Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil

Improved synthetic approaches for preparing small‐sized Ni nanoparticles (d=3 nm) supported on HBEA zeolite have been explored and compared with the traditional impregnation method. The formation of surface nickel silicate/aluminate involved in the two precipitation processes are inferred to lead to the stronger interaction between the metal and the support. The lower Brønsted acid concentrations of these two Ni/HBEA catalysts compared with the parent zeolite caused by the partial exchange of Brønsted acid sites by Ni²⁺ cations do not influence the hydrodeoxygenation rates, but alter the product selectivity. Higher initial rates and higher stability have been achieved with these optimized catalysts for the hydrodeoxygenation of stearic acid and microalgae oil. Small metal particles facilitate high initial catalytic activity in the fresh sample and size uniformity ensures high catalyst stability.     

Dimethylether production on zeolite catalysts activated by Cl-, F- and/or ultrasonication

The chlorinated and fluorinated zeolite catalysts were prepared by the impregnation of zeolites( H-ZSM-5,H-MOR or H-Y) using two halogen precursors( ammonium chloride and ammonium fluoride) in this study. The influence of ultrasonic irradiation was evaluated for optimizing both halogen precursors for production of dimethylether( DME) via methanol dehydration in a fixed bed reactor. The catalysts were characterized by SEM,XRD,BET and NH3-TPD. The reaction conditions were temperatures from 100 to 300 ℃ and a WHSV = 15. 9 h-1. All halogenated catalysts showhigher catalytic activities at all reaction temperatures studied. However, the halogenated zeolite catalysts prepared under ultrasonic irradiation showhigher performance for DME formation. The chlorinated zeolite catalysts show higher activity and selectivity for DME production than the respective fluorinated versions.     

Silica self-assembly and synthesis of microporous and mesoporous silicates

The microstructure of silica in basic aqueous solutions containing organic cations and prepared from monomeric precursors is reviewed and interpreted within the context of classical ideas of self-assembly of molecular aggregates. The solution properties can be understood by using the pseudo-phase separation approach coupled to the acid-base chemistry of silanol groups and the Poisson-Boltzmann equation. The silica nanoparticles frequently observed in these systems have a core-shell structure with silica in the core and the organic cations at the shell. Individual particles are observed when the forces between particles are repulsive-as is the case for small cations such as tetramethylammonium or tetrapropylammonium-and extended structures such as M41S materials are formed when the forces are attractive--as is the case for surfactants such as cetyltrimethylammonium. These ideas are useful to understand the evolution of zeolite synthesis gels from nucleation to crystal growth. Although at room temperature the silica and the organic cations are segregated, upon heating the organic cations are embedded within the particles. This transformation signals the onset of structure direction whereby the size and geometry of the organic cation induce changes in the structure of silica that may lead to zeolite nuclei.     

C2-C2直链烯烃在HY 和H-ZSM-5分子筛上的吸附

采用ONIOM(B3LYP/6-311++G(d,p):UFF)分层计算方法, 研究了C₂-C₅直链烯烃在HY 和H-ZSM-5 分 子筛上的吸附性质. 理论计算结果表明: 烯烃与分子筛的Br?nsted 酸性位相互作用形成π配位超分子复合物; 随着碳链的增长, 烯烃的吸附能增加, 增加量近似为一个常数(HY 分子筛: 约12 kJ·mol^-1; H-ZSM-5 分子筛: 约 25 kJ·mol^-1), 与烷烃在分子筛上的吸附具有相同的规律. 双键位置对烯烃的吸附能影响很大, 2位烯烃的吸附能 要远大于1 位烯烃的吸附能. 不同类型分子筛对烯烃的吸附性能也有很大差别, 由于局域效应的影响, 小孔径 H-ZSM-5分子筛上的吸附能大于大孔径的HY分子筛,而且碳链越长,这种差别越大.从微观结构上看,吸附的烯 烃与H-ZSM-5分子筛酸性位的距离要远大于它们与HY分子筛酸性位的距离, 这是由于不同类型分子筛的微孔 结构产生的范德华作用是不同的,这种作用随着孔径的减小而增强.前线轨道分析表明, 对于小分子烯烃,大孔径 HY分子筛对其催化活性相近,而小孔径H-ZSM-5分子筛随着烯烃碳原子数的增加催化活性有减弱的趋势.     

