Nan Ren

Zeolitization of diatomite to prepare hierarchical porous zeolite materials through a vapor-phase transport process

In this study, we report a new, simple approach to the preparation of hierarchical structured zeolites through transforming the diatomaceous silica into zeolite by a vapor-phase transport (VPT) method. The morphology and macro-porosity of the diatomite are well preserved even in the samples with zeolite content higher than 50%. The products possess high mechanical strength and hydrothermal stability, and are thus promising for application in catalysis, adsorption and separation. The influence of the zeolite structures, the amount of adsorbed seeds, and the VPT treatment time and temperature on the crystallinity of the resulting materials are discussed. Powder XRD, SEM, TEM, IR and N2 adsorption–desorption measurements are employed to monitor the VPT treatment process.

Fabrication of hollow zeolite microcapsules with tailored shapes and functionalized interiors

Abstract Hollow zeolite microcapsules with spherical and various non-spherical shapes were fabricated through a novel strategy involving the crystallization of mesoporous silica (MS) particles. This conversion process was achieved by vapor phase transport treatment of MS particles which were pre-seeded by nanozeolite via the electrostatic assembly technique. The capsule shell was composed of closed packed zeolite crystals growing from the initial seeds by consuming the silica “nutrition” in the internal MS cores. The effects of seed size and seed type on the transformation of MS particles were investigated in detail. More importantly, guest species (e.g. Fe 2 O 3 and Ag nanoparticles) which had been incorporated in the mesopores of the MS particles could be spontaneously encapsulated inside the generated capsules during the MS consumption process, thus, hollow zeolite capsules with functionalized interiors could be easily fabricated.

A facile route to synthesize endurable mesopore containing ZSM-5 catalyst for methanol to propylene reaction

A novel route is proposed for the preparation of mesopore containing zeolite ZSM-5 via in situ hydrothermal treatment of a solution containing alkali-dissolved SBA-15 containing carbonized surfactant P123 in the mesopores; it exhibited prominent stability enhancement for methanol to propylene reaction.

Mesoporous microcapsules with noble metal or noble metal oxide shells and their application in electrocatalysis

A versatile peripheral-pore-nanocasting method is employed to fabricate a series of novel microcapsules with mesoporous shell of noble metal or noble metal oxides, including Pt, PdO, RuO2 and IrO2. The shell thickness of these hollow microcapsules can be adjusted by controlling the depth of 3-amino-propyltriethoxysilane (APS) modification. By pre-filling the guest species or their precursors into the 3-D pores of HMS (hexagonal mesoporous molecular sieves) spheres, an interesting material with a “sphere in shell” structure could be fabricated via the same method. Both the mesoporous platinum hollow microcapsules and carbon spheres encapsulated in platinum microcapsules have shown high mass-normalized activities as a catalyst in the oxidation of methanol, a fundemantal reaction in direct methanol fuel cells (DMFC).

Fabrication of compact silver nanoshells on polystyrene spheres through electrostatic attraction.

Nanoshells composed of close-packed silver nanocrystals have been fabricated on polystyrene spheres via direct electrostatic attraction at appropriate pH; the thickness and roughness of the shell can be readily controlled through a layer-by-layer technique.

Synthesis of silver nanoparticles via electrochemical reduction on compact zeolite film modified electrodes

Monodisperse silver nanoparticles with different sizes were synthesized by electrochemical reduction inside or outside zeolite crystals according to the silver exchange degree of compact zeolite film modified electrodes.

The relationship between sub-micrometer sized ZSM-5, slice-like (lamellar) keatite and hollow α-quartz particles: a phase transformation study

Crystallization–transformation processes in the reaction mixture: (4Na2O–0.1667Al2O3–100SiO2–4000H2O) seeded with 4 wt% of 260 nm silicalite-1 seeds, at 170 °C were investigated by various experimental methods such as, X-ray diffraction (XRD), electron diffraction (ED), scanning-electron microscopy (SEM), transmission electron microscopy (TEM), particle size analysis (PSD), pH measurement, atomic absorption spectrometry (AAS) and dynamic light scattering (DLS). Analysis of the obtained results have shown that the crystallization–transformation takes place by a chain of processes: (i) dissolution of amorphous silica (used as silica source), and formation of 10–50 nm precursor species (PSs), (ii) spending of the PSs for both the limited growth of zeolite ZSM-5 on the surfaces of silicalite-1 seed crystals and formation of worm-like particles (WLPs), (iii) formation of condensed aggregates (CAs) by aggregation/condensation of the WLPs; a part of the composite particles, composed of the silicalite-1 core and ZSM-5 shell are incorporated into CAs, (iv) nucleation of keatite followed by solution-mediated transformation of the condensed WLPs into lamellar keatite, (v) nucleation of α-quartz followed by solution-mediated transformation of keatite into α-quartz; a part of the nuclei of α-quartz are formed on the surface of the core–shell silicalite-1–ZSM-5 composite species and another part of the nuclei are formed in the vicinity of the dissolving keatite and (vi) dissolution of the silicalite-1 core and a major part of the ZSM-5 “interlayer” of the composite particles (α-quartz shell-ZSM-5 “interlayer”-silicalite-1 core) and formation of hollow α-quartz particles with a thin ZSM-5 layer on the inner surfaces of the hollow α-quartz particles. Occurrences of all the mentioned processes are rationally analyzed and explained on the basis of the existing and newly obtained knowledge.

