Presence Of Organic Template Research Articles

Recent Advances in the Seed-Directed Synthesis of Zeolites without Addition of Organic Templates.

Zeolites have been widely employed in fields of petroleum refining, fine chemicals and environmental protection, but their syntheses are always performed in the presence of organic templates, which have many drawbacks such as high cost and polluted wastes. In recent years, the seed-directed synthesis of zeolites has been paid much attention due to its low-cost and environmentally friendly features. In this review, the seed-directed synthesis of Al-rich zeolites with homonuclear and heteronuclear features, the seed-directed synthesis of Si-rich zeolites assisted with ethanol and the utility of seed-directed synthesis have been summarized. This review could help zeolite researchers understand the recent progress of seed-directed synthesis.

Targeted synthesis of zeolites from calculated interaction between zeolite structure and organic template.

Zeolites, a class of silica-based porous materials, have been widely employed in the chemical industry for uses such as sorption, separation, catalysis and ion exchange. Normally, the synthesis of zeolites is performed in the presence of organic templates via a trial-and-error route, which is labor-intensive and empirical. In recent years, theoretical simulation from the interaction between a zeolite structure and an organic template has been used to guide the synthesis of zeolites, which is time-saving. In this review, recent progress in the targeted synthesis of zeolites from interaction between a zeolite structure and an organic template are briefly outlined including the design of new templates for zeolite synthesis, preparation of zeolites with new composition, development of novel routes for zeolite synthesis, synthesis of intergrowth zeolites, generation of novel zeolite structures, control of zeolite morphology and modulation of aluminum distribution in zeolites. These targeted syntheses reveal that the minimum energy principle from the theoretical simulation is key for guiding zeolite crystallization. This review will be important for zeolite researchers for rationally synthesizing zeolites and effectively designing new zeolite structures.

New ZnCe catalyst encapsulated in SBA-15 in the production of 1,3-butadiene from ethanol

ABSTRACT ZnO-CeO2/SBA-15 catalysts were prepared by two kinds of solid-state grinding method and used for the production of 1,3-butadiene (1,3-BD) from ethanol. A mixture of SBA-15 (with or without organic template) and metal precursors were ground in solid-state. The obtained catalysts were characterized by TG, N2 adsorption-desorption, TEM, XRD, Py-FTIR and NH3-TPD techniques. Superior dispersion of metal oxides and more exposed acid sites were achieved on the catalyst 10Zn1Ce5-AS with the presence of organic template in SBA-15 during the solid-state grinding process. The catalytic performance was evaluated in a fixed-bed reactor and a 1,3-butadiene selectivity of as high as 45% is achieved. This is attributed to the coupling effect of Zn and Ce species in the mesopores of SBA-15, in which Zn promotes ethanol dehydrogenation and Ce enhances aldol-condensation, respectively. Additionally, solvent-free method inspires new catalyst synthesis strategy for the production of 1,3-butadiene from ethanol.

High aspect ratio Ca6Si6O17(OH)2 nanowires: Green hydrothermal synthesis, formation mechanism, optical and photoluminescence properties

Calcium silicate 1D nanostructures have aroused widespread concern and become widely available for drug delivery, and photoluminescence host, etc., which however have traditionally been synthesized via high temperature based molten salt synthesis or solution-based techniques, in the presence of organic template or solvents. Herein, a facile controllable green hydrothermal route (200 °C, 12.0 h) to uniform high aspect ratio high purity Ca6Si6O17(OH)2 nanowires (diameter: 20.0–120.0 nm, aspect ratio: 60.0–350.0) has been developed for the first time by using abundant CaCl2·2H2O and Na2SiO3·9H2O as raw materials, in the absence of any organic stabilizer, template, or directing agent. Effects of process parameters such as molar ratio of reactants, reaction time, temperature, reactant concentration, and dropping rate on the hydrothermal products were investigated in detail, and an intrinsic highly anisotropic structure induced hydrothermal formation mechanism of the high aspect ratio Ca6Si6O17(OH)2 nanowires was proposed. The Ca6Si6O17(OH)2 nanowires exhibited a transparent characteristic from the ultraviolet to visible range, and the Ca6Si6O17(OH)2:1.2%Tb3+ nanophosphors demonstrated the strongest photoluminescence emission intensity. With the doping molar percentage of Tb3+ changing from 0.5% to 1.5%, the quantum yields (QYs) varied within the range of 43%–72%, definitely suggesting the Ca6Si6O17(OH)2 nanowires as a great promising host candidate for green-emitting luminescent materials in light display systems, and optoelectronic devices, etc.

