Mixture Adsorption in Nanoporous Zeolite and at Its External Surface: In-Pore and Surface Selectivity

Using toluene, ethylene, and water as gas compounds with different representative molecular interactions, we perform atom-scale simulations for their mixtures to investigate the selectivity of the core nanoporosity and external surface in a prototypical zeolite. As expected, the overall behavior suggests that increasing the pressure of a given component promotes the desorption of the coadsorbing species. However, for water-toluene mixtures, we identify that the pseudohydrogen bonding between water and toluene leads to beneficial coadsorption as toluene adsorption in the low-pressure range promotes water adsorption. Moreover, when the zeolite is completely filled with water, toluene adsorption does not occur due to steric repulsion, and ethylene shows oversolubility as the amount of ethylene per water molecule is significantly larger than in bulk water. The underlying oversolubility mechanism is found to be due to localized ethylene adsorption in the density minima arising from the layering of water in nanoconfinement. Despite these specific effects, the relatively weak coadsorption effects in the zeolite nanoporosity, which are found to be reasonably captured using the ideal adsorbed solution theory, arise from the fact that adsorption of these gases having different molecular sizes occurs in distinct pore regions (channel type, channel intersection). Finally, in contrast to confinement in the nanoporosity, mixture adsorption at the external surface does not show coadsorption effects as it mostly follows the Henry regime. These results show that selectivity is mostly governed by the confinement effects as the external surface leads to a selectivity loss.

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

Controlled direct synthesis of single- to multiple-layer MWW zeolite

The minimized diffusion limitation and completely exposed strong acid sites of the ultrathin zeolites make it an industrially important catalyst especially for converting bulky molecules. However, the structure-controlled and large-scale synthesis of the material is still a challenge. In this work, the direct synthesis of the single-layer MWW zeolite was demonstrated by using hexamethyleneimine and amphiphilic organosilane as structure-directing agents. Characterization results confirmed the formation of the single-layer MWW zeolite with high crystallinity and excellent thermal/hydrothermal stability. The formation mechanism was rigorously revealed as the balanced rates between the nucleation/growth of the MWW nanocrystals and the incorporation of the organosilane into the MWW unit cell, which is further supported by the formation of MWW nanosheets with tunable thickness via simply changing synthesis conditions. The commercially available reagents, well-controlled structure and the high catalytic stability for the alkylation of benzene with 1-dodecene make it an industrially important catalyst.

Structure-Catalytic Properties Relationship in Friedel Crafts Alkylation Reaction for MCM-36-Type Zeolites Obtained by Isopropanol-Assisted Pillaring

MWW type zeolites are characterized by the presence of zeolitic layers of 2.5 nm thickness, containing 10-member ring sinusoidal channels inside and supercavities with 12-member ring openings located on their surfaces. Expansion and pillaring of layered zeolites increase the access to active sites and can enable or facilitate catalytic activity towards larger reactant molecules. This goal is explored in this work reporting the pillaring of layered zeolite MCM-56 with MWW topology by tetraethylorthosilicate (TEOS) treatment with the assistance of isopropanol, aimed at obtaining hierarchical micro-mesoporous systems. MCM-56 (Si/Al = 12) was synthesized with hexamethyleneimine as a structure-directing and aniline as a structure-promoting agent. Hierarchical porous systems were obtained using two different pillaring methods: (1) with TEOS only and (2) with TEOS mixed with isopropanol. The MWW framework was preserved during swelling/pillaring in both methods. Pillared zeolites obtained via alcohol-assisted pillaring possessed unique intermediate micro-mesopores with the size of about 2 nm. IR study revealed a decrease in the concentration of accessible acid centers upon pillaring. However, the fraction of acid sites on the external surface, accessible for adsorption of large molecules, increased by up to 90%. Catalytic activity was evaluated in the Friedel-Crafts alkylation of mesitylene with benzyl alcohol. Pillaring resulted in reduction of the acid site concentrations, but the materials retained high catalytic activity. Pillaring in the presence of alcohol produced increased turnover frequency values based on the concentrations of the external acid sites.

