A facile strategy to design zeolite L crystals with tunable morphology and surface architecture

Nonionic polymer and amino acid-assisted synthesis of ZSM-5 nanocrystals and their catalytic application in the alkylation of 2-methylnaphthalene

The synthesis of nanosized ZSM-5 zeolites with high crystallinity and suitable acidity is very significant for their great potential in various catalytic applications. Herein, a series of zeolite ZSM-5 crystals with different particle sizes and SiO2/Al2O3 ratios (10-30) were synthesized by a temperature-varying two-step crystallization method in a concentrated gel system containing L-lysine and/or polyvinylpyrrolidone (PVP) additives. By optimizing the addition amounts of the two additives, the crystal size of the ZSM-5 zeolite could be reduced to less than 100 nm. Meanwhile, relatively high crystallinity and framework Al incorporation rates could be achieved, resulting in the generation of high-quality ZSM-5 nanocrystals. The nanosized H-form ZSM-5 zeolite with a SiO2/Al2O3 ratio of 20 showed enhanced catalytic efficiency and stability for the alkylation of 2-methylnaphthalene (2-MN) with methanol to produce an important intermediate, 2,6-dimethylnaphthalene (2,6-DMN). A relatively high and steady yield of 2,6-DMN (above 7.2%) could be achieved during 20 h time-on-stream at 400 °C. The smaller crystal size, higher crystallinity and framework Al content could provide more accessible Brønsted acid sites in the 10-membered ring channel of the ZSM-5 nanocrystals, which are the main active sites responsible for the shape-selectivity of the targeted product of 2,6-DMN. As a result, the formation of other side products like 1-MN and poly-MN could be effectively inhibited, thus leading to an improved 2,6-DMN yield and coke resistance over the nanosized ZSM-5 catalyst.

Controlling Crystal Morphology of Anisotropic Zeolites with Elemental Composition

The morphology of zeolite crystals strongly affects their textural, catalytic, and mechanical attributes. However, controlling zeolite crystal morphology without using modifiers or structure-directing agents remains a challenging task because of our limited understanding of the relationships between zeolite crystal shape, crystallization mechanism, and composition of the starting synthesis mixture. In this study, we aimed at developing a general method for controlling the morphology of zeolites by assessing the impact of the Si/T molar ratio of the synthesis gel on the growth rate of zeolite crystals in various crystallographic directions and on the final crystal morphology of the UTL germanosilicate with a 2D system of intersecting 14- and 12-ring pores. Our results showed that flat UTL crystals progressively thicken with the Si/Ge molar ratio, demonstrating that Ge concentration controls the relative rate of crystal growth in the perpendicular direction to the pore system. The morphology of other zeolites and zeotypes with an anisotropic structure, including AFI (12R), IFR (12R), MWW (10-10R), and IWW (12-10-8R), can also be predicted based on their Si/T ratio, suggesting a systematic pattern across zeolite structures and in a wide range of zeolite framework elements. Combined, these findings introduce a facile and cost-efficient method for directly controlling crystal morphology of zeolites with anisotropic structures with a high potential for scale-up while providing further insights into the role of elemental composition in zeolite crystal growth.

Impact of a polymer modifier on directing the non-classical crystallization pathway of TS-1 zeolite: accelerating nucleation and enriching active sites

The crystallization process directly affects the physicochemical properties and active centers of zeolites; however, controllable tuning of the zeolite crystallization process remains a challenge. Herein, we utilized a polymer (polyacrylamide, PAM) to control the precursor structure evolution of TS-1 zeolite through a two-step crystallization process, so that the crystallization path was switched from a classical to a non-classical mechanism, which greatly accelerated nucleation and enriched active Ti sites. The TS-1 crystallization process was investigated by means of various advanced characterization techniques. It was found that specific interactions between PAM and Si/Ti species promoted the assembly of colloidal precursors containing ordered structural fragments and stabilized Ti species in the precursors, leading to a 1.5-fold shortened crystallization time and enriched Ti content in TS-1 (Si/Ti = 29). The PAM-regulated TS-1 zeolite exhibited enhanced catalytic performance in oxidative reactions compared to conventional samples.

