Lamellar Zeolite Research Articles

Zeolitic Pickering Emulsifier with Intrinsic Amphiphilicity.

The formation of oil-in-water Pickering emulsions stabilized by lamellar zeolite MWW (International Zeolite Association, three-letters code) emulsifier without surface grafting is investigated. The crucial emulsification factors are the oligolayer morphology and amphiphilicity developed upon acidic treatment (NH4+ exchange/calcination, HNO3 treatment). In contrast with the readily available/abundant hydrophilic ≡Si-OH group in layer MWW, the lipophilicity generated by strong acid sites is another key to the success of emulsification. Hydrocarbon-strong acid site interaction is long known in petrochemistry and superacid research. However, to the best of our knowledge, this interaction was first introduced to gain lipophilicity in emulsion formation. Finally, the Pd-loaded acidic form of the MWW zeolite successfully stabilized the toluene/H2O emulsion system. The biphasic interfacial nitroarene hydrogenation demonstrated excellent catalytic performance. Overall, this work provided not only a new kind of intrinsic solid to emulsify the organic-aqueous biphase system but also a new mechanism to generate lipophilicity. Both are important for the applications and designs of Pickering emulsion materials.

Characterization and application of lamellar zeolite‐X prepared from kaolin

AbstractA simple and effective method was reported for the rapid synthesis of zeolite X from kaolin by adding a template agent. The results of X‐ray diffraction confirm the good crystallinity of the synthesized X‐zeolite with lamellar structure. Transmission electron microscopy images clearly demonstrate the lamellar structure of the synthesized X‐zeolite. The corresponding selective electron diffraction pattern suggests that the crystal structure of X‐type zeolite is octahedral. The co‐existence and uniform distribution of Si, Al, O, and Na in the layered structure of the synthesized X‐type zeolite are detected by element mapping. In addition, N2 adsorption–desorption measurement indicates that the specific surface area of the lamellar zeolite X is 153.4625 m2 g−1. The micropore surface area is 148.8374 m2 g−1, and the micropore volume is 0.073377 m2 g−1. After exploring the influence of different temperatures on the adsorption of carbon dioxide, the research shows that two‐dimensional zeolite X has the best adsorption capacity for carbon dioxide. The adsorption and separation performance of CO2/CH4 was investigated. The study showed that the adsorption and separation coefficient of two‐dimensional zeolite X was the highest.

Ex-situ catalytic fast pyrolysis of wood chips over lamellar MFI zeolite supported nickel catalyst

Lamellar MFI zeolite and lamellar MFI zeolite supported nickel were synthesized and examined for ex-situ catalytic upgrading of the vapors (without using any fluidized gases such as N2 and H2) resulted from fast pyrolysis of wood chips in comparison to its commercial MFI zeolite and its supported nickel counterparts. Pyrolysis tests were carried out using a catalytic augur reactor at atmospheric pressure, while pyrolysis unit was operating at 450 °C and upgrading unit at 420 °C, respectively. The introduction of nickel with a high dispersion over the zeolitic supports caused a significant increase in the products of aromatic compounds. Moreover, the addition of nickel to zeolite supports changed their acidity and decreased the total number of acid sites and the ratio of Brønsted to Lewis acid sites as determined by pyridine-FTIR spectroscopy. The use of lamellar zeolite catalysts increased the efficiency of catalytic cracking of pyrolysis vapors and their modification with nickel helped tuning the Lewis acidity to further increase catalytic cracking which resulted in a higher yield of the low molecular weight aromatics present in the bio-oil.

A theoretical study of the effect of exchange cations in surface of ZSM-5 lamellar zeolites

The electronic properties of various cationic forms of MFI type lamellar zeolites were studied using DFT calculations and compared with their bulk counterparts. In this study, Na+ and H+ cations were considered for the effect of charge deficit compensation on the surface of lamellar zeolites. The results show that lamellar zeolites in different cationic forms exhibit two distinct band gap widths, whose values are lower than those of their bulk counterparts and arise from the surface atoms. Furthermore, the results suggest that the Na+ cation behaves as a structure-directing agent on the surface, while H+ passivates the surface of the lamellar zeolites.

