High-silica Zeolites Research Articles

Zeolite MFI adsorbent for recovery of butanol from ABE fermentation broths produced from an inexpensive black liquor-derived hydrolyzate

In this work, high-silica MFI zeolite adsorbent was evaluated for selective recovery of butanol from a real ABE (acetone, butanol, and ethanol) fermentation broth by batch adsorption measurements. The fermentation broth was produced using a hydrolyzate originating from Kraft black liquor, an internal stream in pulp mills, i.e., a low-cost substrate. The adsorbent was very selective towards butanol and butyric acid and became nearly saturated with a mixture of butanol and butyric acid with relative amounts of butanol and butyric acid depending on the pH. The presence of phenolic compounds in significant amounts in the fermentation broths, originating from the black liquor hydrolyzate, did not affect the adsorption of butanol and butyric acid.

Organic Guests within a Ferroelastic Host: The Case of High Silica Zeolite ZSM-5

The physical–chemical properties of guest molecules confined within a zeolite framework host are known to be strongly affected by the confinement effects exerted through noncovalent host–guest interactions. On the basis of synchrotron time-resolved powder diffraction measurements and the Landau theory of ferroelastic phase transitions, we provide in this work evidence for the strong coupling existing between the thermodynamic properties of organic molecules (toluene, 1,2-dichloroethane, methyl-tert-butyl-ether) adsorbed within the ZSM-5 zeolite and the lattice strain driving the monoclinic-to-orthorhombic (ferroelastic-to-paraelastic) phase transition which controls connectivity and diffusivity in the zeolite framework.

Influence of UV-Activation of Modified Zeolite Catalysts on Their Physicochemical and Catalytic Properties in Their Process of Getting High-Octane Gasoline Components

The influence of UV-irradiation by an XeCl excimer lamp on the physicochemical and catalytic properties of MFI-type high-silica zeolites modified by cobalt tungsto- and molybdobismuthates in the process of getting high-octane gosoline components is studied. It is show that the concentration of acidic centers can be increased by 76%; the arene yield, by 4-13 wt%; and the octane number of the products, by 2-3 points as compared with starting zeolite if cobalt tungstobismuthate heteropoly compound (1 wt%) is used as the modifier and the material is activated by UV-irradiation for 24 min. It is established that UV-irradiation of modified zeolites increases the concentration of acidic centers and decreases the adsorption capacity and specific surface area.

Insights into Adsorption of Chlorobenzene in High Silica MFI and FAU Zeolites Gained from Chromatographic and Diffractometric Techniques

In this work, the capability of two commercial high silica zeolites (HSZs), namely ZSM-5 and Y, for the removal of chlorobenzene (CB) from water was investigated by combining chromatographic and diffractometric techniques. The adsorption isotherms and kinetics of CB on ZSM-5 and Y zeolites were determined from batch tests. The adsorption kinetics were very fast; the time to reach equilibrium was less than 10 min. The equilibrium data of CB on the two HSZs showed dissimilarities that are particularly evident in the adsorption data concerning the low concentration range, where Y zeolite is characterized by low adsorption. On the contrary, at higher solution concentrations the adsorption capacity of Y is higher than that of ZSM-5. The crystalline structures of Y and ZSM-5 saturated with CB were investigated by X-ray diffraction (XRD) techniques. Rietveld refinement analyses of XRD data allowed for quantitative probing of the structural modifications of both zeolites after CB adsorption and provided insight into the preferred zeolite adsorption sites in both microporous materials. The refined framework–extraframework bond distances confirm that interactions between the selected organic contaminant and hydrophobic zeolites are mediated via co-adsorbed H2O. The occurrence of H2O–CB–framework oxygen oligomers explains variations in both the unit cell parameters and the shape of the channels, clearly confirming that water plays a very relevant role in controlling the diffusion and adsorption processes in hydrophobic zeolites.