Synthesis of Microporous Aluminosilicate by Direct Thermal Activation of Phenyl-Substituted Single-Source Aluminosilicate Molecular Precursors

The construction of aluminosilicates from versatile molecular precursors (MPs) represents a promising alternative strategy to conventional processes based on monomeric molecular or polymeric Al and Si sources. However, the use of MPs often suffers from drawbacks such as the decomposition of the core structures in the presence of solvents, acids, or bases. In this work, we demonstrate a simple thermal synthesis of porous aluminosilicates from single-source spiro-7-type MPs that consist of a tetrahedral Al atom and six Si atoms functionalized with 12 phenyl (Ph) groups, (C⁺)[Al{Ph₂Si(OSiPh₂O)₂}₂]^- (C⁺[AlSi₆]^-; C⁺ = pyridinium cation (PyH⁺), Na⁺, K⁺, Rb⁺, or Cs⁺), without using a solvent or activator. Microporous aluminosilicates synthesized via the thermal treatment of C⁺[AlSi₆]^- under a 79% N₂ + 21% O₂ atmosphere exhibited extremely low carbon contents (0.10-1.28%), together with Si/Al ratios of 3.9-6.7 ± 0.2 and surface areas of 103.1-246.3 m²/g. The solid-state ²⁷Al and ²⁹Si MAS NMR spectra suggest that the obtained aluminosilicates with alkali cations retain a tetrahedral Al site derived from the spiro-7-type core structure. After a proton-exchange reaction, the aluminosilicates showed almost 1.5 times higher reactivity in the catalytic ring-opening of styrene oxide than the aluminosilicate before proton exchange due to the catalytically active OH site being predominantly bridged by tetrahedral Al and Si atoms. These results suggest that the present MP strategy is a promising method for the introduction of key structures into active inorganic materials.

Nitrogen- and Halogen-Free Multifunctional Polymer-Directed Fabrication of Aluminum-Rich Hierarchical MFI Zeolites

Aluminum-rich hierarchical MFI-type zeolites with high acidic-site density exhibit excellent activity and selectivity in bulky molecule-involved reactions. However, it is challenging to develop a facile and environmentally benign method for fabricating them. Herein, we employ a polymer that does not contain nitrogen and halogen elements to successfully synthesize aluminum-rich hierarchical ZSM-5 zeolite with a Si/Al ratio of 8 and a significant number of mesopores comprised of oriented-assembled nanocrystals. It is demonstrated that the nitrogen- and halogen-free polymer is instrumental in the formation of the ZSM-5 zeolite by serving as a template for constructing the hierarchical micro/mesoporous structure. Moreover, this polymer also acts as a crystal growth modifier to form a single-crystalline zeolite. Notably, the resultant zeolite shows a better catalytic performance in converting waste plastic into hydrocarbons than a commercial one. Our work enables the synthesis of high-quality hierarchical zeolites without requiring quaternary ammonium templates.

Two-Step Dry Gel Method Produces MgAPO-11 with Low Aspect Ratio and Improved Catalytic Performance in the Conversion of Methanol to Hydrocarbons

In this article, the synthesis, characterization and catalytic performance of three MgAPO-11 catalysts with distinct crystal morphologies (sunflower, ball and candy) are presented. Among the three samples, the candy-like MgAPO-11-C, with high crystallinity and uniform particle size (of about 1 µm), was synthesized for the first time by using a unique two-step dry gel method. Despite the similar acid strength of the three samples, the different and distinct morphologies of the catalysts resulted in very different methanol-to-hydrocarbons (MTH) performances. In particular, the candy-like MgAPO-11-C presented the best MTH performance with the highest total conversion capacity (4.4 gMeOH·gcatalyst−1 h−1) and the best selectivity to C5+ aliphatics (64%).

