Synthesis of NaA zeolite membrane by microwave heating

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support by microwave heating (MH) was investigated. The formation of a NaA zeolite membrane was drastically promoted by MH. The synthesis time was reduced from 3 h for conventional heating (CH) to 15 min for MH. Surface seeding cannot only promote the formation of NaA zeolite on the support, but also inhibit the transformation of NaA zeolite into other types of zeolites. The thickness of the NaA zeolite membrane synthesized by MH was about 4 mum, thinner than that of NaA zeolite membrane synthesized by CH. The permeance of NaA zeolite membrane synthesized by MH was four times higher than that of the NaA zeolite membrane synthesized by CH, while their permselectivities were comparable. Multi-stage synthesis resulted in the transformation of NaA zeolite into other types of zeolites, and the perfection of the as-synthesized membrane decreased.

Synthesis of zeolite NaA membranes with high permeance under microwave radiation on mesoporous-layer-modified macroporous substrates for gas separation

This article reported the NaA zeolite membranes with high permeance synthesized with microwave heating method under different conditions: (1) on a macroporous substrate in gel, (11) on a mesoporous/macroporous (top-mesoporous-layer-modified macroporous) substrate in gel, and (111) on a mesoporous/macroporous substrate in sol. In general, the H-2 permeance of the NaA membranes by microwave heating in gel was usually at the level of 10(-6) mol s(-1) m(-2) Pa-1, much higher than that by the conventional hydrothermal synthesis. At similar H-2/C3H8 permselectivity. On the substrate modified mesoporous top layer, the H-2 permeance of the NaA membranes by microwave heating in gel or sol was further enhanced, while maintaining comparable H-2/C3H8 permselectivity, due to the prevention of penetration of the reagent into the pores of the macroporous substrate. Meanwhile, the synthesis took less time in sol than in gel on the mesoporous/macroporous substrate. The NaA membranes synthesized in sol had larger permeance than those in gel and underwent transformation in shorter time. The permeation of C3H8 suggested that there existed unwanted intercrystalline pores or defects in the membranes. © 2005 Elsevier B.V. All rights reserved.

Optimised microwave-assisted synthesis of methylcarbonate salts: a convenient methodology to prepare intermediates for ionic liquid libraries

The reaction of 1-butylpyrrolidine with dimethyl carbonate to yield the ionic liquid precursor, 1-butyl-1-methylpyrrolidinium methylcarbonate, has been investigated under microwave heating conditions and the reaction parameters optimised to achieve 100% yield of the pyrrolidinium salt with no by-products in under 1 h. The reactions of tributylamine, trioctylphosphine, and 1-butylimidazole with dimethyl carbonate under comparable conditions have also been evaluated, yielding the corresponding methylcarbonate salts which can be used as intermediates for the preparation of halide-free ionic liquids without generating any undesirable salt wastes.

Microwave Irradiation for the Facile Synthesis of Transition-Metal Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal-Carbonyl Precursors and Ru-, Rh-, and Ir-NP/IL Dispersions as Biphasic Liquid-Liquid Hydrogenation Nanocatalysts for Cyclohexene

Stable chromium, molybdenum, tungsten, manganese, rhenium, ruthenium, osmium, cobalt, rhodium, and iridium metal nanoparticles (MNPs) have been reproducibly obtained by facile, rapid (3 min), and energysaving 10 W microwave irradiation (MWI) under an argon atmosphere from their metal–carbonyl precursors [Mx(CO)y] in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]). This MWI synthesis is compared to UV-photolytic (1000 W, 15 min) or conventional thermal decomposition (180–2508C, 6–12 h) of [Mx(CO)y] in ILs. The MWIobtained nanoparticles have a very small (<5 nm) and uniform size and are prepared without any additional stabilizers or capping molecules as long-term stable M-NP/IL dispersions (characterization by transmission electron microscopy (TEM), transmission electron diffraction (TED), and dynamic light scattering (DLS)). The ruthenium, rhodium, or iridium nanoparticle/IL dispersions are highly active
and easily recyclable catalysts for the biphasic liquid–liquid hydrogenation of cyclohexene to cyclohexane with activities of up to 522 (mol product)(mol Ru)1h1 and 884 (mol product)(molRh)1h1 and give almost quantitative conversion within 2 h at 10 bar H2 and 908C. Catalyst poisoning experiments with CS2 (0.05 equiv per Ru) suggest a heterogeneous surface catalysis of RuNPs.

Microwave-assisted Cu-catalyzed Ullmann ether synthesis in a continuous-flow milli-plant

The combination of milli-scale processing and microwave heating has been investigated for the Cu-catalyzed Ullmann etherification in fine-chemical synthesis, providing improved catalytic activity and selective catalyst heating. Wall-coated and fixed-bed milli-reactors were designed and applied in the Cu-catalyzed Ullmann-type CO coupling of phenol and 4-chloropyridine. In a batch reactor the results show clearly increased yields for the microwave heated process at low microwave powers, whereas high powers and catalyst loadings reduced the benefits of microwave heating. Slightly higher yields were found in the Cu/ZnO wall-coated as compared to the Cu/TiO fixed-bed flow-reactor. The benefit here is that the reaction occurs at the surface of the metal nanoparticles confined within a support film making the nano-copper equally accessible. Catalyst deactivation was mainly caused by Cu oxidation and coke formation; however, at longer process times leaching played a significant role. Catalyst activity could partially be recovered by removal of deposited by-product by means of calcination. After 6h on-stream the reactor productivities were 28.3 and 55.1kgprod/(mR3h) for the fresh Cu/ZnO wall-coated and Cu/TiO fixed-bed reactor, respectively. Comparison of single- and multimode microwaves showed a threefold yield increase for single-mode microwaves. Control of nanoparticles size and loading allows to avoid high temperatures in a single-mode microwave field and provides a novel solution to a major problem for combining metal catalysis and microwave heating. Catalyst stability appeared to be more important and provided twofold yield increase for the CuZn/TiO catalyst as compared to the Cu/TiO catalyst due to stabilized copper by preferential oxidation of the zinc. For this catalyst a threefold yield increase was observed in single-mode microwaves which, to the best of our knowledge, led to a not yet reported productivity of 172kgprod/(mR3h) for the microwave and flow Ullmann CO coupling. © 2012 Elsevier B.V.

