Remarkable effect of addition of In and Pb on the reduction of N2O by CO over SiO2 supported Pd catalysts

The effect of addition of In and Pb on the reduction of N₂O by CO was studied over SiO₂ supported Pd catalysts, using a closed gas circulation system as well as in-situ infrared spectroscopy. Formation of intermetallic compounds such as Pd_0.48In_0.52, Pd₃Pb and Pd₃Pb₂ was observed which caused a drastic enhancement of the rate of N₂ formation. The infrared spectroscopic analyses revealed a weakening of the adsorption strength of CO on Pd metal by the formation of intermetallic compounds, which is likely the main reason for the enhancement of the reaction rate. From a kinetic investigation as well as in situ FT-IR observation during the N₂O-CO reaction, a redox mechanism was proposed involving the oxidation of the surface by N₂O followed by its reduction by CO. Over Pd/SiO₂, the former process seems to be the rate limiting step because of the inhibition of N₂O activation by strongly adsorbed CO. By adding In or Pb, the rate limiting step shifted to the latter process, which resulted in a large enhancement in the rate of N₂ formation.     

Magnetically separable Fe3O4/graphene oxide nanocomposite: An efficient heterogenous catalyst for spirooxindole derivatives synthesis

Heterocyclic compounds such as spirooxindole, with five rings containing nitrogen, have an important role in the realm of medicine. This study aims to synthesize the spirooxindole derivative compounds using Fe₃O₄/graphene oxide (GO) nanocomposite as the catalyst. The GO sample was synthesized by Hummers' method, followed by the insertion of Fe₃O₄ into the graphene oxide layers by the co-precipitation method. Both XRD and FTIR analyses reveal that GO and Fe₃O₄/GO samples have been successfully formed. SEM-EDX micrograph supported by TEM image indicates that the Fe₃O₄ nanoparticles in the composite have excellent dispersibility, attributable to the existence of the GO sheets. The evaluation of the ability of Fe₃O₄/GO as a catalyst in the synthesis of spirooxindole derivatives was carried out by the one-pot three-component method. The reaction yield shows that Fe₃O₄/GO was a suitable and reusable catalyst in this reaction.     

Hollow fiber supported liquid membrane process for the separation of NH3 from aqueous media containing NH3 and CO2

A hollow fiber supported liquid membrane (SLM) process was investigated experimentally and theoretically for the separation of NH₃ from aqueous solutions containing NH₃ and CO₂. DTPA and D2EHPA were used as carriers and n-decanol was used as a diluent in this process. The membrane stripping experiments, as well as the extractive equilibrium experiments, indicate that DTPA is a better carrier than D2EHPA in relation to the increase in the NH₃ stripping rate. The influence of operating conditions, such as flow rate, the ratio of NH₃ to CO₂, and carrier concentration, on the membrane stripping rate were examined. The experimental data demonstrate that the NH₃ stripping rate by an SLM process is not significantly influenced by the amount of CO₂ present, as is that by the supported gas membrane. To predict the stripping of NH₃ from solutions containing NH₃ and CO₂, a mathematical model incorporating chemical equilibria and Nernst–Planck diffusion was developed to describe the mass transport. The experimental data suggested that the SLM process can effectively strip NH₃ from aqueous solutions containing NH₃ and CO₂.     

Investigation into the formation of phases with a Ba<Subscript>2</Subscript>Ti<Subscript>9</Subscript>O<Subscript>20</Subscript>-type structure in the BaO-TiO<Subscript>2</Subscript> and BaO-SrO-TiO<Subscript>2</Subscript> systems

The mechanism of formation of barium titanate Ba₂Ti₉O₂₀ in the BaO-TiO₂ and BaO-SrO-TiO₂ systems is investigated using initial mixtures prepared by three methods, namely, mechanical grinding of the initial reactants, coprecipitation from aqueous solutions of salts, and the sol-gel technique. It is established that, irrespective of the preparation procedure, the formation of Ba₂Ti₉O₂₀ proceeds through the formation of the intermediate phases BaTi₄O₉ and BaTi₅O₁₁. The nature of the intermediate phases is determined by the homogeneity and dispersion of the initial mixture, as well as by the stability of the intermediate phase. The most optimum conditions for the synthesis of Ba₂Ti₉O₂₀ are provided by the formation of BaTi₅O₁₁ as an intermediate phase upon heat treatment of the coprecipitation products in the nanocrystalline state. The metastability and structural defects in the BaTi₅O₁₁ intermediate phase encourage a decrease in the temperature of the final heat treatment by 100–150°C in the course of the preparation of Ba₂Ti₉O₂₀ single-phase ceramics.     