Local environment and catalytic property of External Lewis acid sites in hierarchical lamellar titanium Silicalite-1 zeolites

Abstract Hierarchical two-dimensional (2D) lamellar zeolites represent a young emerging field and a novel expression of the zeolite frameworks. Accompanied with synthesis and catalytic performance investigation, assessment on the local environment and catalytic behavior of acid sites in 2D zeolites are needed. Here, we described the local environment of Lewis acid sites and evaluated catalytic activities of external acid sites (i.e. sites on external surface and in mesopores) in 2D lamellar titanium silicalite-1 (TS-1) zeolites. For comparison purpose, four TS-1 zeolites, including 3D TS-1, multilamellar 2D TS-1 without pillarization and with pillarization by silica and silica/titania, respectively, were prepared. The local environment of Ti-sites, including coordination status of Ti-atom, speciation of hydroxyl (-OH) group that hints degree of confinement, acid site strength and accessibility, was collectively assessed by spectroscopic and organic base titration measurements. Kinetic studies of cyclooctene (C8H14) epoxidation with hydrogen peroxide (H2O2) discerned catalytic activity of external Ti-sites that decreased with increasing mesoporosity due to decrease in site confinement.

Cover Feature: A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds (Chem. Eur. J. 46/2020)

Cover Feature: A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds (Chem. Eur. J. 46/2020)

Assessment of coke deposits on lamellar metal-modified MFI zeolites in ethylene transformation to aromatic liquids

The effects of meso-/microporous structure and metal-additive (Ga or Zn) of lamellar MFI catalysts on the characteristics of coke deposits during ethylene-to-aromatic liquids conversion were investigated. The nature, composition, and location of coke deposits in spent lamellar catalysts were analyzed and compared to those on the microporous MFI counterparts, using FTIR, UV–Vis, GC–MS, and argon adsorption-desorption. The total amount of coke and the changes in coke nature during catalyst regeneration were studied by MS/FTIR combined with temperature programmed oxidation. The lamellar meso-/microporous structure of MFI reduces the coke quantity and the heavy coke fractions. The coke preferentially deposites on external surface of lamellar zeolite due to the lower diffusion limitation for bulky coke precursors. Metal-additive changes the catalyst acidity and decreases the coke formation rate, especially when zinc is used. Therefore, the coke formation on zeolite can be tuned by modulating the textural and acidity properties of the metal-modified catalyst.

Influences of metal-modification and lamellar zeolite structure on ethylene to liquid aromatics conversion reaction using MFI catalysts

The effects of meso-/microporous structure and metal-modification with gallium or zinc on catalytic performances of lamellar MFI zeolites in ethylene conversion reaction to liquid aromatics were investigated. TEM, XRD, Ar adsorption-desorption, UV-Visible spectroscopy, and H2-TPR measurements showed that the zeolite structure is a pivotal factor for controlling the type of metal dopant species forming on zeolite, their size, and their distribution. Adding metal dopants to zeolite structure decreased the Brønsted to Lewis (B/L) acid site ratio in the zeolites and improved their catalytic performance. As a result, metal-modified lamellar MFI zeolites showed higher liquid aromatics yield and selectivity for mono-benzene alkylated aromatics and lower coke formation rate compared to their microporous commercial MFI analogies. Zinc-loaded lamellar MFI had the most efficient catalytic performance among all studied catalysts. This phenomenon can be explained by higher accessibility of reactants to active sites and facilitated transport of products from lamellar structure of this zeolite and the low B/L acid site ratio of this catalyst provided by metal-modification, which is more suitable for ethylene aromatization. A bifunctional reaction mechanism has been proposed based on the analysis results of reaction product distributions that demonstrates the effect of both zeolite acid sites and metal sites in conversion of ethylene to liquid aromatics over MFI zeolite catalysts.