Hydrogenation of methyl acetate to ethanol by Cu/ZnO catalyst encapsulated in SBA‐15

The hydrogenation of methyl acetate (MA) is one of the important key processes for synthesis of ethanol from syngas. This work reports a highly efficient Cu‐ZnO/SBA‐15 catalyst prepared by facile solid‐state grinding method. Both copper and zinc species were encapsulated in SBA‐15 in high dispersion with the presence of organic template. The mixed homogeneity and interaction between copper and zinc species was enhanced as well with the help of organic template, resulting in the formation of Cu+ species in the reduced catalysts. Moreover, TOFCu(0) linearly increased with the Cu+/Cu0 ratio, indicating that a high proportion of Cu+/Cu0 induced by ZnO should be a key prerequisite to achieve favorable hydrogenation performance. It seems that the Cu+ species originated from Cu‐ZnOx species are more active than that from Cu‐O‐Si species in the activation of MA. These results may provide an inspiration in rational design of Cu‐ZnO‐based catalysts for esters hydrogenation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2839–2849, 2017

ChemInform Abstract: Understanding Mechanism and Designing Strategies for Sustainable Synthesis of Zeolites: A Personal Story

AbstractReview: including organotemplate‐free synthesis, the design of environmetally friendly templates, and solvent‐free synthesis; 102 refs.

Understanding Mechanism and Designing Strategies for Sustainable Synthesis of Zeolites: A Personal Story.

Zeolites with intricate micropores have been widely studied for a long time as an important class of porous materials in different areas of industrial processes such as gas adsorption and separation, ion exchange, and shape-selective catalysis. However, their industrial syntheses are not sustainable, and normally require the presence of expensive organic templates and a large amount of solvents such as water. The presence of organic templates not only increases zeolite cost but also produces harmful gases during the removal of these templates by calcination, while the use of solvents significantly increases the amount of polluted water. This Personal Account briefly summarizes recent sustainable routes for the synthesis of zeolites in our group according to our understanding of the synthetic mechanism, and mainly focuses on the organotemplate-free synthesis of zeolites in the presence of zeolite seeds, the design of environmentally friendly templates, and solvent-free synthesis of zeolites.

Nanocrystalline zeolites in supercritical water. Part A: Opportunities and challenges for synthesis using organic templates

Nanocrystals of various zeolitic framework types, i.e. LTA, FAU, MFI, and ANA as well as smectite nanoclay (montmorillonite) with narrow size distribution and mean particle sizes smaller than 50nm have been synthesized rapidly in supercritical water (SC-H2O) medium by two approaches, namely, single and two-step procedures. The influence of the synthesis parameters on the particle size, shape and crystallinity was studied in a wide range of batch composition of reaction mixture, reactant sources, aging time, crystallization temperature and time in the presence of organic template. The samples were comprehensively characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma optical emission spectrometry (ICP-OES). The results suggest that contrary to the low temperature hydrothermal synthesis; there are strong competitions for the formation of different zeolites in SC-H2O. Hence, fine-tuning of all above-mentioned parameters is important to attain a pure product as desired. The aging time for induction step and establishment of initial nuclei, necessitate the aging time to be more than 24h at ambient temperatures in one-step process and 2h at 80°C in a two-step procedure. According to our results and previous studies of zeolite synthesis in hydrothermal method, a mechanism of zeolite formation in SC-H2O medium was suggested.

Incredible antibacterial activity of noble metal functionalized magnetic core–zeolitic shell nanostructures

Functionalized magnetic core–zeolitic shell nanostructures were prepared by hydrothermal and coprecipitation methods. The products were characterized by Vibrating Sample Magnetometer (VSM), X-ray powder diffraction (XRD), Fourier Transform Infrared (FTIR) spectra, nitrogen adsorption–desorption isotherms, and Transmission Electron Microscopy (TEM). The growth of mordenite nanoparticles on the surface of silica coated nickel ferrite nanoparticles in the presence of organic templates was also confirmed. Antibacterial activity of the prepared nanostructures was investigated by the inactivation of Escherichia coli as a gram negative bacterium. A new mechanism was proposed for inactivation of E. coli over the prepared samples. In addition, the Minimum Inhibitory Concentration (MIC) and reuse ability were studied. TEM images of the destroyed cell wall after the treatment time were performed to illustrate the inactivation mechanism. According to the experimental results, the core–shell nanostructures which were modified by organic agents and then functionalized with noble metal nanoparticles were the most active. The interaction of the noble metals with the organic components on the surface of nanostructures was studied theoretically and the obtained results were used to interpret the experimental results.