Facile Synthesis of Nanosheet-Stacked Hierarchical ZSM-5 Zeolite for Efficient Catalytic Cracking of n-Octane to Produce Light Olefins

The development of an effective strategy for synthesizing two-dimensional MFI zeolites has attracted more and more attention. Herein, nanosheet-stacked hierarchical ZSM-5 zeolite was obtained by a seed-assisted hydrothermal synthesis route using a small amount of [C18H37-N+(CH3)2-C6H12-N+(CH3)2-C6H12]Br2 (C18-6-6Br2) as a zeolite structure-directing agent and triethylamine (TEA) as a zeolite growth modifier. By varying the molar ratio of C18-6-6Br2/TEA from 2.5/0 to 2.5/40, the morphologies and textural properties of the resultant HZ5-2.5/x catalysts were finely modulated. By increasing x from 5 to 40, the morphology of the HZ5-2.5/x changed from unilamellar assembly with narrow a–c plane to intertwined nanosheets with wide a–c plane and multilamellar nanosheets with house-of-cards morphology. The thickness of these nanosheets was almost 8–10 nm. In addition, selectivity to light olefins reached 70.7% for the HZ5-2.5/10 catalyst, which was 6.6% higher than that for CZSM-5 (64.1%). Furthermore, the MFI zeolite nanosheets exhibited better anticoking stability within the 60 h reaction time compared to conventional ZSM-5 zeolite, which could be attributed to the short diffusion path and hierarchical porosity. This work will provide valuable insights into the rational design of novel zeolite catalysts for the efficient cracking of hydrocarbons.

Crystallization of zeolite Beta in the presence of an anionic surfactant AESA

Organic molecules are widely used as structure directing agents, mesopore generating agents or zeolite growth modifiers in the synthesis of various zeolites. However, the organic molecules used in zeolite synthesis...

Mesoporogen-free synthesis of single-crystalline hierarchical beta zeolites for efficient catalytic reactions

Single-crystalline hierarchical Beta zeolites were synthesized by the l-lysine-assisted kinetic regulation method, exhibiting improved catalytic performance in both gas- and liquid-phase reactions.

Mesocrystal morphology regulation by "alkali metals ion switch": Re-examining zeolite nonclassical crystallization in seed-induced process

HYPOTHESIS

It is a Holy Grail to realize the goal-oriented synthesis of zeotype crystals via direct thermodynamic/kinetic control of crystallization in the simplest inorganic system. Especially, the most commonly used counter cations (i.e., Na⁺ and K⁺) are in turn believed to play merely the role of balancing charges and stabilizing frameworks, which make the simple ion-based morphology/porosity control remain big challenges.

EXPERIMENTS

We re-examined the role of Na⁺ and K⁺ to fine-tune the classical/nonclassical crystallization process in a seed-induced system with the simplest composition (Si/Al sources, inorganic alkali, and H₂O), and proposed an "ion switch" strategy. By analyzing the multiple growth curves, tracking the precursor evolution, and observing epitaxial crystallization behavior, a distinctive "ion switch"-worked nonclassical mechanism was uncovered.

FINDINGS

By the "ion switch" strategy, ZSM-5 mesocrystals were fine-regulated with diverse architecture from single crystal to nanocrystallite assembly and intracrystal mesopore-enriched crystal. Such simple ions-controlled crystallization was achieved through microstructure heterogeneity of zeolitic building-blocks triggered by different counterions and their corresponding assembly behavior from oriented attachment to random deposition. Furthermore, this protocol can be extended to a wider H₂O/SiO₂ range, mixed Na⁺/K⁺ systems, and other alkali metal ions from Li⁺ to Cs⁺, and ZSM-5 mesocrystals with extended morphologies can be obtained.

Factors controlling the molecular modification of one-dimensional zeolites

Interactions between organic molecules and inorganic materials are ubiquitous in many applications and often play significant roles in directing pathways of crystallization. It is frequently debated whether kinetics or thermodynamics plays a more prominent role in the ability of molecular modifiers to impact crystal nucleation and growth processes. In the case of nanoporous zeolites, approaches in rational design often capitalize on the ability of organics, used as either modifiers or structure-directing agents, to markedly impact the physicochemical properties of zeolites. It has been demonstrated for multiple topologies that modifier-zeolite interactions can alter crystal size and morphology, yet few studies have distinguished the roles of thermodynamics and kinetics. We use a combination of calorimetry and molecular modeling to estimate the binding energies of organics on zeolite surfaces and correlate these results with synthetic trends in crystal morphology. Our findings reveal unexpectedly small energies of interaction for a range of modifiers with two zeolite structures, indicating the effect of organics on zeolite crystal surface free energy is minor and kinetic factors most likely govern growth modification.