Mesopore differences between pillared lamellar MFI and MWW zeolites probed by atomic layer deposition of titania and consequences on photocatalysis

Abstract The pillared MWW (PMWW or MCM-36) and pillared MFI (PMFI) are two prominent representatives of meso-/microporous lamellar zeolites, which are made by pillaring of layered MCM-22(P) and multilamellar MFI precursors, respectively. They both consist of a 10-membered ring sinusoidal micropore channel within each zeolitic layer and mesopore voids created by pillars between two adjacent zeolitic layers. Although catalytic activities of PMWW and PMFI have been compared, identification of mesopore differences between these two pillared lamellar zeolites has not been attempted. In this work, we report the differences in mesopore characteristics between PMWW and PMFI zeolites probed by atomic layer deposition (ALD) of titania (ALD-TiO2) species and a combination of structural, textural, composition and catalytic property analyses of the samples before and after ALD treatment, respectively. The results suggest PMFI has cylindrical mesopores with uniform sizes from pore entrance to main body, while PMWW has ink-bottle mesopores with the neck size much smaller than pore body. The communication between micropore and mesopore in PMFI is direct, but no communication exists in PMWW zeolites. The ALD-TiO2 process considerably modified external surface composition of PMFI and PMWW zeolites, which consequently led to a new application of the pillared lamellar zeolite materials, i.e., photo-catalytically active meso-/microporous zeolites for environmental remedy reactions.

Synthesis of hierarchical lamellar MFI zeolites with sequential intergrowth influenced by synthetic gel composition

Abstract Hierarchical lamellar zeolites, comprised of both micro- and mesoporosity, afford high active site accessibility and mass transport in processing of bulky molecules. Here, we report the synthesis of hierarchical lamellar MFI zeolites with sequential intergrowth that is induced by composition variation in the standard recipe of 100SiO2/0.5Al2O3/3C22-6-6/18.5Na2O/4000H2O, where C22-6-6 stands for the diquaternary ammonium surfactant ([C22H45 N+(CH3)2 C6H12 N+(CH3)2 C6H13]Br−2) template. The influences of C22-6-6 concentration, alkalinity, and aluminum amount on the intergrowth of hierarchical lamellar MFI zeolites were investigated. The consequences of intergrowth on mesoporosity were analyzed. In all studied synthesis conditions except for very low alkalinity, hierarchical lamellar MFI zeolites were successfully crystallized. The increasing template concentration in the synthesis gel resulted in an increase in intergrowth and thus mesoporsotiy in the hierarchical MFI products. The increasing alkalinity led to an increase and then a decrease in mesoporosity in the hierarchical MFI products, which reflects the same trend in intergrowth in the hydrothermal synthesis process. The aluminum concentration, however, did not significantly affect the intergrowth and mesoporosity of the resultant hierarchical MFI zeolites. The sequential intergrowth achieved by simple variation in the synthesis composition for lamellar MFI zeolites resulted in higher structure hierarchy, mesoporosity, and acid site accessibility in one-step.

The construction of a series of hierarchical MWW-type zeolites and their catalytic performances for bulky aldol condensation

The construction of hierarchical pore systems from the post-synthesis modifications of lamellar zeolite catalysts have attracted wide interests to solve the diffusion limitations in the catalytic application of zeolite catalysts. Herein, the interlayer expanded MWW with different interlayer spacing were obtained, based on the post-synthesis modifications of a swollen multilamellar MWW precursor, in which the MWW layers were pillared by cetyltrimethylammonium bromide (CTAB) surfactant with 25 Å interlayer distance. The direct calcination and the post-synthesis modifications led to zeolite catalysts with more open pore structures (hierarchical, interlayer expanded and pillared), which were evidenced by a series of characterizations, such as PXRD, TEM, N2 adsorption-desorption etc. Moreover, the catalytic performances of the hierarchical MWW (H-MWW), interlayered expanded zeolite IEZ-MWW and Pillared-MWW catalysts were compared with 3D-MWW and ZSM-5 in the condensation of cyclohexanone with glycol or benzaldehyde with 1-pentanol. The catalysts prepared in this study show better catalytic activities than 3D-MWW and ZSM-5.

A Hierarchical MFI Zeolite with a Two-Dimensional Square Mesostructure.