Durability and performance of CGO barriers and LSCF cathode deposited by spray-pyrolysis

Ce_0.9Gd_0.1O_1.95 (CGO) protective layers are prepared by two different methods to prevent the reaction between the Zr_0.84Y_0.16O_1.92 (YSZ) electrolyte and the La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode. In the first method, the CGO layers are deposited by an airbrushing technique from an ink containing CGO particles without and with cobalt as sintering aids. The second strategy consists in preparing both a dense CGO barrier layer and a porous LSCF cathode by spray-pyrolysis deposition, in order to further reduce the fabrication temperature and minimize the reaction between the cell components. The samples prepared by spray-pyrolysis exhibit better performance and durability than those obtained by conventional sintering methods. The results suggest that the interfacial reactivity between YSZ and LSCF as well as the Sr-enrichment at the cathode surface can be avoided by using low-temperature fabrication methods and by operating at temperatures lower than 650?°C.     

Modelling of NOx adsorption over NOx adsorbers

Modelling of the phenomena involved during the adsorption of NO_x on NO_x trap catalysts was developed. The aim of the model is the prediction of the quantity of stocked barium nitrate as well as the emissions of NO and NO₂, as a function of time and temperature. The mechanism of the process is sounded on the adsorption of gas species (NO, NO₂, O₂) on platinum sites, equilibrium reaction between adsorbed species followed by the formation of Ba(NO₃)₂. This formation of barium nitrate is limited by the thermal decomposition reaction which liberates NO in the gas phase. The kinetic constant of decomposition of barium nitrate was determined by temperature programmed thermogravimetry on pure Ba(NO₃)₂, using the method of Freeman and Carroll. Other kinetic constants bound to the mechanism were estimated by fitting the results of the model to experimental results.The mechanism was validated for various values of the molar fraction of O₂, the molar fraction of NO and various values of the NO/NO₂ ratio in the gas entering the reactor. It was also tested with different catalyst compositions (variation of the platinum and BaO concentrations). The importance of oxygen in the process was clearly demonstrated as well as the promoting role of NO₂.     

Chemoselective transfer hydrogenation reactions over nanosized γ-Fe2O3 catalyst prepared by novel combustion route

γ-Fe₂O₃ catalyst was prepared by the novel combustion route. The as synthesized catalyst was characterized by several analytical techniques such as XRD, SEM, TG-DTA, etc. Chemoselective reduction of nitro compounds was studied over γ-Fe₂O₃ using propan-2-ol as a hydrogen donor and KOH promotor in liquid phase reaction. The catalyst used for this synthetically useful transformation showed good activity.     

Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low Temperature

Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C₂ selectivity as well as the methane conversion are functions of methane‐to‐oxygen ratio, gas residence time, and electric current. At CH₄/O₂ ratio of 5 and the residence time of about 30 ms, a C₂ yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO₂ with CO/CO₂ ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C₂ products are produced by a consecutive mechanism, whereas CO_x is formed during parallel reactions.     

Manganese ferrite-polyaniline hybrid materials: Electrical and magnetic properties

Magnetic MnFe₂O₄ nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe₂O₄ using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe₂O₄ powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe₂O₄ powders and are higher by comparison to those of the MnFe₂O₄/PANI hybrid materials. The values of saturation magnetization in case of MnFe₂O₄ powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe₂O₄ powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe₂O₄ powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σ_DC = 54.5·10^?5S?m^?1) which was close to that of PANI (σ_DC = 61.2·10^?5 S?m^?1). The fact that the magnetic and electric properties of the synthesized MnFe₂O₄/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications.     

All-inorganic perovskite Cs4PbBr6 thin films in optoelectronic resistive switching memory devices with a logic application

Perovskite-based Cs₄PbBr₆ has potential applications in optoelectronic devices, such as photodetectors, electroluminescence devices and color converters. All-inorganic perovskite Cs₄PbBr₆ thin films were successfully prepared by a simple low-temperature synthesis method and were first implemented as an insulating layer in Au/Cs₄PbBr₆/PEDOT:PSS/Pt devices. The memory devices possess reproducible bipolar resistive switching behavior, low operating voltages, good endurance, and long retention times. Furthermore, the novel sandwich architecture enables the application of the Cs₄PbBr₆ films as memristors and photoresponsive behaviors. Considering the distinct photoresponses of the resistance state as a nonvolatile memory, the devices can be used as a logical "OR" gate by applying bias voltages and light illumination as input signals. The formation and annihilation of Br^- ion vacancy filaments induced by the external bias and light illumination can result in pronounced resistive switching performance. It is believed that solution-processed Cs₄PbBr₆-based devices have great potential for technological deployment at the forefront as a photonic nonvolatile memory as well as integrated modulating and arithmetic functions.     