Direct Preparation of *MRE Zeolites with Ultralarge Mesoporosity: Strategy and Working Mechanism

Introduction of mesopore is critical for applications where mass-transport limitations within microporous networks, especially for zeolite with one-dimensional microporous network, hinder their performance. Generally, the creation of mesopore in zeolite through a direct synthesis route is strongly dependent on complex and expensive organic molecules, which limits their commercial application. Here, we successfully developed a facile synthesis route for preparing ZSM-48 zeolite (*MRE topology) with ultralarge mesoporosity in which typical 1,6-hexylenediamine worked as an organic structure-directing agent, innovatively assisted by a simple crystal growth modifier (tetraethylammonium bromide, TEABr). The working mechanism of TEABr during crystallization was revealed and proposed on the basis of TEM, thermal gravimetric mass spectrum, and ¹³C cross-polarization magic angle spinning NMR characterization results. In the process, TEA⁺ ions preferentially interacted with the solid during the induction period, which effectively suppressed the aggregation of ZSM-48 primary nanorods. As a result, ultralarge mesoporosity of 0.97 cm³·g^-1 was constructed through the stacking of the nanorods. Interestingly, TEA⁺ ions only took part in the crystallization process and did not occlude in the pores of the final zeolites indicating its potential in recyclability. Moreover, similar synthesis strategy could be applied for the preparation of hierarchical ferrierite zeolites, implying the universality of this strategy. Compared with a conventional sample, ZSM-48 zeolite with ultralarge mesoporosity showed superior catalytic stability in the m-xylene isomerization reaction due to its significantly enhanced diffusion and mass transfer capability, which will greatly promote the practical application of ZSM-48 zeolite.

A Comparative Analysis of In Vitro Toxicity of Synthetic Zeolites on IMR-90 Human Lung Fibroblast Cells

Broad industrial application of zeolites increases the opportunity of inhalation. However, the potential impact of different types and compositions of zeolite on cytotoxicity is still unknown. Four types of synthetic zeolites have been prepared for assessing the effect on lung fibroblast: two zeolite L (LTL-R and LTL-D), ZSM-5 (MFI-S), and faujasite (FAU-S). The cytotoxicity of zeolites on human lung fibroblast (IMR-90) was assessed using WST1 cell proliferation assay, mitochondrial function, membrane leakage of lactate dehydrogenase, reduced glutathione levels, and mitochondrial membrane potential were assessed under control. Intracellular changes were examined using transmission electron microscopy (TEM). Toxicity-related gene expressions were evaluated by PCR array. The result showed significantly higher toxicity in IMR-90 cells with FAU-S than LTL-R, LTL-D and MFI-S exposure. TEM showed FAU-S, spheroidal zeolite with a low Si/Al ratio, was readily internalized forming numerous phagosomes in IMR-90 cells, while the largest and disc-shaped zeolites showed the lowest toxicity and were located in submembranous phagosomes in IMR-90 cells. Differential expression of TNF related genes was detected using PCR arrays and confirmed using qRT-PCR analysis of selected genes. Collectively, the exposure of different zeolites shows different toxicity on IMR-90 cells.

Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio

Zeolite crystals offering a short diffusion pathway through the pore network are highly desired for a number of catalytic and molecule separation applications. Herein, we develop a simple synthetic strategy toward reducing the thickness along the b-axis of MFI-type crystals, thus providing a short diffusion path along the straight channel. Our approach combines preliminary aging and a fluoride-assisted low-temperature crystallization. The synthesized MFI crystals are in the micrometer-size range along the a- and c-axis, while the thickness along the b-axis is a few tens of nanometers. The synthesis parameters controlling the formation of platelike zeolite are studied, and the factors controlling the zeolite growth are identified. The synthesis strategy works equally well with all-silica MFI (silicalite-1) and its Al- and Ga-containing derivatives. The catalytic activity of platelike ZSM-5 in the methanol-to-hydrocarbons (MTH) reaction is compared with a commercial nanosized ZSM-5 sample, as the platelike ZSM-5 exhibits a substantially extended lifetime. The synthesis of platelike MFI crystals is successfully scaled up to a kilogram scale.