Syntheses and Structures of Uranyl Ethylenediphosphonates: From Layers to Elliptical Nanochannels

A family of uranium diphosphonates have been hydrothermally synthesized through the reaction of ethylenediphosphonic acid (EDP, H4L) and uranyl nitrate/zinc uranyl acetate in the presence of organic templates, such as tetraethyl ammonium (NEt4(+)), 4,4'-bipyridine (bipy), and 1,10-phenanthroline (phen). The UO2(2+) in UO2(H2O)(H2L)(EDP-U1) is equatorially five-coordinated by four phosphonate groups and one aqua ligand, forming a pentagonal bipyramid. Each EDP ligand is doubly protonated and chelates three UO2(2+), resulting in a layered structure. Compounds (NEt4)2(UO2)3(HL)2(H2L)·4H2O (EDP-U2) and (H2bipy)UO2L (EDP-U3) have the same layered structure in which NEt4(+) and protonated bipy fill in the uranyl-phosphonate interlayers, respectively, and play a role to balance the negative charges. Different from that in EDP-U1, the UO2(2+) exists in the form of a UO6 tetragonal bipyramid and is surrounded by four different EDP ligands in EDP-U2 and EDP-U3. (Hphen)2(UO2)2(H2L)3 (EDP-U4) features a three-dimensional framework structure with large elliptical channels along the c axis (1.3 × 1.1 nm(2)). Monoprotonated phen molecules fill in these channels and hold together through strong π···π interactions. All of the four compounds have been characterized by IR and photoluminescent spectroscopy. Their characteristic emissions have been attributed as transition properties of uranyl cations. The ion-exchange study indicates that [Co(en)3](3+) could partially replace the protonated phen molecules.

Removal of toxic heavy metal ions from waste water by functionalized magnetic core–zeolitic shell nanocomposites as adsorbents

Functionalized magnetic core-zeolitic shell nanocomposites were prepared via hydrothermal and precipitation methods. The products were characterized by vibrating sample magnetometer, X-ray powder diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, and transmission electron microscopy analysis. The growth of mordenite nanocrystals on the outer surface of silica-coated magnetic nanoparticles at the presence of organic templates was well approved. The removal performance and the selectivity of mixed metal ions (Pb(2+) and Cd(2+)) in aqueous solution were investigated via the sorption process. The batch method was employed to study the sorption kinetic, sorption isotherms, and pH effect. The removal mechanism of metal ions was done by chem-phys sorption and ion exchange processes through the zeolitic channels and pores. The experimental data were well fitted by the appropriate kinetic models. The sorption rate and sorption capacity of metal ions could be significantly improved by optimizing the parameter values.

Seed-directed synthesis of zeolites with enhanced performance in the absence of organic templates

We demonstrate here a seed-directed synthesis (SDS) of Beta, Levyne, and Heulandite zeolites in the absence of organotemplates, where the seeds drive crystallization of the zeolites. Compared with conventional Beta synthesized in the presence of organic templates, Beta-SDS exhibits large textural parameters, stable Al species, and unprecedentedly high density of active sites, resulting in superior catalytic activity and selectivity for valuable products in catalysis.

Feasibility of Pure Silica Zeolites

For an investigation of thermodynamic synthesis feasibility of pure silica zeolites, we applied computer simulations with two force fields BS and SLC. The recently developed BS force field excellently fits experimental enthalpies of pure silica zeolites with respect to quartz. On the basis of calculations with the BS force field, two empirical criteria may be adopted to assess thermodynamic feasibility. First, it was found that the upper energetic limit for synthesized pure silica zeolites is ca. 16 kJ/mol SiO2 above α-quartz and, second, the density of excess energy of pure silica zeolites lies in the region where ΔE/V < 0.5 kJ/cm3. We show how total energies and van der Waals, electrostatic, and three-body interactions correlate with the molar volume and topology of frameworks. The thermodynamic feasibility was not only studied from the structural viewpoint, but also the presence of organic templates and water was considered. We select a case study and propose a possible route for the synthesis of an MS...

Basic catalytic properties of as-synthesized molecular sieves

A series of as-synthesized molecular sieves have been tested and revealed useful as basic catalysts for Knoevenagel condensation under mild conditions. In order to understand the role of the Si/Al ratio, the structure, porosity and template agent, fifteen structures were synthesized and studied in this reaction. Siliceous and large pore molecular sieves showed high conversion levels (97%), while aluminum zeolites, even when containing large amount of organic material, showed distinct activity behavior, which was mainly dependent on the amount of framework silicon. This result, in addition to literature data, indicated that most likely siloxy anions ( SiO −) are the basic active sites. XPS measurements of these hybrid organic–inorganic catalysts showed that O1s binding energy is influenced by the presence of organic template, leading to the conclusion that they are interacting with framework oxygen, possibly balancing framework anions. Calcined siliceous molecular sieves, which had only silanol groups ( SiOH), showed negligible catalytic activity (lower than 2%). As-synthesized siliceous molecular sieves have proven to be useful for basic heterogeneous catalysis, particularly for the synthesis of fine chemicals or for catalytic processes demanding strong basic sites.

