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A series of Zr–Al-MWW zeolites with different Zr state and layer-stacking structure are successfully synthesized via direct grafting zirconocene dichloride onto the external silanols of three kinds of MWW zeolites, i.e. MCM-22 with multilayered structure, ITQ-2 (through layer delaminated route) and OL-MWW (by direct hydrothermal synthesis) with oligolayered structure. The structure, porosity and state of grafted Zr species are distinctly different among the three Zr–Al-MWW zeolites. Zr-OL-MWW possesses the highest content of single Zr atoms with an ideal micro-meso-macro pore system, while Zr-MCM-22 and Zr-ITQ-2 contain two kinds of Zr species (ZrO 2 clusters and single Zr atoms) coexisting in various proportions. The high dispersion of single Zr atoms on OL-MWW can be assigned to the large amount of external silanols of OL-MWW. The as-prepared three bi-functional Zr–Al-MWW zeolites are used for the cascade Meerwein-Ponndorf-Verley (MPV) reduction and etherification (ETH) reaction. Among them, Zr-OL-MWW shows dramatically higher conversion of cinnamaldehyde and yield of 1-cinnamyl 2-propyl ether than Zr-MCM-22 and Zr-ITQ-2, owing to the higher catalytic activity of Lewis acid centers from single Zr atoms, as well as more integrated framework Al sites as Brønsted acid centers with good accessibility. This study offers a simple and efficient strategy to construct Lewis-Brønsted acidic zeolites with exposed heteroatom sites and integrated framework structure, which will provide especial potential in the catalytic conversion of macromolecules. Bi-functional Zr–Al-MWW zeolites, i.e. Zr-MCM-22, Zr-ITQ-2 and Zr-OL-MWW were synthesized by direct grafting of zirconocene dichloride onto the external silanols of three zeolite matrixes, and applied in the Lewis-Brønsted cascade reaction. [Display omitted] • Bi-functional Zr–Al-MWW zeolites were synthesized by a direct grafting strategy. • Zr site state correlated to the matching between the amount of external silanols and the content of grafted Zr species. • Oligolayered MWW nanosheet with abundant external silanols produced more single Zr sites than multilayered MWW zeolite. • The ideal hierarchical porosity, integrated Al sites and exposed singe Zr sites provided superior catalytic performance. [ABSTRACT FROM AUTHOR]

Series of meso/microporous zeolite Y composites with adjustable hierarchy factors (HF) from 0.04 to 0.16, are prepared from commercial NaY zeolite (Si/Al = 2.5) by the two-step method with first lactic acid leaching and then CTAB-assisted ammonia treatment. The essential effect of lactic acid on the formation of diverse mesoporous domains in microporous crystals are systematically investigated. A possible scheme is proposed. The lactic acid leaching process is found to be very crucial to controllably remove the framework aluminum and regulate the amount/size of intra-crystal amorphous silicon-rich domains, which then evolve to mesostructures within the microporous crystals via structural re-arrangement/dissolution-reassembly process during the CTAB-assisted ammonia treatment. Varying the lactic acid concentrations would result in different crystallinity preservations and diverse proportions/dispersity of mesoporous regions, and thus well tune the HF values of the final composites. The zeolite Y composites with moderate mesoporosities allow much better performances in the acetalization reactions of cyclohexanone with pentaerythritol due to the improved diffusion ability of large sized guest molecules, whereas accompanying loss of acidity would depress reactivities of the treated samples for dehydration of small isopropanol. [ABSTRACT FROM AUTHOR]

