Presence Of Structure-directing Agent Research Articles

Synthesis of ferrierite-type zeolite by microwave method using ethylenediamine as an organic structure-directing agent

A new method for the synthesis of ferrierite-type zeolite has been developed using microwave irradiation in the presence of structure-directing agents (templates). The physicochemical characteristics of the synthesized zeolites were investigated by X-ray diffraction analysis, low-temperature nitrogen adsorption–desorption and SEM-EDX. When comparing the synthesis products, it was found that microwave irradiation significantly reduces the crystallization time of the synthesized zeolites compared to traditional hydrothermal treatment

The relative stability of SCM-14 germanosilicate with different distributions of germanium ions in the absence and presence of structure-directing agents

According to periodic DFT calculations suggest that: Ge atoms in SCM-14 germanosilicate are clustered forming D4Rs populated entirely by Ge; structures with more Ge–O–Ge bridges are more stable; simulated19F NMR chemical shifts do not correlated with Ge content of the D4R.

Fabricating ZSM-23 with reduced aspect ratio through ball-milling and recrystallization: Synthesis, structure and catalytic performance in N-heptane hydroisomerization

Unidimensional zeolites often form rod-shaped crystals that suffer from low catalytic selectivity or catalyst lifetime owing to their poor diffusion properties. Combined postsynthetic ball-milling and recrystallization methods were investigated to produce unidimensional ZSM-23 crystals with reduced aspect ratio. The influences of ball-milling in the presence/absence of structure directing agent (SDA) and diverse recrystallization media, including H2O, Na2Si3O7 solution, synthetic mixture and mother liquor, over crystallinity, crystal size, textural properties as well as acidity, were intensively explored using characterization techniques such as XRD, SEM, N2 physisorption, 27Al MAS NMR, NH3-TPD, pyridine IR spectroscopy and diffusion measurement. The results showed that crystal size of ZSM-23 was considerably reduced after ball-milling treatment, however, at the expense of crystallinity, acidity and porosity. Recrystallization in the presence of mother liquor was identified as the most effective and economic way to restore crystallinity. The optimized ZSM-23-M-m sample derived from ball-milling in the presence of SDA and a subsequent recrystallization in separated synthesis mother liquor exhibited higher isomer yield (ca. 53%) than the parent sample (ca. 34%) in n-heptane hydroisomerization reaction owing to the enhanced diffusion property and regained acidity after recrystallization.

Antireflective mesoporous silica coatings by optimization of water content in acid-catalyzed sol-gel method for application in glass covers of concentrated photovoltaic modules

Porous silica layers with outstanding antireflective properties have been prepared by acid-catalyzed sol-gel process in presence of organic phases as structure directing agents (SDA) and excess water, with the aim of offering a cost-competitive, easy up-scaling and high efficiency process that contributes to reduce current levelized cost of energy (LCOE) of concentrating photovoltaics (CPV). The process has been optimized by controlling the water/alkoxide ratio, which is an important structure-regulating tool, having a strong influence in the structural properties of sol-gel synthesized materials. Hydrolysis of the inorganic precursor has been accomplished in high water/alkoxide conditions and in the presence of SDAs. Evaporation induced self-assembly (EISA) during coating deposition and the scanning of four types of SDAs have permitted to select the coating that fulfilled specific thickness and refractive index values with, in parallel, excellent results on sol stability. The final optimization has produced mesoporous coatings with ∼9 nm mean pore size, leading to an enhancement in transmittance up to 7.4% over bare glass in the 300–1500 nm wavelength range. The transmittance spectra have been used as inputs for the theoretical calculation of the short-circuit current density of a commercially available multijunction solar cell for CPV applications.

Synthesis of Trigonal Mo–V–M3rd–O (M3rd = Fe, W) Catalysts by Using Structure-Directing Agent and Catalytic Performances for Selective Oxidation of Ethane

Crystalline Mo–V–M3rd–O (M3rd = Fe, W) catalysts (MoVFeO and MoVWO) with trigonal symmetry were successfully obtained by a hydrothermal method in the presence of structure-directing agents (ammonium cation and ethylammonium cation) and their catalytic performances for selective oxidation of ethane were compared with trigonal Mo3VOx catalyst (MoVO). Fe and W were uniformly distributed throughout the rod-shaped crystals. XRD, Raman, XRD simulation, and Rietveld analysis revealed that MoVFeO contained Fe in a heptagonal channel and W in MoVWO substituted Mo in {Mo6O21}6− pentagonal unit in the structure. MoVWO catalyst showed comparable catalytic activity with MoVO for the selective oxidation of ethane. On the other hand, catalytic performance of MoVFeO was far less compared with those of MoVO and MoVWO. The picture that the catalytic reaction occurs at the specific part in the structure could be visualized.