A conceptual design and synthesis of ordered mesoporous zeolites is a challenging research subject in material science. Several seminal articles report that one-dimensional (1D) mesostructured lamellar zeolites are possibly directed by sheet-assembly of surfactants, which collapse after removal of intercalated surfactants. However, except for one example of two-dimensional (2D) hexagonal mesoporous zeolite, no other zeolites with ordered 2D or three-dimensional (3D) mesostructures have been reported. An ordered 2D mesoporous zeolite can be templated by a cylindrical assembly unit with specific interactions in the hydrophobic part. A template molecule with azobenzene in the hydrophobic tail and diquaternary ammonium in the hydrophilic head group directs hierarchical MFI zeolite with a 2D square mesostructure. The material has an elongated octahedral morphology, and quaternary, ordered, straight, square channels framed by MFI thin sheets expanded along the a-c planes and joined with 90° rotations. The structural matching between the cylindrical assembly unit and zeolite framework is crucial for mesostructure construction.

A Hierarchical MFI Zeolite with a Two‐Dimensional Square Mesostructure

AbstractA conceptual design and synthesis of ordered mesoporous zeolites is a challenging research subject in material science. Several seminal articles report that one‐dimensional (1D) mesostructured lamellar zeolites are possibly directed by sheet‐assembly of surfactants, which collapse after removal of intercalated surfactants. However, except for one example of two‐dimensional (2D) hexagonal mesoporous zeolite, no other zeolites with ordered 2D or three‐dimensional (3D) mesostructures have been reported. An ordered 2D mesoporous zeolite can be templated by a cylindrical assembly unit with specific interactions in the hydrophobic part. A template molecule with azobenzene in the hydrophobic tail and diquaternary ammonium in the hydrophilic head group directs hierarchical MFI zeolite with a 2D square mesostructure. The material has an elongated octahedral morphology, and quaternary, ordered, straight, square channels framed by MFI thin sheets expanded along the a–c planes and joined with 90° rotations. The structural matching between the cylindrical assembly unit and zeolite framework is crucial for mesostructure construction.

Synthesis of titanosilicate pillared MFI zeolite as an efficient photocatalyst

Adsorption assisted photocatalysis over pillared lamellar zeolite.

Recent Advances in the Synthesis and Application of Two‐Dimensional Zeolites

Two‐dimensional (2D) zeolites, originating from lamellar precursors, are a special kind of porous materials, in which crystalline zeolite nanolayers are weakly assembled in one particular direction. As there is no covalent‐bond between layers, the stacking sequences could be manipulated and possibly controlled to derive a family of zeolitic materials with structural diversity. The research on 2D zeolites arises from the primary casual discovery during traditional hydrothermal synthesis, which is followed by appropriate postsynthetic modifications to produce hierarchical lamellar zeolites. Recently, this area has experienced a remarkable evolution, which is highlighted by the rational synthesis of zeolite nanosheets by adopting a family of bifunctional surfactants and novel 3D zeolites through the “Assembly‐Disassembly‐Organization‐Reassembly” (ADOR) mechanism. Particularly, the direct construction of hierarchical lamellar zeolites with bifunctional surfactant is promising for industrial catalysis. Besides, an innovative top‐down method has demonstrated to be effective to produce novel types of 2D zeolites. Novel or even unfeasible zeolite topologies could be constructed by organizing and reassembling of the resulting layers. Here, the most attractive points achieved in the field of 2D zeolites are summarized, and the challenges and opportunities of zeolite chemistry associated with this type of porous materials are also proposed.

Self-Assembly of Cetyltrimethylammonium Bromide and Lamellar Zeolite Precursor for the Preparation of Hierarchical MWW Zeolite

Construction of hierarchical zeolite catalysts from lamellar zeolite precursor is challenging and promising for industrial catalysis. Although numerous efforts have been dedicated to control the organization of zeolite nanosheets by postsynthetic approaches or employing complex surfactants in hydrothermal synthesis, there is still no successful case that the hierarchical lamellar zeolite is hydrothermally synthesized by the self-assembly of the commercially available simple surfactant cetyltrimethylammonium bromide (CTAB) and inorganic zeolite precursor. In traditional syntheses, the self-assembly of simple surfactants and the growth of microporous framework are hardly compatible from both thermodynamic and kinetic viewpoints, preferring to cause phase separation. Herein, we approach for the first time the hydrothermal synthesis of a mesostructured multilamellar zeolite ECNU-7P, consisting of an alternative stacking of inorganic MWW zeolite nanosheets and organic CTAB layers with large interlayer spacing ...