A New Catalytic Transesterification for the Synthesis of Ethyl Methyl Carbonate

The application of a novel Ce_0.5Zr_0.5O₂ mixed oxide prepared by the microemulsion method as a support of Ru catalysts for the reforming of CH₄ with CO₂ originates a high-activity catalytic system with excellent stability under reaction conditions. The support characteristics clearly determine the catalytic stability of Ru catalysts under CH₄ + CO₂ reaction conditions. The introduction of cerium as a promoter in the ZrO₂ structure is shown to improve the catalyst performance by increasing the oxygen mobility in the support and consequently reducing deactivation by carbon deposition during reaction.     

A nonenzymatic hydrogen peroxide sensor based on Pt/PPy hollow hybrid microspheres

The surface of silica particles was NH₂? functionalized by 3‐aminopropyltrimethoxysilane, then the platinum/polypyrrole hybrid hollow microspheres were prepared by treating the SiO₂ template decorated by the H₂PtCl₆ via the NH₂? group with pyrrole vapor and developed as hydrogen peroxide (H₂O₂) sensor. The platinum/polypyrrole hybrid hollow sphere materials were characterized by transmission electron microscopy and infrared spectroscopy, and the catalytic electrodes were investigated by electrochemical method. The results showed that the nonenzymatic sensor displayed a good electro‐catalytic response and high sensitivity to the oxidation of H₂O₂, and the resulting sensor showed a wide linear range from 1.9 to 9.7 mM H₂O₂. The obvious response could be still observed in i–t curve when the concentration of H₂O₂ was as low as 1.0 μM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of Cr2O3 on the crystallization behavior of synthetic diopside and characterization of Cr-doped diopside glass ceramics

Diopside is the main crystalline phase in silicate materials such as ceramics and glass-ceramics. Herein, the effect of Cr₂O₃ on the microstructure and crystallization behavior of synthetic diopside, as well as the solubility of Cr₂O₃ in diopside is discussed. Samples were prepared by the melting method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and confocal laser scanning microscopy. Results show that the maximum achievable solubility of Cr₂O₃ in diopside is between 1% and 3% by weight, and that the magnesiachrome spinel formed by Cr₂O₃ can act as a nucleating agent for the diopside phase. Glass ceramics was prepared by synthesis slag which simulates the chromium-containing waste. The activation energy of crystallization is 274 KJ/mol and Avrami parameter is 3.23. The leaching behavior of glass ceramics was studied. Additionally, the effect of Cr₂O₃ on the mechanisms of phase change were discussed. The study provides a theoretical basis for the preparation of chromium containing waste-based silicate materials with diopside as the main crystalline phase.     

Preparation and characterization of magnetic star‐shaped amphiphilic copolymer nanoparticles of S‐Fe3O4‐PLA‐b‐MPEG

Magnetic star‐shaped amphiphilic copolymers (S‐Fe₃O₄‐PLA‐b‐MPEG) consisting of Fe₃O₄ as the core, poly(L ,D ‐lactide) (PLA) as the inner layer, and monomethyl polyethylene glycol (MPEG) as the out shell were synthesized. The syntheses included ring‐opening polymerization of L ,D ‐lactide initiated by hydroxyl modified Fe₃O₄ (Fe₃O₄‐(OH) _n), followed by the esterification of the PLA with MPEG. The structure of the star block copolymers were characterized by Fourier Transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy, nanoparticle size analyzer, and vibrating sample magnetometer. The nanoparticles in aqueous solution were made from the amphiphilic star copolymer. The average size of the nanoparticles was adjustable and increased with the increase of the PLA segments in the copolymer. The cytotoxicity grade of the nanoparticles was zero determined by the analysis of cytotoxicity. The nanoparticles could potentially be used as the drug vehicles for magnetic‐response controlled release. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

The crystalline quality of Si films prepared by thermal- and photo-CVD at low temperatures

Various silicon films were prepared by thermal- and UV photo-CVD processes. The reactants were SiH₄, Si₂H₆ SiH₂F₂, SiF₄, and H₂. Silicon films grown at temperatures below 500°C were either amorphous or crystalline depending on the process conditions, and the growth rates ranged between 5 and 80 Å/min. The film obtained by photo-CVD using fluoro-silanes as the reactants was crystalline even when the deposition temperature was. as low as 250°C. Analyses of the film by RBS, SIMS, XRD, andex-situ IR indicated that the film grown from silanes was contaminated by oxygen and other impurities while one from fluoro-silanes was relatively low in the impurities. The film crystallinity was higher in the latter case than the former.     