Controlled synthesis of ZnO spheres using structure directing agents

Controlled liquid phase deposition has been developed for fabricating zinc oxide (ZnO) nano/microspheres using a mixture of precursor solution of zinc acetate dihydrate, ammonium hydroxide, and structure directing agents (SDAs) such as ethanol and urea. We found that ZnO spheres can be formed when the SDAs are optimized with the proper pH values. At pH values less than 12, an anisotropic growth of ZnO flowers and rod structures was produced with/without SDAs. On the contrary, at a pH value of 12 the directional growth of ZnO was absolutely controlled and an isotropic growth of ZnO spheres was developed with the presence of SDAs. We also found that the volume ratio of ethanol and urea in the solution was a key factor to modulate the uniform size distribution and diameter of the ZnO spheres from nanometer to micrometer range.

Synthesis of a hierarchically micro–macroporous structured zeolite monolith by ice-templating

The zeolite monolith with a micrometre-sized honeycomb structure was prepared by using the ice-templating method. The synthesized samples were characterized by SEM, powder X-ray diffraction analysis, mercury porosimetry, and nitrogen adsorption–desorption measurements. The precursor silica gels with channel diameters of 10–50 µm were prepared by the ice-templating method. Then the amorphous phase of the precursor silica gels was converted into a crystalline phase by the steam treatment in the presence of structure-directing agents. In this work, tetrapropyl ammonium hydroxide was selected as a structure-directing agent, and the crystalline phase of the synthesized sample was identified as silicalite-1 from XRD analysis. After crystallization, the particulate silicalite crystals were generated on the surface of the honeycomb wall, and the honeycomb structure was retained without cracking. The size of the synthesized silicalite crystals was controlled by the crystallization temperature and time. The nitrogen adsorption–desorption isotherm on the synthesized silicalite monolith showed type I isotherms, and the specific surface area calculated by the Brunauer–Emmett–Teller method was 332.0 m2 g−1. These results indicated the existence of micropores in the framework of silicalite-1.

NF/RO faujasite zeolite membrane-ammonia absorption solvent hybrid system for potential post-combustion CO 2 capture application

A novel concept regarding nanofiltration/reverse osmosis (NF/RO) membrane–ammonia absorption solvent hybrid process for potential application to post-combustion CO 2 capture was developed and proven experimentally, in which the synthesis of selective membranes was investigated in detail. For this purpose, FAU-type zeolite membranes prepared with and without TMAOH by secondary growth method were selected for NF/RO reclamation of ammonia water and water components from 2 carbon-rich electrolyte solutions (0.15 and 0.56 M total carbon loadings) close in chemical composition to aqueous ammonia based post-combustion CO 2 scrubbing solution. It was found that the incorporation of TMAOH as an structure-directing agent (SDA) into the synthetic gel precursors leads to the formation of FAU membranes with superior separation performances to those prepared without SDA. Without SDA, the resulting membranes were severely contaminated with the byproduct Na-P1 zeolites. This study further demonstrates that neither ion exchange nor calcination step is necessary to remove the occluded SDA, without trading off the permeation fluxes of FAU zeolite membranes. In the presence of SDA, both morphology and crystallinity of the membranes are strongly dependent upon the basicity of the synthetic gel, and have an important effect on the NF/RO separation performances of the obtained membranes. The physicochemical properties of these zeolite membranes were characterized by a series of techniques including X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescent spectroscopy (XRF).

Hydrothermal synthesis and characterization of two novel three-dimensional vanadium phosphites: |(C 10H 10N 2)| [formula omitted] and |(C 4H 16N 3)| [formula omitted