Zeolite Nanocrystals: Hierarchical Assembly and Applications

Publisher Summary This chapter reviews the methods for the hierarchical assembly of zeolitic materials with different structures by employing colloidal nanozeolites and/or sub-units as building blocks. The hierarchical assembly strategy is the best way to realize the construction of the “macrostructures” via rational assembly or moulding approaches. The assembled hierarchical architecture may also endow the materials with novel characteristics through integrating the multifunctionalities and porosities in one structure, which provide more opportunities for the applications ranging from catalysis to electronic devices. The interests for preparation and assembly of nanozeolites are based on the facts that the reduction of crystals size could bring about higher efficiency in catalytic processes or could offer applicable opportunities in the new fields. Following the fruitful achievements of the conventional zeolites in both petrochemical and fine chemical catalysis, the application of nanozeolite in the area of catalysis became the original motivation that triggered the burst of zeolite nanotechnology. The rich acid sites on external surface of nanozeolites make them possessing a high activity for the reaction of large molecules, while their abundant pore-opening and short diffusion path would greatly enhance their tolerance to coking. Their supplied surface acidity could also be used in bi-functional enzymatic-acid catalysts. With the deepening of the understanding on the special interaction on the surface/interface between nanozeolite and biomolecules, various nanozeolite materials including dispersed colloidal zeolites, hierarchical nanozeolite assemblies, and layered zeolitic nanocompounds have been studied in their bioapplication. By using various assembly methods, some biocompatible microdevices such as the enzymeimmobilized sensors and bio-chips could be well constructed.

Crystallization of Sub-Micrometer Sized ZSM-5 Zeolites in SDA-Free Systems

The seed-induced crystallization system has been adopted for the synthesis of sub-micrometer sized zeolite ZSM-5 in the absence of organic structure directing agent (SDA). The structural (phase purity), particulate (sizes and morphologies) and chemical compositions (framework Si/Al ratios) of the crystalline end products could be well controlled via the variation of synthesis parameters such as size and amount of silicalite-1 seed nanocrystals, batch alkalinity, excess of sodium ions and ageing of reaction mixtures. More importantly, the crystallization mechanism has also been revealed as a typical linear, size-independent growth process on the surface of silicalite-1 seed nanocrystals, embedded in the gel matrix, without the formation of new nuclei either on the surface of growing seed crystals or in the gel matrix. The critical processes happened during crystallization have also been characterized by different methods and evaluated by population balance modeling approach.

Synthesis and functionalization of mesoporous zirconium (IV) phosphate-phenylphosphonate with small mesopores

Abstract The synthesis and functionalization of mesoporous zirconium (IV) phosphate-phenylphosphonate have been systematically described as a new non-siliceous mesoporous material. The mesostructure formation and functionalization could be proved through XRD, BET, 31 PMASNMR, IR, TEM and TGA characterization methods. The samples prepared have worm-like 3D-connected tubular mesopores, higher surface areas and better thermal stabilities in contrast to the layered analogs. The amount of phenyl groups inside the samples could be adjusted by controlling the molar ratio of the phosphoric and phosphonic acids during the synthesis procedure. Furthermore, the phenyl groups inside the pore channels of samples can be easily functionalized through phenyl substitution reactions to incorporate sulphonate, bromic, nitro groups. After functionalization, the sulphonated and brominated samples still kept the mesostructure but the nitrified sample did not. The results of the NH 3 adsorption microcalorimetric and TGA measurements demonstrated that the sulphonated sample had more strong acid sites and higher thermal stability, and consequently possess higher acid catalytic activity for the liquid phase esterification reaction between benzoic acid and methanol.