Rapid preparation of high-silica CHA-type zeolite membranes and their separation properties

Abstract High-silica CHA-type zeolite membranes (HS-CHA membranes) have attracted considerable attention as zeolite membranes with high permeability, separation performance, and stability. However, long hydrothermal reaction times are required to form HS-CHA membranes. Therefore, in this study we investigated more rapid preparation methods to produce high performance HS-CHA membranes for practical applications. In our preparation process, FAU-type zeolite and N,N,N-trimethtyl-1-adamantammonium hydroxide were used as a raw material and structure-directing agent, respectively, through the secondary growth of seed crystals. As a result, the HS-CHA membranes could be prepared in a 5-h hydrothermal reaction. The permeation properties of the membranes were determined for pervaporation for either ethanol (EtOH), 2-propanol (IPA), or acetic acid (AcOH) solution containing water at 348 K. The permeation flux and separation factor of 80 wt% IPA solution with the use of the HS-CHA zeolite membrane with a Si/Al ratio of 11 were 20 kg m−2 h−1 and 1128, respectively. Furthermore, the gas separation performances of the HS-CHA membranes for binary mixtures of CO2 and CH4 were evaluated. For an equimolar mixture of the gases at 313 K, the CO2 permeance and the selectivity were 1.5 × 10−6 mol m−2 s−1 Pa−1 and 115, respectively.

Ozonation of aqueous phenol using high‐silica zeolite in an aerated mixing vessel

AbstractWe examined the degradation of aqueous phenol by ozonation in an aerated mixing vessel, which was combined with a fixed‐bed reactor packed with high‐silica zeolite (HSZ) pellets. Ozone‐containing oxygen gas was introduced as fine bubbles through a sparger placed in the aerated mixing vessel, whereas the aqueous phenol solution was circulated between the vessel and the reactor. Measurements of transient changes in the concentration of both phenol and total organic carbon in the treated solution revealed that the degradation of phenol or total organic carbon by ozonation was enhanced by the presence of HSZ because both phenol and ozone could adsorb on the hydrophobic micropores. As a result of quantitative analysis of the treated solution, it was found that catechol, hydroquinone, humic acid, and maleic acid were the possible reaction intermediates during ozonation of aqueous phenol employing HSZ.

Enhanced adsorption at ZnO nanoflakes@zeolite core shell interface: A study of changing adsorption dynamics

The present work describes the effect of surface modification of a high silica zeolite on removal of multiple ions [Pb(II), Fe(III), Cd(II)] and organics (Methylene blue, Aniline and p-nitrophenol) from contaminated water systems. Porous layer of ZnO nanoflakes (NFs) is grown on the surface of the zeolite in the form of a core-shell (CSPs) which alters the interface of the zeolite to convert the adsorption mechanism from slower chemisorption in zeolite to rapid physiochemisorption in CSPs as inferred from the comparative analysis of the adsorption dynamics. An inter-particle synergy encompassing ion exchange by zeolite and adsorption/photodegradation by the ZnO has been established by changed interfacial charge, enhanced surface area and increased porosity of the CSPs. Specificity of the developed CSPs for particular ions/organics and possible mechanism for enhanced adsorption of the CSPs has been discussed in detail. The specificity of adsorption follows the order of Pb (II) > Fe (III) > Cd (II) for heavy metal ions whereas for organics, the order of adsorption is methylene blue > p-nitrophenol > aniline. Results indicate that presence of ZnO nanoflakes as porous shell increases the equilibrium adsorption capacity of the CSPs to 74.661 mg/g in comparison to 45.96 mg/g of zeolite. The results of the specificity studies and significant increase in adsorption capacity prove that the altered interface leads to enhanced and rapid removal of toxic pollutants from water with highest specificity for Pb(II) and MB dye.