Potentialities of the Modern Technology for the Production of Cracking Catalysts at the JSC Gazpromneft-Omsk Refinery

A series of cracking catalysts were developed by the Institute for Hydrocarbon Processing and are produced at the JSC Gazpromneft-Omsk Refinery. There are no world analogues for the unique technology for their production. Specifically, the catalysts are prepared using lamellar zeolite Y with crystals of 0,3–0,5 mm in size and a special matrix consisting of amorphous aluminosilicate, alumina and montmorillonite. At present the catalysts are loaded in four industrial setups with a total feed rate of ca. 7,000,000 t/y. Application of the new technological approaches makes it possible to produce the catalysts that provide the yields of gasoline fractions more than 60 wt.%.

Ru complexes of Hoveyda-Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions.

Hoveyda–Grubbs type catalysts with cationic tags on NHC ligands were linker-free immobilized on the surface of lamellar zeolitic supports (MCM-22, MCM-56, MCM-36) and on mesoporous molecular sieves SBA-15. The activity of prepared hybrid catalysts was tested in olefin metathesis reactions: the activity in ring-closing metathesis of citronellene and N,N-diallyltrifluoroacetamide decreased in the order of support MCM-22 ≈ MCM-56 > SBA-15 > MCM-36; the hybrid catalyst based on SBA-15 was found the most active in self-metathesis of methyl oleate. All catalysts were reusable and exhibited low Ru leaching (<1% of Ru content). XPS analysis revealed that during immobilization ion exchange between Hoveyda–Grubbs type catalyst and zeolitic support occurred in the case of Cl− counter anion; in contrast, PF6− counter anion underwent partial decomposition.

Spatial distribution and catalytic performance of metal–acid sites in Mo/MFI catalysts with tunable meso-/microporous lamellar zeolite structures

The lamellar MFI zeolite with tunable meso-/microporosity was prepared by a dual template synthesis method. Implications of the tunable meso-/microporosity on the spatial distribution and catalytic performance of metal–acid sites in Mo/lamellar MFI catalysts were studied. The number of free Brønsted acid sites increases linearly, accompanied by a linear decrease in Mo dispersion, with decreasing external surface areas in catalysts. The Mo–acid active sites coexisted on the external surface or mesopores of the catalysts linearly depends on the hierarchy factor, being the product of relative micropore volume and relative external surface area. The reaction rate and product selectivity of Mo/lamellar MFI in direct methane aromatization reactions are consistent with the trends of changes in zeolite porosities. These results imply that a balance between the meso- and microporosity in zeolite and the resultant active site distribution can be realized for desirable catalysis by simple one-step dual template synthesis of zeolites.

One-step dual template synthesis of hybrid lamellar-bulk MFI zeolite

A one-step dual template strategy was employed to achieve the facile synthesis of hybrid lamellar-bulk MFI (HLBM) zeolite, consisting of a lamellar zeolite structure on the surface of the bulk zeolite core. Tetrapropyl ammonium hydroxide (TPAOH) and diquarternary ammonium surfactant ([C22H45–N+(CH3)2–C6H12–N+(CH3)2–C6H13]Br2, C22-6-6) with a composition of 100SiO2/xC22-6-6/36TPAOH/4000H2O was used as the template in the HLBM zeolite synthesis. The influences of several parameters on the HLBM zeolite formation were investigated, including concentration of C22-6-6, hydrothermal synthesis time, and ageing temperature and time prior to hydrothermal crystallization. The sizes of lamellar and bulk domains of the HLBM zeolite and thus its meso- and micro-porosity can be modulated by simply tuning these parameters. A possible growth scheme of the HLBM zeolite is discussed. The ability to form hybrid zeolite particles with tunable meso-/micro-porosity is important to keep their potential application as broad as possible for specific zeolite structures. The dual template synthesis approach presented is potentially applicable to form other types of hybrid lamellar-bulk zeolite materials.