Fe 2 O 3 nanoparticles were dispersed onto SiO 2 by impregnating amorphous SiO 2 spheres with Fe(NO 3 ) 3 followed by spray drying and calcination. Interestingly, the amorphous SiO 2 spheres in the sample could be converted into Silicalite-1 nanowires after being hydrothermally treated in the presence of a mixture of ethylenediamine and triethylamine (dual templates) for over 4 days, whereas the Fe 2 O 3 nanoparticles were still highly dispersed on the formed Silicalite-1 nanowires. Meanwhile, a fraction of Fe(III) species entered the zeolitic framework. Relevant characterization was conducted using X-ray fluorescence (XRF), N 2 adsorption–desorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, electron paramagnetic resonance (ESR), X-ray photoelectron spectroscopy (XPS), and H 2 -temperature-programmed reduction (H 2 -TPR). The catalytic properties of the samples were studied using CO oxidation, N 2 O decomposition, and selective reduction of NO as probe reactions. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the influences of excess amount of sodium ions and the way/duration of ageing of the reaction mixture (hydrogel) on structural, particulate, morphological and chemical properties of the crystalline end products obtained by hydrothermal treatment (heating at 483K for 2h) of the TPA-free reaction mixture: 1.0Al2O3/100SiO2/xNa2O/4000H2O/yNa2SO4 (0.4⩽(x + y)⩽100) seeded by silicalite-1 nanocrystals (260nm, 4wt.% of silica in gel mixture), was investigated by different characterization methods such as, powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), particle size distribution (PSD) measuring by laser light scattering (LLS) and X-ray fluorescence (XRF). The obtained results showed that addition of sodium sulfate in low-alkaline reaction mixture enhances the aggregation of the particles of colloidal silica and formation of gel by the action of sulfate oxy-anions while in high-alkaline reaction mixtures the condensation process takes place on the surface of the crystalline end products. Excess amount of sodium ions do not increase the crystallization rate thus showing that the rate-determining factor is concentration of “free” low-molecular weight silicate species, determined by the alkalinity of system. On the other hand, addition of sodium sulfate considerably reduces the formation of crystal aggregates, by combined chemical and electrical interactions. Ageing of the reaction mixture (hydrogel) mainly influences the particle size distribution of the crystalline end products, which is explained by the change in the relative rates of crystal growth and crystal aggregation with the time of ageing. However, hydrogel ageing does not affect the size and number of crystals in the crystalline end product, showing that the growth precursor particles form during hydrothermal treatment of the reaction mixture and not during its room-temperature ageing. [Copyright &y& Elsevier]

Abstract: In this work, the influence of alkalinity, A =[Na2O/H2O]b (b=batch), of the reaction mixture on structural, particulate, morphological and chemical properties of the crystalline end products obtained by hydrothermal treatment (heating at 483K for 2h) of the TPA-free reaction mixture: 1.0Al2O3/100SiO2/xNa2O/4000H2O seeded by silicalite-1 nanocrystals (260nm, 4wt.% of silica in gel mixture), was investigated by different characterization methods such as powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), particle size distribution (PSD) measuring by laser light scattering (LLS) and X-ray fluorescence (XRF). The obtained results showed that, when silicalite-1 having the size of 260nm was used as seed, fully crystalline product (silicalite-1/ZSM-5) having the size in the range of 400–600nm and Si/Al ratio of 10–18 can be obtained for 0.006⩽ A ⩽0.01, in less than 2h. However, the product obtained at low (A ⩽0.005) or high (A ⩾0.011) alkalinities possess amorphous and/or phillipsite impurities, respectively. The influence of alkalinity, A, on the mentioned properties of the crystalline end product was discussed in relation to the influence of alkalinity on the relevant critical process of zeolite ZSM-crystallization in the absence of organic templates. [ABSTRACT FROM AUTHOR]

Abstract: Columned ZSM-5 zeolite monoliths with hierarchical structure and excellent mechanical strength were successfully prepared by a hydrothermal transformation method. The pre-formed extrudates of aluminosilicate embedded with β zeolite were subjected to a hydrothermal synthesis system and the hierarchical porous ZSM-5 zeolite monoliths with the same columned shape were obtained after the hydrothermal treatment. The intra-particle hollow structure formed during hydrothermal synthesis was attributed to the digestion of inner β zeolite accompanying with the growth of ZSM-5 zeolite shell. The related data of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) analysis, N2-sorption experiment and mercury intrusion prosimetry (MIP), showed ZSM-5 zeolite monolith had enriched multi-porosity and excellent mechanical stability, which contribute to its further application in field of catalysis and separation. The obtained hierarchical ZSM-5 zeolite monoliths showed superior catalytic performance in α-pinene isomerization for their proper acidity and good diffusion, compared with the ZSM-5 zeolite sample prepared from the precursor without β zeolite. [Copyright &y& Elsevier]

Abstract: In the present work, the detailed formation process of hollow silicalite-1 microcapsules (HSMs) was investigated in the hydrothermal system of silicalite-1 pre-seeded mesoporous silica spheres (MSSs). The effects of the starting gel composition together with the hydrothermal synthesis conditions such as alkalinity, tetra-propylammonium cation (TPA+) content, and temperature on the features of microcapsules are comprehensively discussed, and a related mechanism is presented. It is found that the matching of core dissolution rate (R cd) and silicalite-1 shell inter-growth rate (R si) is crucial for the formation of perfect HSMs. The proper addition of tetraethoxy-orthosilane (TEOS) as supplemental silica source could accelerate R si whereas excess TEOS will dramatically suppress the consumption of siliceous species from the MSS cores owing to the higher activity of siliceous species in TEOS for the zeolite crystallization. The excellent HSMs with dense inter-grown shell structure as well as perfect hollow center can be fabricated by controlling the relative rates of the dissolution of silica template core and the formation of zeolitic shell. [Copyright &y& Elsevier]