Thermal conversion of mechanically activated mixtures of aspen wood-zeolite catalysts in a supercritical ethanol

The mechanical activation of the mixture of aspen wood – high silica zeolite catalysts increases the wood thermal conversion in supercritical ethanol and rises the yield of liquid products. TH-HSZ-30 with Si/Al = .Zeolite catalysts allow to fractionate the mechanically activated wood in supercritical ethanol at 270 °C on solid lignocellulose and on soluble products from hemicelluloses, presented by furfural, 5-hydroxymethylfurfural, levulinic acid and ethyl esters. The elevated temperature (350 °C) decreases the yield of liquid products due to the intensification of secondary reactions of their transformation to gases and chars.The possible mechanism of wood catalytic conversion to bio-liquids in supercritical ethanol is discussed.

A Zeolite Family Nonjointly Built from the 1,3-Stellated Cubic Building Unit.

From a technological point of view, the synthesis of new high-silica zeolites is of prime importance owing to their high potential as industrial catalysts and catalyst supports. Two such materials have been synthesized which are made up of the 1,3-stellated cubic unit (hexahedral ([42 54 ]) bre unit) as a secondary building unit, with the aid of existing imidazolium-based structure-directing agents under "excess fluoride" conditions. One of them, denoted PST-21, is the first aluminosilicate zeolite consisting of 9-ring apertures solely; it displays exceptional activity towards steering the skeletal isomerization of 1-butene to isobutene and bridges the gap between small- and medium-pore structures. A series of hypothetical structures are also described that are nonjointly built from the bre unit; all of these structures are chemically feasible and will thus be helpful in designing the synthesis of novel zeolites containing 9-ring and/or 10-ring channels.

Supported Zeolite Beta Layers via an Organic Template-Free Preparation Route.

Layers of high silica zeolites, synthesized with an organic structure directing agent (OSDA) and grown onto porous support structures, frequently suffer from the thermal stress during the removal of OSDA via the calcination process. The different thermal expansion coefficients of the zeolite and the support material, especially when stainless steel is used as a support, causes enormous tension resulting in defect formation in the zeolite layer. However, the calcination is an easy procedure to decompose the OSDA in the pore system of the zeolite. Recently, methods to synthesize zeolite beta without the use of an organic structure directing agent have been described. In the present study, a seed-directed synthesis is used to prepare OSDA-free zeolite beta layers on stainless steel supports via an in situ preparation route. For the application as membrane, a porous stainless steel support has been chosen. The beta/stainless steel composites are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). To prove its possible application as a membrane, the beta/stainless steel composites were also tested by single gas permeances of H2, He, CO2, N2, and CH4.

Removal of crotamiton and its degradation intermediates from secondary effluent using TiO2-zeolite composites.

Crotamiton, a scabicide and antipruritic agent persistent during biological treatment processes, is frequently detected in secondary effluent. In this study, titanium dioxide (TiO2) and high-silica zeolite (HSZ-385) composites were synthesized and applied for the treatment of crotamiton in secondary effluent. Crotamiton was rapidly adsorbed by HSZ-385, and the adsorption performance of crotamiton in the secondary effluent was quite close to that in the test using ultrapure water. Even though the TiO2-zeolite composites showed lower adsorption rates than that of HSZ-385, similar crotamiton adsorption capacities were revealed using both test materials. The photocatalytic decomposition of crotamiton was significantly inhibited by the water matrix at low initial concentrations. The TiO2-zeolite composites rapidly adsorbed crotamiton from secondary effluent, and then the crotamiton was gradually decomposed under ultraviolet irradiation. Importantly, when using TiO2-zeolite composites, coexisting material in the secondary effluent did not markedly inhibit crotamiton removal at low initial crotamiton concentration. The behaviors of the main intermediates during treatment demonstrated that the main degradation intermediates of crotamiton were also captured by the composites.

Well-Defined Silanols in the Structure of the Calcined High-Silica Zeolite SSZ-70: New Understanding of a Successful Catalytic Material.