Metal(II) Formates (M = Fe,Co, Ni,and Cu) Stabilized by Tetramethylethylenediamine (tmeda): Convenient Molecular Precursors for the Synthesis of Supported Nanoparticles

γ‐Alumina supported 3d transition‐metal nanoparticles are commonly used catalysts for several industrial reactions, such as Fischer‐Tropsch, reforming, methanation, and hydrogenation reactions. However, the activity of such catalyst is often limited by the low metal dispersion and a high content of irreducible metal, inherent to the conventional preparation methods in aqueous phase. In this context, we have recently shown that [{Ni(μ²‐OCHO)(OCHO)(tmeda)}₂(μ²‐OH₂)] (tmeda=tetramethylethylenediamine) is a suitable molecular precursor for the formation of 1–2 nm large nanoparticles onto alumina. Here, we explore the synthesis of the corresponding Fe, Co, and Cu molecular precursors, namely [{Fe(μ²‐OCHO)(OCHO)(tmeda)}₄], [{Co(μ²‐OCHO)(OCHO)(tmeda)}₂(μ²‐OH₂ )], [Cu(κ²‐OCHO)₂(tmeda)], which are, like the Ni precursor, soluble in a range of solvents, rendering them convenient metal precursors for the preparation of supported metallic nanoparticles on γ‐alumina. Using a specific adsorption of the molecular precursor on γ‐alumina in a suitable organic solvent, treatment under H₂ provides small and narrowly distributed Fe (2.5±0.9 nm), Co (3.0±1.2 nm), Ni (1.7±0.5 nm), and Cu (2.1±1.5 nm) nanoparticles. XAS shows that the proportion of MAl₂O₄ (M = Co, Ni, Cu) is small, thus illustrating the advantage of using these tailor‐made molecular precursors.     

The Link between ZSM-5 Zeolite Crystallization and Mesopore Formation by Leaching

Acid or base leaching are well-established tools in the synthesis of mesoporous zeolites. Previous studies suggest an inherent link between the structure-property relationship of mesoporous zeolites, that is, chemical resistance, pore diameter and distribution, with zeolite synthesis or crystallization conditions. The exact nature and/or origin of this link is currently however, poorly established. Here, we provide evidence how zeolite crystallization conditions influence the leaching behavior and thus structure of mesoporous zeolites. Electron microscopy and in situ small angle X-ray scattering both confirmed the crystallization of ZSM-5 to utilize both nanoparticles and oligomers as elemental building blocks. Utilization of these species is highly depended on supersaturation. The precursor solution of decreased water content favored a faster consumption of nanoparticles compared to its oligomers at the early stage of crystallization. Then the addition of oligomers can heal the surface imperfections and thus the resulting zeolite showed a higher resistance against acid leaching. In contrast, within the precursor solution of increased water content the slower consumption of nanoparticles led to crystals with a less robust rim. Defects existed in the rim due to limited healing by oligomers and, as such, mesopores can be created by the following post-treatment. Precise control over selected crystallization conditions can therefore further aid the design of optimized mesoporous zeolites.     

