites catalyzed isobutane alkylation, originated from the preferential adsorption of olefin against isobutane, limits their industrial applications. In this work, the adsorption properties of zeolites towards isobutane and 1-butene with different topologies and Si/Al ratios were investigated using CBMC simulations. Based on the calculated Henry coefficient and adsorption heat, the adsorption affinity decreases with the increase of Si/Al ratio in FAU-type zeolites, while for 1-butene the decrease is more obvious. The adsorption capacity of zeolites towards isobutane and 1-butene depends on the interaction between adsorbents and adsorbates at low pressures, while on the effective void volume of adsorbents at high pressures. A satisfactory relationship between the adsorption selectivity (SI/O) and catalytic stability of zeolites for isobutane alkylation was found. Compared to FAU and LTL zeolites with expansions in pores or channels, BEA-15 and MTW-39 zeolites exhibit a much higher SI/O and catalytic stability.

In situ crystallization of CHA / FAU zeolites on volcanic stone in the absence of organic agents

Japan has over 100 active volcanoes, which accounts for approximately 10% in the world. This paper discloses a novel way of utilizing volcanic stone. Microporous zeolites were crystallized on the macroporous volcanic stone by in situ crystallization method which is one-step soft hydrothermal treatment in NaOH solution with no additives. The volcanic stone has two roles in this method. One role is sources of SiO 2 , Al 2 O 3 , and alkali cations for crystallizing zeolites, and another role is a macroporous support of the zeolites. Each type of zeolite, CHA (0.38 nm pore) and FAU (0.74 nm pore), was mainly crystallized on the whole surface of the volcanic stone, which was controlled by adjusting concentration of NaOH solution. All the composite samples showed higher specific surface area than the raw volcanic stone. The highest value achieved in FAU zeolite sample was 439 m 2 /g which is as high as a commercial powdery zeolite. The adsorption abilities of the composite samples for ammonium ion measured by batch experiments were higher than the commercial powdery zeolite. • Zeolite-stone composites were prepared by in situ crystallization of volcanic stone. • Zeolites were precipitated without collapsing macroporous structure of the stone. • CHA-type zeolite was successfully crystallized in the absence of organic agents. • The highest surface area was 439 m 2 /g, as high as a commercial zeolite powder. • The samples showed higher adsorption abilities for NH 4 + than the commercial zeolite.

Inclusion of bidentate phosphine molecules in the supercage of FAU zeolite

Bidentate phosphines (Ph 2 P(CH 2 ) n PPh 2 ) with different alkyl chain lengths (n = 1–10) were included in the supercage (SC) of FAU-zeolite. Thermal treatment of the mixture of a bidentate phosphines and FAU-zeolite at 443 K resulted in the inclusion of the former into the SC, with up to 0.75 molecules per SC. The included molecules were strongly bound by FAU-zeolite, with desorption observed at higher temperatures compared to those of unloaded ones. The specific surface area of the FAU-zeolite decreased linearly with an increase in the number of phosphines included. This tendency was more emphasized in phosphines with n = 6–10 compared with those with n = 1–5. A characteristic shift in the C–C stretching band of the benzene ring was observed in the Fourier-transform infrared spectroscopy (FT-IR) spectrum, due to the strong interaction between bidentate phosphines and FAU-zeolite; the extent was more when using *BEA-loaded ones. Formation of the inclusion compounds between bidentate phosphines and FAU zeolites was observed with the molecular dynamics (MD) calculations. The bidentate phosphines included in the SC of the FAU-zeolite were reacted with PdCl 2 to form Pd complexes. The detailed analysis of the Pd complexes with Pd K-edge EXAFS revealed a characteristic decrease in the Pd–Cl bond distance with the use of complexes with n = 3 and 4, suggesting that the local structure around Pd was distorted through the interaction of the Pd complexes with the pores of the FAU-zeolite. The Pd complexes included in the SC were active for allylic alkylation between allyl methyl carbonate and ethyl acetoacetate. • Bidentate phosphines could be directly included in the supercage of FAU zeolite. • Formation of the inclusion compound was simulated by MD calculation. • Pd complexes with bidentate phosphines in SCs of FAU zeolite exhibited activity in the allylic alkylation.

A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility

AbstractA cooperative OSDA strategy is demonstrated, leading to novel high‐silica FAU zeolites with a large potential for disruptive acid catalysis. In bottom‐up synthesis, the symbiosis of choline ion (Ch+) and 15‐crown‐5 (CE) was evidenced, in a form of full occupation of the sodalite (sod) cages with the trans Ch+ conformer, induced by the CE presence. CE itself occupied the supercages along with additional gauche Ch+, but in synthesis without CE, no trans was found. The cooperation, and thus the fraction of trans Ch+, was closely related to the Si/Al ratio, a key measure for FAU stability and acidity. As such, a bottom‐up handle for lowering the Al‐content of FAU and tuning its acid site distribution is shown. A mechanistic study demonstrated that forming sod cages with trans Ch+ is key to the nucleation of high‐silica FAU zeolites. The materials showed superior performances to commercial FAU zeolites and those synthesized without cooperation, in the catalytic degradation of polyethylene.