The structure of the calcined form of the high-silica zeolite SSZ-70 has been elucidated by combining synchrotron X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HRTEM), and two-dimensional (2D) dynamic nuclear polarization (DNP)-enhanced NMR techniques. The framework structure of SSZ-70 is a polytype of MWW and can be viewed as a disordered ABC-type stacking of MWW-layers. HRTEM and XRPD simulations show that the stacking sequence is almost random, with each layer being shifted by ±1/3 along the ⟨110⟩ direction with respect to the previous one. However, a small preponderance of ABAB stacking could be discerned. DNP-enhanced 2D 29Si{29Si} J-mediated NMR analyses of calcined Si-SSZ-70 at natural 29Si isotopic abundance (4.7%) establish the through-covalent-bond 29Si-O-29Si connectivities of distinct Si sites in the framework. The DNP-NMR results corroborate the presence of MWW layers and, more importantly, identify two distinct types of Q3 silanol species at the surfaces of the interlayer regions. In the first, an isolated silanol group protrudes into the interlayer space pointing toward the pocket in the adjacent layer. In the second, the surrounding topology is the same, but the isolated -SiOH group is missing, leaving a nest of three Si-O-H groups in place of the three Si-O-Si linkages. The analyses clarify the structure of this complicated material, including features that do not exhibit long-range order. With these insights, the novel catalytic behavior of SSZ-70 can be better understood and opportunities for enhancement recognized.

Recent trends in the synthesis of high-silica zeolites

ABSTRACTNovel zeolites continue to be synthesized using organic structure directing agents in combination with unconventional choices of inorganic conditions. The latter include synthesis in concentrated fluoride media, synthesis in concentrated hydroxide media, synthesis in the presence of germanium, and synthesis with high concentrations of boron. Post-synthetic treatments of germanosilicates with the ADOR method have resulted in fully intact zeolites that cannot be obtained through direct synthesis. Unusual compositions of known frameworks have been obtained through topotactic condensation of layered precursors. Coupled with the appropriate choice of inorganic conditions, the use of new SDA molecules has also produced materials with known frameworks but with amazingly small crystal dimensions that are less than 10 nm. The preparations of once “exotic” materials are now being performed with commercially available or easily prepared organic structure directing agents. In some instances methods have been found to prepare high-silica zeolites from seeded preparations in the absence of an organocation. Methods to target zeolite catalysts for a particular reaction have been realized by identifying structure directing agent molecules that are a mimic of the transition state of the reaction.

Enhanced Trace Carbon Dioxide Capture on Heteroatom-Substituted RHO Zeolites under Humid Conditions.

Boron and copper heteroatoms were successfully incorporated into the frameworks of high-silica RHO zeolite by adopting a bulky alkali-metal-crown ether (AMCE) complex as the template. These heteroatom-doped zeolites show both larger micropore surface areas and volumes than those of their aluminosilicate analogue. Proton-type RHO zeolites were then applied for the separation of CO2 /CH4 /N2 mixtures, as these zeolites have weaker electric fields and, thus, lower heats of adsorption. The adsorption results showed that a balance between working capacity and adsorption heat could be achieved for these heteroatom-doped zeolites. Ideal adsorbed solution theory predictions indicate that these zeolites should have high selectivities even for remarkably dilute sources of CO2 . Finally, the heteroatom-substituted zeolites, especially the boron-substituted one, could be thermally regenerated rapidly at 150 °C after full hydration and maintained high regenerability for up to 30 cycles; therefore, they are potential candidates for trace CO2 removal under humid conditions.

Experimental adsorption isotherms of CO2 and CH4 on STT zeolite: comparison with high- and pure-silica zeolites