Synthesis and growth mechanism of donut-like lead titanate particles by hydrothermal method

Tetragonal perovskite structure PbTiO₃ donut-like particles have been synthesized by a hydrothermal method in strong alkaline environment using lead nitrate (Pb(NO₃)₂) as the lead source and TiCl₄ as the titanium source. The as-prepared particles were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), and it was indicated that the phase composition and particles shapes were influenced by the reaction temperature and reaction time. Based on the morphologies and phase evolutions as a function of reaction temperature or reaction time, a mechanism for the growth of the donut-like PbTiO₃ particles was proposed to involve nucleation, agglomeration, phase in situ conversion, dissolution, and recrystallization. The spherical particles were formed by primary nucleation of PbTi_0.8O_2.6 followed by agglomeration into platelets. Then, the platelet PbTi_0.8O_2.6 particles in situ converted into Pb₂Ti₂O₆ particles. Under the effects of temperature, pressure (autogenous pressure), and high solution pH value, the platelet Pb₂Ti₂O₆ particles dissolved from its center of surface and recrystallized to form PbTiO₃ nano-particles which adhered to its edges. Finally, the monocrystal donut-like PbTiO₃ particles were formed as the dissolution of Pb₂Ti₂O₆ particles completed.     

Facile one-step solid-state reaction route to synthesize ordered mesoporous β-Zn2SiO4–SiO2 nanocomposites

Ordered crystalline mesoporous β-Zn₂SiO₄–SiO₂ nanocomposites were prepared by one-step solid-state reaction using mesoporous silica as both template and silica source. Zinc oxide formed by decomposition of zinc nitrate reacts with mesoporous silica and the β-Zn₂SiO₄ forms and disperses inside the silica walls. The obtained β-Zn₂SiO₄–SiO₂ nanocomposites possess hexagonal mesostructure with the β-Zn₂SiO₄ weight percentage below 40%. The β-Zn₂SiO₄ nanocrystals are surrounded by the non-crystalline silica of mesoporous walls. The non-crystalline silica acting as a binder to stick β-Zn₂SiO₄ nanocrystals plays a role in restraining the phase transformation from β-Zn₂SiO₄ to α-Zn₂SiO₄ and increasing the thermal stability of mesoporous β-Zn₂SiO₄. The crystalline mesoporous β-Zn₂SiO₄ may be a potential candidate for application as absorbents, for separation and as phosphors.     

The role of SO2 in the reduction of NO by CO on La2O2S

The decomposition of NO and the reduction of NO by CO on La₂O₂S were studied using temperature-programmed reaction technique coupled with fast mass spectrometry, powder X-ray diffraction and X-ray photoelectron spectroscopy. The role of SO₂ plays in the reduction is explored. It is found that the decomposition of NO is a favorable reaction step for the reduction of NO by CO achieved through a sulfur-assisted path. The oxygen produced in the decomposition is removed by the sulfur in the oxysulfide as SO₂, which in turn is reduced back to sulfur by CO on La₂O₂S. An external supply of sulfur, such as SO₂, in the feed is needed to maintain the population of sulfur in the oxysulfide and thus make the reduction sustainable.     

Synthesis of FeBr3-cyclodextrin complexes in non-aqueous solution

Mixing FeBr₃ either solid or dissolved in ethyl ether, in acetonitrile or in dichloromethane with solid β-cyclodextrin, form different type of FeBr₃-cyclodextrin complexes as indicated by their stoichiometric composition and thermal and spectroscopic properties. The complexes are stable under usual atmospheric conditions. Water solutions of FeBr₃ at pH 12 containing cyclodextrin are stable over 24 h. The solid complexes were characterized by DSC and TGA analysis as well as by IR spectroscopy. It is shown that the complexes obtained from the reaction of solid cyclodextrin with FeBr₃ dissolved in ethyl ether, acetonitrile, or dichloromethane catalyze the oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide although in different yields. The best complex for this purpose is the one prepared in CH₂Cl₂ which afforded the sulfoxide in good yield.     

Dilatometric study of anisotropic sintering of alumina/zirconia laminates with controlled fracture behaviour

Al₂O₃ and ZrO₂ monoliths as well as layered Al₂O₃/ZrO₂ composites with a varying layer thickness ratio were prepared by electrophoretic deposition. The sintering shrinkage of these materials in the transversal (perpendicular to the layers, i.e. in the direction of deposition) as well as in the longitudinal (parallel with layers interfaces) direction were monitored using high-temperature dilatometry. The sintering of layered composites exhibited anisotropic behaviour. The detailed study revealed that sintering shrinkage in the longitudinal direction was governed by alumina (material with a higher sintering temperature), whilst in the transversal direction it was accelerated by the directional sintering of zirconia layers. For interpretation of such anisotropic sintering kinetics, the Master Shrinkage Curve model was developed and applied. Crack propagation through laminates with a different alumina/zirconia thickness ratio was described with the help of scanning electron microscopy and confocal laser microscopy.