Ionothermal, microwave-assisted synthesis of indium(III) selenide

Microcrystalline indium(III) selenide was prepared from a diphenyl diselenide precursor and a range of chloroindate(III) ionic liquids via a microwave-assisted ionothermal route; this is the first report on the use of either microwave irradiation or ionic liquids to prepare this material. The influence of the reaction temperature, dilution with a spectator ionic liquid and variation of the cation and the anion of the ionic liquid on the product morphology and composition were investigated. This resulted in a time-efficient and facile one-pot reaction to produce microcrystalline indium(III) selenide. The product formation in the ionic liquids has been monitored using Raman spectroscopy. The products have been characterised using PXRD, SEM and EDX. Advantages of this new route, such as the ease of solubilisation of all reactants into one phase at high concentration, the negligible vapour pressure irrespective of the reaction temperature, very fast reaction times, ease of potential scale-up and reproducibility are discussed.

Zinc selenide nano- and microspheres via microwave-assisted ionothermal synthesis

Zinc selenide nanospheres were prepared from a diphenyl diselenide precursor and a range of chloro- and bromozincate(II) ionic liquids via a microwave-assisted ionothermal route; this is the first report on the use of microwave irradiation in combination with ionic liquids to prepare this material. The method is a time-efficient and a facile one-pot reaction to produce zinc(II) selenide nanomaterials. The product formation in the ionic liquids has been monitored using Raman spectroscopy. The products have been characterised using PXRD, SEM, EDX, photoluminescence and UV-VIS spectroscopy. Advantages of this new route, such as ease of solubilisation of all reactants into one phase at high concentration, the negligible vapour pressure irrespective of the reaction temperature, very fast reaction times, ease of potential scale-up and reproducibility are discussed.

Synthesis, Characterisation and Properties of (Ba1-xSrx) (Nd1/2Nb1/2 ) 03 Ceramics for Application as Dielectric Resonators in Microwave Circuits

The (Ba1-x Srx) (Nd1/2, Nb1/2) O3 ceramics have been prepared by the conventional ceramic route for different values of x. Addition of a small amount of CeO2(1 wt%) as a sintering aid increased the density of the samples. The structure and microstructure of the sintered samples are studied by X-ray diffraction and SEM methods. The dielectric properties of the samples are measured in the microwave frequency region as a function of composition. The dielectric constant decreases as x increases. The coefficient of thermal variation of resonant frequency decreases as the Sr content increases and goes to the negative side. The dielectric properties of (Ba1-x Srx) (Nd1/2, Nb1/2) O3 are in the range suitable for application as dielectric resonators in microwave circuits

Synthesis, Characterization and Properties of Ca5A2TiO12 (A=Nb, Ta) Ceramic Dielectric Materials for Applications in Microwave Telecommunication Systems

Microwave ceramic dielectric materials Ca5Nb2TiO12 and Ca5Ta2TiO12 have been prepared by a conventional solid-state ceramic process. The structure was studied by X-ray diffraction and the dielectric properties were characterized at microwave frequencies. The ceramics posses a relatively high dielectric constant, very low dielectric loss (Q5 x f > 30000GHz) and small temperature variation of resonant frequency. These materials are potential candidates for dielectric resonator applications in microwave integrated circuits. [DOI: 10. 1 143/JJAP.41.3834]

A facile and single pot strategy for the synthesis of novel naphthyridine derivatives under microwave irradiation conditions using ZnCl2 as catalyst, evaluation of AChE inhibitory activity, and molecular modeling studies

A series of novel naphthyridine derivatives 3 and 4 was prepared from substituted pyridine 2 and ketones using ZnCl2 as catalyst under microwave irradiation conditions. All the compounds were evaluated for AChE inhibitory activity and promising compounds 3d, 3e, 4b, and 4g was identified. Representative compounds 3d and 3e were found to show insignificant THLE-2 liver cell viability/toxicity. The binding mode between X-ray crystal structure of human AChE and compounds was studied using molecular docking method and fitness scores were found to be in good correlation with the activity data.

Microwave-assisted hydrogel synthesis: a new method for crosslinking polymers in aqueous solutions

It has been found that hydrogels may be formed by microwave irradiation of aqueous solutions containing appropriate combinations of polymers. This new method of hydrogel synthesis yields sterile hydrogels without the use of monomers, eliminating the need for the removal of unreacted species from the final product. Results for two particularly successful combinations, poly(vinyl alcohol) with either poly(acrylic acid) or poly(methylvinylether-alt-maleic anhydride), are presented. Irradiation using temperatures of 100–150 °C was found to yield hydrogels with large equilibrium swelling degrees of 500–1000 g g−1. Material leached from both types of hydrogel shows little cytotoxicity towards HT29 cells.