Adsorption isotherms of CO2 and CH4 on a high-silica STT zeolite (Si/Al = 27), an odd zeolite which consists of 7- and 9-MR window openings, were measured over pressure range of 0–100 kPa at temperatures 298, 323 and 348 K. The isotherms follow typical Type-I according to the BDDT classification. Experimental isotherms data of CH4 and CO2 are well described by Langmuir-type isotherms. Calculation of isosteric heats of adsorption along with the isotherms types revealed that CH4 adsorption system is energetically homogeneous while that is heterogeneous for CO2 adsorption. Furthermore, comparison of STT adsorptive performance with high- and pure-silica zeolites led to development of a trade-off plot, i.e. CO2/CH4 selectivity against CO2 adsorption, by ideal adsorbed solution theory (IAST) calculations. The results revealed that Silicalite-1 has the lowest CO2/CH4 selectivity while SSZ-45 is the most selective adsorbent. Additionally, DD3R has the minimum CO2 adsorption amount whereas STT has the highest capacity. CO2/CH4 selectivity of STT is just ~ 12% smaller than that of SSZ-45 (13.30 against 15.12) but its CO2 adsorption is 63% greater than that of SSZ-45 (1.42 against 0.867 mol kg−1). Thus, STT zeolite is superior to the other high- and pure silica zeolite as it has simultaneously both high selectivity and capacity in CO2/CH4 separation.

Direct Synthesis of 2,5-Diformylfuran from Carbohydrates Using High-Silica MOR Zeolite-Supported Isolated Vanadium Species

Directly transforming carbohydrates into high value-added chemicals provides an economic and sustainable path for the utilization of the renewable biomass resource. Herein, we fabricated an efficient catalytic system for the straightforward conversion of various carbohydrates into 2,5-diformylfuran (DFF) by using vanadium oxide supported on high-silica mordenite (MOR) zeolites in the presence of hydrochloric acid. The synthesis of high-silica MOR zeolites was achieved in a template-free dense system featuring energy savings and environmental friendliness, delivering the SiO2/Al2O3 ratio up to 80. The conversion of fructose into DFF reached a high yield of 96.0% in a one-pot and one-step reaction by oxidation with atmospheric O2 (balloon), with facile recovery and good reusability of the catalyst. Good yields were also obtained in the direct synthesis of DFF from other carbohydrates including glucose, sucrose, inulin, raffinose, maltose, and starch. The high performance relied on the unique high-silica MOR...

SYNTHESIS OF In-CONTAINING HIGH-SILICA ZEOLITE OF ZSM-5 TYPE

High silicate zeolite ZSM-5 on the basis of SiO2–In2O3–NaOH with an organic structure forming agent tetrabutylammonium iodide (TBAI) was synthesized in the temperature range of T = 150–220°C, pH = 9-12, τ = 48-240 h. As initial components, silica gel MSKO containing 86% SiO2, tetrabutylammonium iodide (TBAI), chemically pure NaOH and metallic indium (In) were used which mixed by hydrothermal synthesis. At the end of the synthesis, the solid product was separated from the mother liquor, washed on the filter with distilled water from an excess of alkali and dried at 120 °C, calcined at 550 °C (16 h). The products of hydrothermal crystallization were determined by X-ray (RFA – on the device D2-Phaser "Bruker"), differential thermal (DTA- STA-449 F3 Jupiter NETZSCH), by X-ray diffraction (XRD of brand SRM-18) and infrared spectroscopy (IR on FTIR spectroscopy, Nicolefisio VSA) analysis methods. During the synthesis, it was experimentally established that at T = 200 °C; τ = 240 h; pH≈9-10 molar ratio of components 5.78SiO2∙0.058In2O3∙0.625Na2O∙0.11H2O∙0.95 ((C4H9) 4NJ) – MFI-type zeolite is crystallized. When comparing XRF data with literature data, they were referred to a type zeolite of ZSM-5 differing in high degree of crystallinity. The following chemical composition of the synthesized zeolite (wt.%) was established by the X-ray diffraction (SRM-18) method: SiO2 – 94.01; In2O3 – 4.92; Na2O – 1.06 corresponding to the formula 0.96Na2O:In2O3:88SiO2:10H2O.Forcitation:Samedov Kh.R., Mamedova U.A., Ragimov K.G., Jabbarova Z.A. Synthesis of In-containing high-silica zeolite of ZSM-5 type.Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 8. P. 84-87.

Identification of α-Fe in High-Silica Zeolites on the Basis of ab Initio Electronic Structure Calculations.