Organotemplate-Free and Fast Route for Synthesizing Beta Zeolite

Beta Zeolite has been widely used in industry, and its synthesis usually takes several days in the presence of organic templates. We demonstrate here an organotemplate-free and fast route for synthesizing Beta zeolite by addition of Beta seeds in the starting gel in the absence of any organic templates.

Synthesis of small crystals zeolite NaY

Zeolite NaY with small crystals was hydrothermally synthesized using a two-stage variable-temperature program without the presence of organic templates, structure-directing agent, seeding crystals and other additives. The as-synthesized samples were characterized by X-ray diffraction (XRD), laser particle size analyzer, scanning electron microscopy (SEM), and Fourier-Transformation Infrared (FT-IR) spectroscopy and Raman spectroscopy. The temperature was found to be a crucial factor for the control of the crystal size.

Partial substitution of the amine template by alkali metals (Rb, Cs) in the open-framework gallium phosphates ULM-3 and TREN-GaPO

The fluorinated gallium phosphates ULM-3 and TREN-GaPO were hydrothermally synthesized in the presence of organic templates (1,3-diaminopropane, dap, or tris(2-aminoethyl)amine, tren) and alkali metals (Rb, Cs). The solids were structurally characterized by single-crystal X-ray diffraction, and the structure examination indicates that the amine molecules are partially replaced by alkali cations. In ULM-3 (M δ [Ga 3(PO 4) 3(F,OH) 2], (1− δ/2)N 2C 3H 12, (1− δ/2)H 2O; M=Rb, Cs), the alkali metals are located within the 10-ring channels and partially occupy the positions of water and amine molecules ( δ≈0.07 for Rb and δ≈0.18 for Cs). In TREN-GaPO (M 0.5[Ga 3(PO 4) 3(F,OH) 2], 0.5N 4C 6H 21, H 2O; M=Rb, Cs), the alkali cations reside in the 8-ring channels, whereas the tren molecule is trapped within the 12-ring channels. The positions of rubidium and cesium atoms are compared with those of pyridine previously reported for TREN-GaPO.

Crystallization kinetics of zeolite ZSM-5

Zeolite ZSM-5 was synthesized from aluminosilicate gels in the presence of organic templates — tetrapropylammonium bromide (TPABr) and pyrrolidine (Py) — at temperatures of 423, 438 and 453 K. Nucleation and crystallization processes were subjected to a detailed kinetic analysis. The nucleation region is subdivided into two periods: induction and transition ones. Values of nucleation energy and crystallization energy, preexponential factor, rate of crystallization, and geometric factor have been calculated. Correlations between the estimated kinetic characteristics were found. The activation energy and the preexponential factor for the transitional and crystal-growth periods have the character of a kinetic compensation effect. The mechanism of the crystallization process is discussed on the basis of the kinetic features and correlations.

Quantitative monitoring of the crystallization of zeolite ZSM-5/ silicalite in non-alkaline media

The degree of crystallization of zeolite ZSM-5 and silicalite can be monitored quantitatively either by thermogravimetric analysis or by measuring the concentration of F − anions in the mother liquor; for silicalite there is moreover a good correlation between the degree of crystallinity as established by these techniques and X-ray diffraction crystallinity. The method is also applicable to the synthesis of other high-silica zeolites prepared in the presence of organic templates in non-alkaline fluoride media.

On the surface localization of enzymes in [formula omitted

Functionalized magnetic core–zeolitic shell nanostructures were prepared by hydrothermal and coprecipitation methods. The products were characterized by Vibrating Sample Magnetometer (VSM), X-ray powder diffraction (XRD), Fourier Transform Infrared (FTIR) spectra, nitrogen adsorption–desorption isotherms, and Transmission Electron Microscopy (TEM). The growth of mordenite nanoparticles on the surface of silica coated nickel ferrite nanoparticles in the presence of organic templates was also confirmed. Antibacterial activity of the prepared nanostructures was investigated by the inactivation of Escherichia coli as a gram negative bacterium. A new mechanism was proposed for inactivation of E. coli over the prepared samples. In addition, the Minimum Inhibitory Concentration (MIC) and reuse ability were studied. TEM images of the destroyed cell wall after the treatment time were performed to illustrate the inactivation mechanism. According to the experimental results, the core–shell nanostructures which were modified by organic agents and then functionalized with noble metal nanoparticles were the most active. The interaction of the noble metals with the organic components on the surface of nanostructures was studied theoretically and the obtained results were used to interpret the experimental results.