Abstract: A method based on seed surface crystallization (SSC) mechanism has been proposed for facile, rapid, controllable and low-cost synthesis of ZSM-5 zeolite with submicron-size and interesting core–shell structure. The crystallization process of the ZSM-5 zeolite with all sizes can be accomplished within 2.5h. The morphology and size of zeolite ZSM-5 products can both be facilely adjustable in the domain of 270–1100nm depending upon the characters of silicalite-1 seeds, while the thickness of aluminum-containing zeolite ZSM-5 shells can be well tuned by changing the amount of silicalite-1 seed. More interestingly, the siliceous silicalite-1 seeds within the obtained zeolite crystals could be selectively removed by alkaline treatment. By systematically tracking the crystallization process combined with mathematical analysis, the crystallization of ZSM-5 zeolites in the reaction system is revealed as SSC mechanism with a size-independent, linear growth process. Their crystal growth rate is calculated as c.a. 0.15μmh−1 regardless of the seed size and amount. [Copyright &y& Elsevier]

Abstract: The preparation and mechanism investigation of mesoporosity and morphology are extremely important in the field of mesoporous materials. By using neutral amines as templates and alcohols as co-solvents, a series of HMS with different morphologies and mesoporosities are obtained. When long alkyl chain surfactant (n ⩾16) and short alkyl chain alcohol (CH3OH and C2H5OH) are employed, the increasing alcohol content induces the morphological transformation from lotus-leaf-like flake, to aggregated flake, potato-like vesicle, sphere, and finally to solid nanoparticle. When using short alkyl chain surfactant (n ⩽14) and long alkyl chain alcohol (C3H7OH), hollow vesicle, cracked sphere, sphere and mesoporous nanoparticle are successively obtained with the increase of alcohol content. Compared with the conventional mesoporous materials, HMS with these special morphologies has a unique regionally distributed dual meso-structure. By systematically analyzing the effects of co-solvent and surfactant, it is found that the morphology of the product is mainly determined by the initial surfactant micelle which can be adjusted by the type and concentration of surfactant and alcohol. Moreover, with progress of reaction, the decrease of surfactant concentration and the increase of silica polymerization degree would induce the mesophase evolution of product from 2D lamella-like to 3D wormholelike meso-structures, leading to the formation of dual meso-structured HMS products. The understanding of these processes is helpful for preparing mesoporous materials with various morphology and meso-structure for catalysis, separation and other application fields. [Copyright &y& Elsevier]

Abstract: In the present work, a microwave-assisted two-step hydrothermal procedure was proposed successfully to prepare various zeolite nanocrystals (e.g., silicalite-1, ZSM-5, LTL, BEA and LTA) with controllable size, morphology and SiO2/Al2O3 ratio. The effects of the starting gel composition (such as water content, alkalinity and ratio of SiO2/Al2O3) as well as the hydrothermal synthesis condition (temperature and time) on the size of the zeolite nanocrystals have been studied in detail. It is found that high synthesis temperature and long reaction time benefit the growth of all the referred zeolite nanocrystals. However, the effects of the gel composition are very complex to different kinds of nanozeolites. For the nanozeolites crystallized in low alkalinity systems (e.g., ZSM-5, BEA and LTA), both increasing the alkalinity and decreasing the water content accelerate their nucleation process and thereby result in the decrease of their crystal size. On the contrary, for those prepared in high alkalinity systems (e.g., LTL and silicalite-1), an inversed trend could be observed. Moreover, the change of SiO2/Al2O3 ratio in the starting gel greatly affects the size of nanozeolite ZSM-5 and LTL, but slightly influences that of nanozeolite BEA. These results would provide a solid foundation to fully exploit the traditional and untraditional applications of various nanozeolites. [Copyright &y& Elsevier]