Controlling the Morphology and Titanium Coordination States of TS-1 Zeolites by Crystal Growth Modifier

Developing an effective strategy to synthesize perfect titanosilicate TS-1 zeolite crystals with desirable morphologies, enriched isolated framework Ti species, and thus enhanced catalytic oxidation properties is a pervasive challenge in zeolite crystal engineering. We here used an amino acid l-carnitine as a crystal growth modifier and ethanol as a cosolvent to regulate the morphologies and the Ti coordination states of TS-1 zeolites. During the hydrothermal crystallization process, the introduced l-carnitine can not only tailor the anisotropic growth rates of zeolite crystals but also induce the formation of uniformly distributed framework Ti species through building a suitable chemical interaction with the Ti precursor species. Condition optimizations could afford the generation of perfect hexagonal plate TS-1 crystals and elongated platelet TS-1 crystals enriched in tetrahedral framework Ti sites (TiO₄) or mononuclear octahedrally coordinated Ti species (TiO₆). Both samples showed significant improvement in catalytic activity for the H₂O₂-mediated epoxidation of alkenes. In particular, the elongated platelet TS-1 enriched in "TiO₆" species afforded the highest activity in 1-hexene epoxidation, with a turnover frequency (TOF) of up to 131 h^-1, which is approximately twice as high as that of the conventional TS-1 zeolite (TOF: 65 h^-1) and even higher than those of the literature-reported TiO₆-containting TS-1 catalysts derived from the hydrothermal post-treatment of TS-1 zeolites. This work demonstrates that the morphologies and the titanium coordination states of TS-1 zeolites can be effectively tuned by directly introducing suitable crystal growth modifiers, thus providing new opportunities for developing highly efficient titanosilicate zeolite catalysts for important catalytic applications.

Efficient recovery of Cu(II) by LTA-zeolites with hierarchical pores and their resource utilization in electrochemical denitrification: Environmentally friendly design and reutilization of waste in water

Water pollution seriously endangers human health and the environment. Here we prepared and tested mesoporous LTA zeolites for the adsorption of Cu(II) from aqueous media and the captured copper was further used for electrochemical nitrate reduction. The prepared hierarchically porous LTA exhibited a high capacity (341.5 mg g^-1) for Cu(II) adsorption, following the pseudo-second-order kinetic and Freundlich adsorption isotherm models well. The Cu-LTA sample was characterised by various analytical methods, and Cu(I) species were identified as the active sites for nitrate electrochemical reduction. Based on the spectral characterization and reducibility, strong metal-support interaction was found between copper and LTA, which is beneficial to the dispersion of active sites and their contacts with nitrates. In total, 10.1 g-N-NO₃ g^-1-Cu was reduced over the Cu-LTA-modified cathode in a three-electrode system with high N₂ selectivity (92.1 %). Compared to purely microporous zeolites, mesoporous LTA has a higher capacity for Cu(II) removal and nitrate reduction. The mesoporous structure allows easy access to the inner active sites with low diffusion resistance. The low Tafel slope and high current density confirm the high activity of the mesoporous Cu-LTA, making it a promising and efficient material for the removal and reuse of heavy metal ions.

Elucidating the restructuring-induced highly active bimetallic Pt–Co/KL catalyst for the aromatization of n-heptane

The restructured bimetallic Pt–Co/KL catalyst promotes the aromatization of n-heptane.

Strategies to control zeolite particle morphology

Methods to synthesize zeolites with different crystal habits and assemble zeolite crystals into specific structures are reviewed for the rational design of zeolite particle morphologies.

Crystal Engineering for Catalysis

Crystal engineering relies upon the ability to predictively control intermolecular interactions during the assembly of crystalline materials in a manner that leads to a desired (and predetermined) set of properties. Economics, scalability, and ease of design must be leveraged with techniques that manipulate the thermodynamics and kinetics of crystal nucleation and growth. It is often challenging to exact simultaneous control over multiple physicochemical properties, such as crystal size, habit, chirality, polymorph, and composition. Engineered materials often rely upon postsynthesis (top-down) processes to introduce properties that would otherwise be challenging to attain through direct (bottom-up) approaches. We discuss the application of crystal engineering to heterogeneous catalysts with a focus on four general themes: ( a) tailored nanocrystal size, ( b) controlled environments surrounding active sites, ( c) tuned morphology with well-defined facets, and ( d) hierarchical materials with disparate pore size and active site distributions. We focus on nonporous materials, including metals and metal oxides, and two classes of porous materials: zeolites and metal organic frameworks. We review novel synthesis methods involving synergistic experimental and computational design approaches, the challenges facing catalyst development, and opportunities for future advancement in crystal engineering.