Two novel three-dimensional vanadium phosphites |(C 10H 10N 2)| V 2 IV O 2 ( HPO 3 ) 2 ( H 2 PO 3 ) 2 1 and |(C 4H 16N 3)| V 2 IV V III O 2 F 2 ( HPO 3 ) 4 2 have been synthesized hydrothermally in the presence of structure-directing agents. Single-crystal structural analysis reveals that compound 1 has a three-dimensional open-framework with two different types of intersecting channels (monoclinic, P2 1/ n, a = 6.3541(14) Å, b = 10.460(2) Å, c = 14.769(3) Å, β = 90.412(5) o, V = 981.6(4) Å 3, Z = 2 with R 1 = 0.0523), while compound 2 (orthorhombic, Pbca, a = 13.612(3) Å, b = 9.5753(19) Å, c = 14.022(3) Å, V = 1827.6(6) Å 3, Z = 4 with R 1 = 0.0441) presents a three-dimensional open-framework that consists of a novel {V 3O 14F 2} trimer with mixed valence V 2 IV V III linked by two bridging F atoms. In addition, it is worth noting that the organic templates play important roles in the formation of both novel structures. Further characterization of the two compounds has been performed, including X-ray powder diffraction, ICP, CHN, IR and TG–DTA analyses.

Synthesis, Characterizations and Spectral Properties of a New One‐Dimensional Organically Templated Zincophosphite.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Molecular chemistry and nanosciences: on the way to interactive materials

This article is focused on mesoporous hybrid organic–inorganic materials prepared in the presence of structure-directing agents. We attempt to show that they are currently the best supports for exploring polyfunctional materials, which can provide a route to interactive materials. We define interactive materials as nanomaterials of which two properties are in a position to interact with one another. For the purpose of constructing such materials, we describe the functionalization of the channel pores of ordered mesoporous silica, the silica framework and the functionalisation of both, either successively or simultaneously. This last route could allow the preparation of materials coupling two physical properties, located on the nanometric range—one in the channel pores and the other in the silica framework—which could present unexpected interactions. This approach requires a mastery of the chemistry for the preparation of the appropriate precursors as well as of the structure.

Synthesis, characterizations and spectral properties of a new one-dimensional organically templated zincophosphite

A new one-dimensional zincophosphite, (C 2H 10N 2)[Zn(HPO 3) 2], has been synthesized under mild hydrothermal conditions in the presence of structure-directing agent, ethylenediamine, and its crystal structure was determined by single-crystal X-ray diffraction method (monoclinic, C2/ c, a = 13.921(4) Å, b = 7.7301(19) Å, c = 8.858(2) Å, β = 91.224(3)°, V = 953.0(4) Å 3, Z = 4). The crystal structure of the title compound is characterized by corner-sharing ZnO 4 and HPO 3 tetrahedra, leading to infinite corner-shared four-membered ring chains. Diprotonated ethylenediamine ions occupying the interspaces interconnect the chains via hydrogen bonds to form a novel organic–inorganic layered-like stack. Luminescent measurement of the title compound shows a broad emission band between 350 and 500 nm when excited with 340 nm UV light.

Synthesis of [Al]-SSZ-31 Molecular Sieves Using [Al]-Beta Zeolite ([Al]-BEA) as Precursors

Abstract The aluminosilicate version of SSZ-31 ([Al]-SSZ-31) zeolite was synthesized by a new route including phase-transformation, wherein an aluminosilicate analog of beta zeolite ([Al]-BEA) was used as a precursor and 1,1,1,8,8,8-hexaethyl-1,8-diazoniaoctane dihydroxide was used as a structure-directing agent (SDA). [Al]-BEA precursors synthesized by two routes, viz. the hydrothermal (HTS) and dry-gel conversion (DGC) method, were employed for the synthesis. [Al]-SSZ-31 with a low output SiO2/Al2O3 ratio crystallized only when the precursor (SiO2/Al2O3 = 30), prepared by DGC method, was employed. Precursors synthesized by the HTS method produced highly crystalline samples, however, only in the high silica region. In general, [Al]-SSZ-31 samples over a wide range of SiO2/Al2O3 ratios could be synthesized using a precursor route. During crystallization, a phase transformation from [Al]-BEA to [Al]-SSZ-31 was observed, indicating dissolution of the beta phase, followed by its redirection towards the SSZ-31 phase in the presence of SDA. An increase in gel water helped to produce pure [Al]-SSZ-31. [Al]-SSZ-31 was found to crystallize in NaOH/SiO2 window of 0.040–0.056. Scanning electron microscopy (SEM) showed plate-like crystals of about 5 μm in size. 13C CP MAS NMR indicated that the SDA was intact inside the pores during crystallization. Furthermore, the samples were also characterized by 29Si and 27Al MAS NMR in addition to X-ray diffraction (XRD), temperature-programmed desorption of ammonia (NH3-TPD), SEM, etc.