Abstract: A series of MCM-22 zeolites were prepared by hydrothermal synthesis and subsequent dealumination by oxalic/citric acid leaching and steaming. The structural and acidic properties of the prepared samples were characterized by methods of XRD, ICP-AES, 27Al MAS NMR, pyridine-adsorbed IR and NH3-TPD. The results indicated that the sample treated by oxalic acid (MCM-22O) has the lowest aluminum content while the samples treated by steam have little change of the aluminum content. Unusually, sample MCM-22O possessed the strongest acidity among the dealuminated samples in spite of its lowest content of aluminum. It may be due to its least content of extraframework aluminum, which may lead to the weakening of acidity. Additionally, the prepared zeolites were mixed with a methanol synthesis catalyst and then applied in the process of syngas to dimethyl ether. Citric acid treated sample performed best with the least generation of byproducts, which have been well related to its structural and acidic properties. [Copyright &y& Elsevier]

Thin zeolite films with thicknesses from several hundred nanometers to a few micrometers have been fabricated through electrophoretic deposition (EPD) in acetylacetone (Acac) and/or isopropyl alcohol (IPA). Various types of nanosized zeolites with different Si/Al ratios ranging from 1.6 (zeolite LTA) to nearly infinity (silicalite-1) were applied to prepare the EPD suspensions and showed different behaviors in EPD. The EPD rate of zeolite particles in non-aqueous medium was much higher than that in aqueous system mainly due to the high voltage applied, and consequently the whole process was usually completed in a few seconds. It was found that the Al/(Si + Al) ratios of zeolites and the chemical/physical properties of the EPD medium were two crucial factors which affected the thickness and density of the zeolite films prepared by EPD. The zeolite films fabricated through EPD could be effectively densified by secondary growth to prepare compact zeolite membranes. [Copyright &y& Elsevier]

Ultrathin nanozeolite films were prepared on the surface of Pt and glass carbon electrodes using nanoscale zeolite particles as building block via a layer-by-layer (LbL) technique or by a secondary growth method. Compared to conventional zeolite-modified electrodes, the nanozeolite film modified ones (nanoZMEs) prepared by these methods exhibit good membrane morphologies with controllable thickness in nanometer scale and large zeolite/electrode contact areas due to the nanoscale zeolite film attached directly to the electrode. Ag+, Cd2+ and Pb2+ were selected as examples to evaluate the electrochemical performance of nanoZMEs with designed thickness. With the same thickness of zeolite layer, nanoZMEs prepared by the LbL technique possess short preconcentration and response time, while nanoZMEs fabricated through the secondary growth method exhibit high accumulation ability and ion exchange selectivity. It is found that besides the inherent ion exchange selectivity of the zeolite layer, the transport rate of ions in the zeolite layer toward the electrode surface is an important factor that affected the electrochemical selectivity of the ZMEs. [Copyright &y& Elsevier]

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. Fe2O3 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. [Copyright &y& Elsevier]

Paper is the most important writing carrier and its degradation (acidification, aging, and ink removal) is a major issue in the protection of cultural heritage. In this work, we first propose alkali ion-exchanged Y zeolites (Ae-Y) as superior deacidification agents for paper. Their features such as the high surface area, adjustable alkali ion content, strength, good structural stability, and safety/non-toxicity or biocompatibility are very promising for preserving paper-based materials, as demonstrated by aging experiments carried out on both historical wood-pulp paper and modern hand-made bamboo paper samples. Through H 2 O-mediated dispersion of Ae-Y in target paper samples, the pH of the paper can be modified to a neutral or weakly basic state, and can be maintained for a long time even under harsh accelerated aging conditions. Meanwhile, the Ae-Y coating hardly alters the chromatic aberration and water wettability of papers. This new deacidifying agent does not trigger color changes in alkali-sensitive pigments (i.e., does not cause fading or blanching of pigments). Moreover, a systematic evaluation of the structure-performance relationship indicates the important roles of adequate accessible basic sites and controllable and mild basicity of Ae-Y in the long-term deacidification, anti-aging, and anti-fading effects exerted on paper relics. These findings not only shed light on the design of protective materials for paper-based cultural relics but also expand our knowledge on the deacidification and protection mechanisms of zeolites. Image 1 • Alkali ion-exchanged Y zeolites are proposed as deacidifying agents for paper. • They may be better alternatives in aqueous phase than generally used MgO and CaO. • Their superior performance is due to adequate accessible and mild basic sites. • The zeolite coatings hardly alter chromatic aberration and wettability of paper. • The zeolite coatings do not cause fading or blanching of alkali-sensitive pigments. [ABSTRACT FROM AUTHOR]