Synthesis of highly ordered cubic zeolite A and its ion-exchange behavior

Well-ordered cubic zeolites 4A were synthesised using sol–gel process in the presence of different silica and aluminum sources. The aluminum and silica sources determined whether or not zeolites were formed at precise silica/alumina mole ratio. Zeolites were formed only when the aluminum source was sodium aluminate, the silica source was fumed silica, colloidal silica or sodium metasilicate. Our findings indicated that the type of zeolite invariably obtained was 4A and SEM images indicated that the produced zeolites are cubic shaped crystals with planar surfaces and well-defined edges and sharp crystals. In turn, synthesis parameters are seen to have a significant effect in maximizing heavy metals uptake (for example Cu²⁺, Cr³⁺, Cd²⁺ and Ni²⁺) by synthesized zeolites. Zeolite 4A gave better heavy metal uptakes than amorphous or non-zeolite crystalline materials. This was attributed to higher ion-exchange capacity and higher BET specific surface area 445 m²/g and pore volume 0.141 cm³/g. The latter attribute possibly translates to greater accessibility of ion-exchange sites and selectivity towards metal type by this zeolite followed the sequence: Cu²⁺ > Cr³⁺ ≥ Cd²⁺ > Ni²⁺.     

Hot-Electron Photodynamics in Silver-Containing BEA-Type Nanozeolite Studied by Femtosecond Transient Absorption Spectroscopy

Silver cations were introduced in nanosized BEA-type zeolite containing organic template by ion-exchange followed by chemical reduction towards preparation of photoactive materials (Ag⁰-BEA). The stabilization of highly dispersed Ag⁰ nanoparticles with a size of 1–2 nm in the BEA zeolite was revealed. The transient optical response of the Ag-BEA samples upon photoexcitation at 400 nm was studied by femtosecond absorption. The photodynamic of the hot electrons was found to depend on the sample preparation. The lifetime of the hot electrons in the Ag−BEA samples containing small Ag nanoparticles (1–2 nm) is significantly shortened in comparison to bear Ag nanoparticles with a size of 10 nm. While for the larger Ag nanoparticles, the energy absorbed in the conduction band is decaying by electron-phonon coupling into the metal lattice, the high surface-to-volume ratio of the small Ag nanoparticles favors the dissipation of the energy of the hot electrons from the metal nanoparticles (Ag⁰) towards the zeolitic micro-environment. This finding is encouraging for further applications of Ag-containing zeolites in photocatalysis and plasmonic chemistry.     

Effect of Sodium Concentration on the Synthesis of Faujasite by Two-step Synthesis Procedure

The relationship between the concentration of sodium cations and the properties of faujasite(FAU) zeolite was investigated using a two-step synthesis procedure including (1) formation of amorphous aluminosilicate precursors and separation of amorphous nanoparticles, and (2) transformation of these amorphous particles into zeolite crystals by treatment with alkali solutions(NaOH). Three representative samples including two nano-sized zeolites and one micron-sized zeolite were prepared using different concentrations of sodium hydroxide. The crystallization process of these zeolites was studied in detail by Fourier transform infrared(FTIR) spectrometry, nuclear magnetic resonance spectroscopy(NMR), X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), and N₂ adsorption. The results indicated that minor changes in the concertation of inorganic cations can significantly shorten the induction period and crystallization time and thus affect the morphology, size and chemical composition of the zeolite crystals.     

The effects of alkali metal(Na+,K+) on the exchange degree of Hβ zeolite and the catalytic properties of the alkalized zeolites

The effects of alkali metals (Na+,K+) on the exchange degree of Hβ zeolite under different conditions and the conversion of α(or β)-methylnaphthalene over the alkalized zeolites were studied. The results showed that the H+ of Hβ zeolite is totally replaced by the Na+ of NaCl solution, while partially exchanged by the K+ of KC1 solution, there is an exchange equilibrium between the H+ and K+ for Hβ zeolite (Si/Al=17.23) and the value of equilibrium is 88.39. The exchange degree also increases with increasing the Si/Al of the samples. It was suggested that these resluts are attributed to the electrostatic field in the pore of Hβ zeolite and the nature of zeolite and the properties of alkali metal. The isomerization of α(or β)-methylnaphthalene is the main reaction over the samples and it is more favour on the proper acid-base sites of KHβ zeolite.     