Manipulating the mesostructure of silicoaluminophosphate SAPO-11 via tumbling-assisted, oriented assembly crystallization: a pathway to enhance selectivity in hydroisomerization

A house-of-cards architecture of silicoaluminophosphate was fabricated to enhance selectivity for hydroisomerization.

New insights into the di-n-propylamine (DPA) molecule as an organic structural directing agent (OSDA) in the crystallization of AlPO4-11 molecular sieve

Di-n-propylamine (DPA) molecules induce the transformation from 4/6-MR chains to a 2D layered structure and then to 3D crystals of AlPO₄-11 molecular sieves.

Synthesis of nano-sized LTL zeolite by addition of a Ba precursor with superior n-octane aromatization performance

Nano-sized LTL zeolites obtained by the Ba-assisted method show improved catalytic performance in n-octane aromatization reaction.

Nanosized MCM-22 zeolite using simple non-surfactant organic growth modifiers: synthesis and catalytic applications

Non surfactant cyclic alkylammonium can selectively decrease the rate of crystal growth along the x–y crystal axes during the synthesis of MWW zeolite.

Photoactive Nanomaterials Inspired by Nature: LTL Zeolite Doped with Laser Dyes as Artificial Light Harvesting Systems

The herein reported work describes the development of hierarchically-organized fluorescent nanomaterials inspired by plant antenna systems. These hybrid materials are based on nanostructured zeolitic materials (LTL zeolite) doped with laser dyes, which implies a synergism between organic and inorganic moieties. The non-interconnected channeled structure and pore dimensions (7.1 Å) of the inorganic host are ideal to order and align the allocated fluorophores inside, inferring also high thermal and chemical stability. These artificial antennae harvest a broad range of chromatic radiation and convert it into predominant red-edge or alternatively white-light emission, just choosing the right dye combination and concentration ratio to modulate the efficiency of the ongoing energy transfer hops. A further degree of organization can be achieved by functionalizing the channel entrances of LTL zeolite with specific tailor-made (stopcock) molecules via a covalent linkage. These molecules plug the channels to avoid the leakage of the guest molecules absorbed inside, as well as connect the inner space of the zeolite with the outside thanks to energy transfer processes, making the coupling of the material with external devices easier.

Controllable deposition of Pt nanoparticles into a KL zeolite by atomic layer deposition for highly efficient reforming of n-heptane to aromatics

Small-sized Pt particles inside KL zeolite channels are supposed to facilitate the dehydrogenation and cyclization of n-heptane.

Tuning Zeolite Precursor Interactions by Switching the Valence of Polyamine Modifiers

Nonclassical mechanisms of crystal growth often involve the formation of amorphous precursors that play a direct role in what is generally referred to as crystallization by particle attachment (or CPA). One of the most studied CPA systems in the literature is zeolite MFI, which is a microporous crystal with siliceous (silicalite-1) and aluminosilicate (ZSM-5) isostructures. The self-assembly, microstructural evolution, and mechanistic role of nanoparticle precursors (1-6 nm) during silicalite-1 crystallization have been the subjects of prior investigation by combined experimental and modeling techniques. Here we investigate for the first time the effects of zeolite growth modifiers (ZGMs) on MFI precursors. ZGMs are organic molecules that alter the anisotropic rate(s) of crystal growth as a means of tailoring crystal size and/or habit. We show that most ZGMs have little effect on precursor assembly and evolution during the prenucleation stages of silicalite-1 and ZSM-5 synthesis; however, studies at varying alkalinity reveal that pH can be used as a "switch" to tune ZGM speciation and concurrently the colloidal stability of precursors. This has been proven effective for various polyamine compounds, such as spermine, that exhibit divalent (positive) charge near negatively charged nanoparticle surfaces. Our finding is consistent with colloidal models that predict a higher concentration of divalent modifiers within the diffuse double layer surrounding the surfaces of (alumino)silicate precursors. Multivalent polyamines seemingly promote precursor-precursor aggregation at elevated temperature, which is consistent with a proposed hypothesis that modifiers with two or more sufficiently spaced cationic functional moieties are capable of bridging neighboring precursor surfaces, thus overcoming an electrostatic repulsive force that contributes to their colloidal stability. Given the importance of precursor-precursor and precursor-crystal interactions in zeolite nucleation and growth, respectively, our observations provide additional insight into the role of organics in zeolite crystallization.