Detemplated and Pillared 2-Dimensional Zeolite ZSM-55 with Ferrierite Layer Topology as a Carrier for Drugs

The present studies were conducted to show the potential of 2D zeolites as effective and non-toxic carriers of drugs. Layered zeolites exhibit adjustable interlayer porosity which can be exploited for controlled drug delivery allowing detailed investigation of the drug release because the structure of the carrier is known exactly. This study was conducted with model drugs ciprofloxacin and piracetam, and ZSM-55 with ca 1 nm thick layers, in detemplated and pillared forms. The release profiles differed from the commercial, crystalline forms of drugs-the release rate increased for ciprofloxacin and decreased for piracetam. To understand the dissolution mechanisms the release data were fitted to Korsmeyer-Peppas equation, showing Fickian (for pillared) and anomalous (for detemplated sample) transport. FT-IR studies showed that strong interaction carrier-drug may be responsible for the modified, slowed down release of piracetam while better solubility and faster release of ciprofloxacin was attributed to formation of the protonated form resulting in weaker interaction with the zeolite than in the pure crystalline form. Two independent tests on L929 mice fibroblasts (ToxiLight and PrestoBlue) showed that ZSM-55, in moderate concentrations may be safely used as a carrier of drug molecules, not having negative effect on the cells viability or proliferation rate.

Encapsulation of Cu nanoparticles in nanovoids of plate-like silica sodalite through interlayer condensation of Cu2+ ion-exchanged layered silicate RUB-15

The interlayer condensation of layered silicates is a unique method for synthesizing zeolites and is effective for the introduction of metal species into platy zeolite frameworks. Layered silicate RUB-15 is a useful starting material because metal ions can be introduced between the layers and zeolite frameworks (all-silica SOD-type zeolite; silica sodalite) can be formed through interlayer condensation. In this study, Cu ions were intercalated into layered silicate RUB-15, and metal Cu nanoparticles were formed in the nanovoids of silica sodalite by a simple heat treatment in an inert atmosphere. Both interlayer condensation and the reduction of Cu2+ ions were confirmed by in situ XRD analysis performed during the heat treatment. The residual interlayer tetramethylammonium ions played two roles: the control of stacking sequence in the interlayer condensation and the reduction of Cu2+ ions. The formed Cu nanoparticles were stable in air atmosphere because of their confinement in the nanovoids of the sodalite frameworks.

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D-zeolite-based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.

Synthesis of Extra-Large-Pore Zeolite ECNU-9 with Intersecting 14*12-Ring Channels

Highly crystalline and (hydro)thermally stable zeolites with extra-large pores [≥14-ring (14-R)] are desirable as catalysts. A novel zeolite, ECNU-9, with an intersecting 14*12-R channel system was rationally designed and synthesized by a building block strategy, in which the interlayer expansion of a two-dimensional silicate structure was realized by combining organic amine assisted layer-stacking reorganization and subsequent silylation with a square-shaped single 4-ring (S4R) silane, 1,3,5,7-tetramethylcyclotetrasiloxane (TMCS). The PLS-3 precursor was disassembled into building blocks and then intercalated with flexible and removable organic amine pillars to offer enough interlayer spacing for accommodating TMCS molecules. The additionally introduced building blocks interconnected the neighboring layers to construct new 14-R and 12-R pores. ECNU-9 possesses a well-ordered structure with a novel topology. The corresponding Ti-ECNU-9, with tetrahedral Ti ions in the framework, showed superior catalytic performance in the selective epoxidation of bulky alkenes.