Proton activity inside the channels of zeolite L

The proton activity inside the channels of zeolite L has been studied by investigating dye-loaded zeolite L crystals under different conditions, such as water content, nature of the counterions, and nature of the solvent. The discussion is made within the frame of three types of dye-loaded zeolite L systems, classified according to their ability to exchange matter (dyes, cations, solvent, and other small molecules) with the environment. The classification refers to dye-loaded zeolites. The term "closed" and "semi-open" characterize different possibilities of the channels to exchange small molecules, cations, and solvent molecules with the environment, but not dyes. The "open" systems also allow for dye exchange. UV-visible and fluorescence spectroscopy have been used to observe the proton activity inside the zeolite L channels. The influence of the proton activity on the luminescence of encapsulated dyes is discussed, special attention being given to luminescence quenching by excited-state protonation. Partially proton-exchanged zeolite L can be a superacid, whereas for the M-exchanged form (M: K(+), Li(+), Cs(+), Mg(2+), Ca(2+)) the pH ranges from about 2.5 to 3.5. For these last forms, the differences in pH are due to the acid-base reactions of the respective metal cations with water inside the zeolite. Finally, we describe an easy experimental procedure that can be used to tune the proton activity inside the zeolite L to a considerable extent.     

Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods: Effect of acidity of active Ga species on the catalytic performance

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO⁺ species ([GaO⁺]^a) that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO⁺]^a species with stronger Lewis acid sites produced a better synergism with moderate Brønsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga₂O₃ phase and small amounts of GaO⁺ species that are mainly located on the external surface ([GaO⁺]^b), which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples (Gax-NZ5) exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield (i.e., 65.4 wt%) was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.     

纳米分子筛的合成及硫化氢吸附性能

利用无模板水热法合成纳米尺寸的小孔SOD型和大孔X型分子筛, 并考察了其硫化氢脱除性能. 通过对比两种分子筛的硫化氢吸附性能, 证实分子筛对硫化氢的吸附主要集中于孔道内和可及的活性位. 考察了晶粒尺寸、 体积空速和吸附温度等因素对硫化氢吸附的影响, 发现纳米尺寸X型分子筛具有更大的硫容, 并且在低温和低空速下分子筛中的硫化氢分子易于脱除. 随后对纳米X型分子筛进行了金属离子交换改性, 发现Cu改性的分子筛硫容优于其它离子改性的吸附剂, 能达到20.6 mg/g. NaX-N和Cu-NaX-N再生后的硫容分别为新鲜分子筛的62.4%和78.5%.     

Targeted Synthesis of Ultrastable High‐Silica RHO Zeolite Through Alkali Metal–Crown Ether Interaction

High‐silica RHO zeolite was directly synthesized using an alkali metal‐crown ether (AMCE) complex as organic structure‐directing agent (OSDA). Derived from the UV‐vis spectra and zeolite patterns, the crown ether‐cesium cation interaction was found to have crucial effect on the enhancement of silica content within the zeolite framework. The synthesized RHO zeolites possess up to four times larger silica/alumina ratio (SAR) values than that in their conventional form, which gives them extraordinarily rigid frameworks even after hydrothermal aging under 800 °C. Compared to commercial zeolites, copper‐exchanged high‐silica RHO zeolites demonstrate considerably high reaction activity in NO_X removal, making them promising candidates for diesel exhaust treatment.     

Titanosilicate zeolite precursors for highly efficient oxidation reactions

Titanosilicate zeolites are catalysts of interest in the field of fine chemicals. However, the generation and accessibility of active sites in titanosilicate materials for catalyzing reactions with large molecules is still a challenge. Herein, we prepared titanosilicate zeolite precursors with open zeolitic structures, tunable pore sizes, and controllable Si/Ti ratios through a hydrothermal crystallization strategy by using quaternary ammonium templates. A series of quaternary ammonium ions are discovered as effective organic templates. The prepared amorphous titanosilicate zeolites with some zeolite framework structural order have extra-large micropores and abundant octahedrally coordinated isolated Ti species, which lead to a superior catalytic performance in the oxidative desulfurization of dibenzothiophene (DBT) and epoxidation of cyclohexene. It is anticipated that the amorphous prezeolitic titanosilicates will benefit the catalytic conversion of bulky molecules in a wide range of reaction processes.

