Oxidation of CO in microchannels of ceramic membranes modified with oxide catalytic coatings

Ceramic and cermet membranes containing catalytic coatings in the internal volume of their channels were obtained. A relationship between the permeability and kinetic regularities of CO oxidation describing the transmembrane flow of gases was studied. The pre-exponential factor and apparent activation energy change as the loading of the membrane channels by the catalyst proceeds. The study of gas permeability through the membranes showed that the catalyst with a loose branched surface is distributed in the membrane microchannels. The reaction rate constant increases in parallel with an increase in the relative fraction of the catalyst surface. The CO oxidation rate is assumed to depend statistically on the number of active sites, which increases with filling of the membrane channels by the catalytic material.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2613–2619, December, 2004.     

Asymmetric membranes with modified gold films as selective gates for metal ion separations

Thin layers of gold (700 Å) were deposited on manufactured alumina pourous supports to yield nanopores with openings of <7 nm. A self-assembled monolayer (SAM) of alkyl thiols was then attached to provide a hydrophobic support for trialkyl phosphine oxide-based metal ion carriers. The resulting gated membranes provided a barrier to ions including H⁺, and Ca²⁺, NO₃⁻, and CH₃COO⁻. When an aqueous feed solution of 4.2 mM uranyl nitrate and 1 M lithium nitrate pH 4, and a receiving solution of 1 M sodium acetate pH 5.5 were used 100% of the metal was transported across the membrane by facilitated transport via the phosphate or phosphine oxide carrier. The thin gates transported metal ions as neutral nitrate complexes with fluxes high enough to be limited by the alumina support. The flux rates of 200,000 metal ions per pore per second are only a factor of 5 below that observed for the potassium channel. High selectivity of U over Eu is observed until the [U] is <0.84 mM in the feed solution, despite the fact the Eu actually transports faster when U is not present. This work demonstrates that selectivity can be added without impeding transport by using thin selective layers.     

Anodic aluminium oxide catalytic membranes for asymmetric epoxidation

Catechol-functionalized (salen)Mn complexes can be supported on mesoporous anodized aluminium oxide disks to yield catalytic membranes that are highly active in the enantioselective epoxidation of olefins when being deployed in a forced-through-flow reactor.     

改性氧化石墨烯膜的制备及其性能研究

为了改善氧化石墨烯(GO)膜的低渗透性和不稳定性,本文采用过氧化氢对GO进行改性后抽滤成膜,并在不同温度下对膜进行热还原.采用超高性能全自动气体吸附仪、透射电镜、扫描电镜、拉曼光谱仪、接触角、X射线衍射等对材料进行结构和形貌表征.分析不同HGO(H2O2改性GO)负载量和不同温度热还原对膜水通量和截留率的影响.在优化条...     

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Poly(phenylene oxide) films modified with allylamine plasma as a support for invertase immobilization

The paper describes a method for preparation of polymer support suitable for covalent invertase immobilization. Modification of poly(phenylene oxide) films by plasma polymerization of allylamine has been applied to introduce amine functionality on the polymer surface. It has been observed that the polymer surface became covered in plasma by a loosely fixed, moderately hydrophilic layer that should be removed before the immobilization process. The chemical character of the stable sub-layer has been related to several modification parameters: geometry of reactor, mode of plasma action and composition of gaseous mixture. Methods for determination of surface concentration of amine groups have also been presented and discussed from the immobilization point of view.     

Zeolite containing catalytic membranes as interphase contactors

In this study, a catalytic membrane reactor was developed. A titanium silicalite (TS-1) containing polydimethylsiloxane (PDMS) catalytic composite membrane was placed at the interface between the two immiscible phases containing respectively n-hexane (organic phase) and a solution of hydrogen peroxide (aqueous phase). This allowed adequate transport of both reactants to the catalyst surface, without using a co-solvent. This concept of zeolite containing catalytic membrane as interphase contactor, which may be applicable to numerous multiphase reactions, has been tested for the oxyfunctionalization of n-hexane to a mixture of hexanols and hexanones using H₂O₂ as the oxidant. It was shown that the oxyfunctionalization products are formed in and separated by the catalytic membrane. The experimental results illustrated the technical advantages of such a catalytic membrane reactor since the observed conversion and selectivity are similar to the ones obtained with the same catalyst in a conventional reactor. The various factors (membrane thickness, catalyst loading and membrane modifications) which may affect the membrane catalytic and permeation performances were investigated.     

Fabrication of nanoreactors based on polyoxoperoxometalates and enhancement of their catalytic activity

The nanoreactors were fabricated by reacting amphiphilic quaternary ammoniums and polyoxoperoxometalates K_n[PW_12-xTi_x- O_40-x（O₂）_x]（x=1,2 and 3;n = 5,7 and 9）(K₅[PW₁₁TiO₃₉（O₂）],K₇[PW₁₀Ti₂O₃₈（O₂）₂]and K₉[PW₉Ti₃O₃₇（O₂）₃]).Fourier transform infrared spectroscopy（FT-IR）,transmission electron microscopy（TEM） were used to characterize the resulting samples. This kind of nanocatalysts could promote NH₄SCN’ degradation into simple inorganic compounds such as SO₄^2-,HCO₃^- and NO₃^- only using oxygen as an oxidant under room conditions.     