α-Fe is the precursor of the reactive FeIV═O core responsible for methane oxidation in Fe-containing zeolites. To get more insight into the nature and stability of α-Fe in different zeolites, the binding of Fe(II) at six-membered-ring cation exchange sites (6MR) in ZSM-5, zeolite beta, and ferrierite was investigated using DFT and multireference ab initio methods (CASSCF/CASPT2). CASPT2 ligand field (LF) excitation energies of all sites were compared with the experimental DR-UV-vis spectra reported by Snyder et al. From this comparison it is concluded that the 16000 cm-1 band of α-Fe, observed in all three zeolites, can uniquely be assigned to a high-spin square-planar (SP) Fe(II) located at a 6MR with an Al-Si-Si-Al sequence, where the Al atoms are positioned opposite in the ring and as close to each other as possible. The stability of such conformations is also confirmed by the binding energies obtained from DFT. The bands at 10000 cm-1 in the experimental spectra, assigned to spectator Fe(II), are attributed to six-coordinated trigonal-prismatic Fe(II) species, as calculated for the γ-site in ZSM-5. The entatic effect of the zeolite lattice on the stability of the SP sites was investigated by making use of the unconstrained Fe(II) model complex FeL2 (with L = [Al(OH)4]-). The SP conformer is approximately 2 kcal/mol more stable than the tetrahedral form, indicating that the SP coordination environment of α-Fe is not imposed by the zeolite lattice but rather electronically preferred by Fe(II) in the environment of four O ligands. A significant contribution to the stability of the SP conformer is provided by mixing of the doubly occupied 3dz2 orbital with the higher lying 4s.

Improved methanol-to-olefin reaction selectivity and catalyst life by CeO2 coating of ferrierite zeolite

The catalytic performance of the methanol-to-olefin (MTO) reaction over ferrierite zeolite was improved greatly by introduction of a CeO2 coating that selectively masked the acid sites on the external surface of the catalyst. In the absence of this coating, significant deterioration of the catalytic performance was observed owing to coke formation on the external surface and resultant blockage of the portals. Selective coating of CeO2 on the external surface was investigated using transmission electron microscopy, temperature-programmed desorption of NH3, N2 adsorption–desorption isotherms, and xenon adsorption measurements to reveal the structure–activity relationship. The resulting catalytic performance of CeO2-coated ferrierite zeolite in the MTO reaction was similar to that of MFI or high-silica CHA zeolite. The observed preferential formation of C4,= and C6,=, ∼90% free of aromatics was obtained because of the negligible deposition of heavy coke. This work shows that selective CeO2 coating on ferrierite zeolite was effective during catalyst regeneration and hydrothermal aging, leading to extended catalyst life and improved selectivity for catalytic applications.

Experimental Determination of the Molar Absorption Coefficient of n-Hexane Adsorbed on High-Silica Zeolites.

Determination of the molar absorption coefficients of the CH3 bending mode at ν˜ =1380 cm-1 (ϵ1380 ) of n-hexane adsorbed from the gas phase on two different dealuminated zeolites is derived by a combination of IR spectroscopy and microgravimetric analysis. High-silica zeolite Y (HSZ-Y) and zeolite ZSM-5 (with SiO2 /Al2 O3 ratios of 200 and 280, respectively) with different textural and surface features are selected to evaluate the effect of the pore structure and architecture on the value of ϵ1380 of the adsorbed n-hexane. Experimental data indicate that the molecule experiences a different adsorption environment inside zeolites; thus resulting in a significant change of the dipole moment and very different ϵ1380 values: (0.278±0.018) cm μmol-1 for HSZ-Y and (0.491±0.032) cm μmol-1 for ZSM-5. Experimental data are also supported by computational modeling, which confirms the effect of different matrices on the IR absorption intensity. This study reveals that the use of probe molecules for quantitative measurements of surface sites has to be judiciously adopted, especially if adsorption occurs in the restricted spaces of microporous materials.