Titanosilicate zeolite precursors, with open structures of zeolite units and high amounts of catalytically active Ti species, show superior catalytic performance in the oxidative reactions.     

How Water and Ion Mobility Affect the NMR Fingerprints of the Hydrated JBW Zeolite: A Combined Computational-Experimental Investigation

An important aspect within zeolite synthesis is to make fully tunable framework materials with controlled aluminium distribution. A major challenge in characterising these zeolites at operating conditions is the presence of water. In this work, we investigate the effect of hydration on the ²⁷Al NMR parameters of the ultracrystalline K,Na-compensated aluminosilicate JBW zeolite using experimental and computational techniques. The JBW framework, with Si/Al ratio of 1, is an ideal benchmark system as a stepping stone towards more complicated zeolites. The presence and mobility of water and extraframework species directly affect NMR fingerprints. Excellent agreement between theoretical and experimental spectra is obtained provided dynamic methods are employed with hydrated structural models. This work shows how NMR is instrumental in characterising aluminium distributions in zeolites at operating conditions.     

STUDY ON THE INTERACTION BETWEEN POLYVINYLPYRROLIDONE AND PLATINUM METALS DURING THE FORMATION OF THE COLLOIDAL METAL NANOPARTICLES

Several PVP-stabilized colloidal platinum metals nanoparticles have been synthesized and characterized by FTIR and TEM.Comparing with the pure PVP,carbonyl groups of PVP in the mixture of PVP and the metal precursors or in the PVP-stabilized metal nanoparticles have obvious peak shifts in FTIR spectra.The peak shifts reveal the interaction between PVP and the metal species.The interaction between PVP and metal precursors has effect on the formation of the colloidal metal nanoparticles.Strength of the int...     

Phase Transformation Behavior of a Two‐Dimensional Zeolite

Understanding the molecular‐level mechanisms of phase transformation in solids is of fundamental interest for functional materials such as zeolites. Two‐dimensional (2D) zeolites, when used as shape‐selective catalysts, can offer improved access to the catalytically active sites and a shortened diffusion length in comparison with their 3D analogues. However, few materials are known to maintain both their intralayer microporosity and structure during calcination for organic structure‐directing agent (SDA) removal. Herein we report that PST‐9, a new 2D zeolite which has been synthesized via the multiple inorganic cation approach and fulfills the requirements for true layered zeolites, can be transformed into the small‐pore zeolite EU‐12 under its crystallization conditions through the single‐layer folding process, but not through the traditional dissolution/recrystallization route. We also show that zeolite crystal growth pathway can differ according to the type of organic SDAs employed.     

A Pd@Zeolite Catalyst for Nitroarene Hydrogenation with High Product Selectivity by Sterically Controlled Adsorption in the Zeolite Micropores

The adsorption of molecules on metal nanoparticles can be sterically controlled through the use of zeolite crystals, which enhances the product selectivity in hydrogenations of reactants with more than one reducible group. Key to this success was the fixation of Pd nanoparticles inside Beta zeolite crystals to form a defined structure (Pd@Beta). In the hydrogenation of substituted nitroarenes with multiple reducible groups as a model reaction, the Pd@Beta catalyst exhibited superior selectivity for hydrogenation of the nitro group, outperforming both conventional Pd nanoparticles supported on zeolite crystals and a commercial Pd/C catalyst. The extraordinary selectivity of Pd@Beta was attributed to the sterically selective adsorption of the nitroarenes on the Pd nanoparticles controlled by the zeolite micropores, as elucidated by competitive adsorption and adsorbate displacement tests. Importantly, this strategy is general and was extended to the synthesis of selective Pt and Ru catalysts by fixation inside Beta and mordenite zeolites.     

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.