Toward a New Era of Designed Synthesis of Nanoporous Zeolitic Materials

Due to their nanoporous framework structures, zeolites have been widely used as catalysts, adsorbents, and ion exchangers in many industrial fields. Discovering zeolitic materials with new structures and desired functions is one of the most important tasks in the zeolite community. Traditional zeolite discovery relies primarily on low-efficiency trial-and-error processes. So far, many computational and experimental efforts have been devoted to the designed synthesis of zeolitic materials, representing a promising highway toward function-led discovery of nanoporous materials. In particular, the design of structure-directing agents, the design of target zeolites via structure enumeration, and the reorganization of disassembled building layers have led to the discovery of dozens of unprecedented zeolitic structures in the past 5 years. In this Perspective, we briefly discuss these advances and describe the research efforts that are needed in the coming era of function-led zeolite discovery.

Cutting Materials in Half: A Graph Theory Approach for Generating Crystal Surfaces and Its Prediction of 2D Zeolites

Scientific interest in two-dimensional (2D) materials, ranging from graphene and other single layer materials to atomically thin crystals, is quickly increasing for a large variety of technological applications. While in silico design approaches have made a large impact in the study of 3D crystals, algorithms designed to discover atomically thin 2D materials from their parent 3D materials are by comparison more sparse. We hypothesize that determining how to cut a 3D material in half (i.e., which Miller surface is formed) by severing a minimal number of bonds or a minimal amount of total bond energy per unit area can yield insight into preferred crystal faces. We answer this question by implementing a graph theory technique to mathematically formalize the enumeration of minimum cut surfaces of crystals. While the algorithm is generally applicable to different classes of materials, we focus on zeolitic materials due to their diverse structural topology and because 2D zeolites have promising catalytic and separation performance compared to their 3D counterparts. We report here a simple descriptor based only on structural information that predicts whether a zeolite is likely to be synthesizable in the 2D form and correctly identifies the expressed surface in known layered 2D zeolites. The discovery of this descriptor allows us to highlight other zeolites that may also be synthesized in the 2D form that have not been experimentally realized yet. Finally, our method is general since the mathematical formalism can be applied to find the minimum cut surfaces of other crystallographic materials such as metal-organic frameworks, covalent-organic frameworks, zeolitic-imidazolate frameworks, metal oxides, etc.

Hydrophobic Nanosized All-Silica Beta Zeolite: Efficient Synthesis and Adsorption Application

All-silica beta zeolite, synthesized by conventional hydroxide route, usually possesses small crystal size of a few hundred nanometers but poor hydrophobicity, whereas the fluoride-mediated one exhibits to be highly hydrophobic but microsized. To obtain nanosized all-silica beta zeolite with excellent hydrophobicity, an innovative and efficient hydrothermal route via interzeolite transformation for synthesizing all-silica beta zeolite is proposed in present study. With the assistance of beta seeds and tetraethylammonium hydroxide as the structure-directing agent, siliceous beta zeolite is well-crystallized at a high solid yield via dissolution-recrystallization of all-silica ITQ-1 crystals at an extremely low water content (H₂O/SiO₂ molar ratio of 1). The obtained all-silica beta crystals are composed of 30-70 nm nanoparticles and highly hydrophobic just next to siliceous beta-F zeolite synthesized by environmentally unfriendly fluoride route, which is derived from relatively small amounts of internal defect sites. Thus, this beta zeolite is superior to other pure silica beta zeolites in the adsorption of large-sized volatile organic compounds (VOCs), which is mainly attributed to its high total pore volume and specific surface area as well as excellent hydrophobicity.

Design of a highly active base catalyst through utilizing organic-solvent-treated layered silicate Hiroshima University Silicates

A layered-silicate base catalyst prepared by utilizing organic-solvent-treated HUS-7 exhibited remarkably high catalytic performance for the transesterification of triacetin.

External surface and pore mouth catalysis in hydrolysis of inulin over zeolites with different micropore topologies and mesoporosities

External surface and pore mouth catalysis for inulin hydrolysis over zeolite catalysts.

Recent advances in the textural characterization of hierarchically structured nanoporous materials

This review focuses on important aspects of applying physisorption for the pore structural characterization of hierarchical materials such as mesoporous zeolites.