Lewis Acid Zeolites for Biomass Conversion: Perspectives and Challenges on Reactivity, Synthesis, and Stability

Zeolites containing Sn, Ti, Zr, Hf, Nb, or Ta heteroatoms are versatile catalysts for the activation and conversion of oxygenated molecules owing to the unique Lewis acid character of their tetrahedral metal sites. Through fluoride-mediated synthesis, hydrophobic Lewis acid zeolites can behave as water-tolerant catalysts, which has resulted in a recent surge of experimental and computational studies in the field of biomass conversion. However, many open questions still surround these materials, especially relating to the nature of their active sites. This lack of fundamental understanding is exemplified by the many dissonant results that have been described in recent literature reports. In this review, we use a molecular-based approach to provide insight into the relationship between the structure of the metal center and its reactivity toward different substrates, with the ultimate goal of providing a robust framework to understand the properties that have the strongest influence on catalytic performance for the conversion of oxygenates.

Functionalization of arrays of silica nanochannels by post-condensation

Functionalized arrays of silica nanochannels (ASNCs) were prepared by post-condensation. This synthetic approach allows control of the functional group distribution in a one-pot reaction, while preserving the defined nanoporous structure of the ASNCs.

Organic template-free synthesis of zeolite mordenite nanocrystals through exotic seed-assisted conversion

A facile and organic-template-free route of exotic seed-assisted conversion is proposed to synthesize nano-crystallite assembled MOR zeolite with rich mesopores, high crystallinity, perfect framework, and high activity for large molecule cracking.

Nonclassical from-shell-to-core growth of hierarchically organized SAPO-11 with enhanced catalytic performance in hydroisomerization of n-heptane

A growth inhibitor combined tumbling crystallization to generate hierarchical SAPO-11 with enhanced isomer selectivity in hydroisomerization of n-heptane is reported.

SSZ-13 Crystallization by Particle Attachment and Deterministic Pathways to Crystal Size Control

Many synthetic and natural crystalline materials are either known or postulated to grow via nonclassical pathways involving the initial self-assembly of precursors that serve as putative growth units for crystallization. Elucidating the pathway(s) by which precursors attach to crystal surfaces and structurally rearrange (postattachment) to incorporate into the underlying crystalline lattice is an active and expanding area of research comprising many unanswered fundamental questions. Here, we examine the crystallization of SSZ-13, which is an aluminosilicate zeolite that possesses exceptional physicochemical properties for applications in separations and catalysis (e.g., methanol upgrading to chemicals and the environmental remediation of NO(x)). We show that SSZ-13 grows by two concerted mechanisms: nonclassical growth involving the attachment of amorphous aluminosilicate particles to crystal surfaces and classical layer-by-layer growth via the incorporation of molecules to advancing steps on the crystal surface. A facile, commercially viable method of tailoring SSZ-13 crystal size and morphology is introduced wherein growth modifiers are used to mediate precursor aggregation and attachment to crystal surfaces. We demonstrate that small quantities of polymers can be used to tune crystal size over 3 orders of magnitude (0.1-20 μm), alter crystal shape, and introduce mesoporosity. Given the ubiquitous presence of amorphous precursors in a wide variety of microporous crystals, insight of the SSZ-13 growth mechanism may prove to be broadly applicable to other materials. Moreover, the ability to selectively tailor the physical properties of SSZ-13 crystals through molecular design offers new routes to optimize their performance in a wide range of commercial applications.