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH₃-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.     

Role of the surface hydroxyl groups of modified titanium oxide in catalytic ethylene oxide hydration

A quantum-chemical study of the mechanism of ethylene oxide hydration on titanium oxide (anatase) modified with phosphorus additives was performed. It was demonstrated that the hydroxyl groups of the anatase surface are of importance for the activation interaction of ethylene oxide with the catalyst surface. The activation of the ethylene oxide molecule and proton transfer occur with the participation of these hydroxyl groups. It was found that the modification of the titanium oxide surface with phosphorus additives plays a crucial role in proton transfer.     

Direct Henry reactions with modified calcium oxide as solid catalyst

Commercial CaO was modified simply with benzyl bromide. The modified CaO had good water resistance, and characterization by FTIR and TG revealed the modifier was chemically bonded to the CaO surface. Commercial CaO and CaO modified with benzyl bromide were investigated as catalysts for the Henry reaction between benzaldehyde and nitromethane. It was found that the catalytic activity of the modified CaO was greatly improved, with high conversion of benzaldehyde to the (E)-phenyl nitroolefin and 1-phenyl-2-nitroethanol, and with different selectivity from commercial CaO. The effect of modification and reaction conditions on yield, selectivity, and mechanism were studied thoroughly.     

Composite films based on polyphenylene oxide modified with endofullerenes C60 with encapsulated iron atoms

Russian Journal of Applied Chemistry - New diffusion membranes were prepared by introducing endofullerenes with encapsulated iron atoms, Fe@C60, into the poly-2,6-dimethyl-1,4-phenylene oxide...     

Kinetically controlled catalytic formation of zinc oxide thin films at low temperature

We developed a unique method to produce ZnO thin films by kinetically controlled catalytic hydrolysis of a molecular precursor at low temperature, operating in conjunction with the vectorial control of crystal growth. Using a system in which the diffusion of a volatile catalyst into a solution of molecular precursor of the metal oxide limits the rate of hydrolysis and establishes a gradient of catalyst concentration, we investigated the nucleation of textured nanoparticles at the gas-liquid interface and characterized their subsequent growth. Use of this slow diffusion method combined with prediction of molecular species using a partial charge model enables a higher level of organizational control than obtained in other low-temperature synthesis methods, without the use of organic molecules. Various metal oxides and their morphologies and chemical compositions can be tailored for specific applications using this relatively simple approach.     

Chemically modified opals as thin permselective nanoporous membranes

Thin-film opals comprising three layers of 440 nm diameter SiO2 spheres were assembled on Pt electrodes and modified with amino groups on the silica surface. Diffusion of anionic, cationic, and neutral redox species through the opals was studied by cyclic voltammetry. The chemically modified opal membranes demonstrate high molecular throughput and, at low pH, selectively block transport of a cationic redox species relative to that of anionic and neutral redox species. This permselective behavior is attributed to the electrostatic interactions that are enhanced by the tortuous pathway within the opal and by the high surface area of the chemically modified spheres.     

Chitosan‐modified graphene oxide as a modifier for improving the structure and performance of forward osmosis membranes

Chitosan (CS) with good hydrophilicity and charged property was used to modify graphene oxide (GO), the obtained GO‐CS was used as a novel modifier to fabricate thin film composite forward osmosis (FO) membranes. The results revealed that the amino groups on CS reacted with carboxyl groups on GO, and the lamellar structure of the GO nanosheets was peeled off by CS, resulting in the reducing of their thicknesses. The GO‐CS improved the hydrophilicity of polyethersulfone (PES) substrate, and their contact angles decreased to 64° with the addition of GO‐CS in the substrate. GO‐CS also increased the porosity of the substrate and surface roughness of FO membrane, thereby optimizing the water flux and reverse salt flux of FO membrane. The average water flux of the FO membrane reached the optimal flux of 21.34 L/(m² h) when GO‐CS addition was 0.5 wt%, and further addition of GO‐CS to the substrate would decrease the water flux of FO membrane, and the reverse salt flux also decreased to the lowest value of 2.26 g/(m² h). However, the salt rejection of the membrane increased from 91.4% to 95.1% when GO‐CS addition increased from 0.5 to 1.0 wt% under FO mode using 1 mol/L sodium chloride (NaCl) solution as draw solution (DS). In addition, high osmotic pressure favored water permeation, and at the same concentration of DS, magnesium chloride (MgCl₂) exhibited better properties than NaCl. These results all suggested that GO‐CS was a good modifier to fabricate FO membrane, and MgCl₂ was a good DS candidate.     

Application of hydroxy sodalite films as novel water selective membranes

Supported hydroxy sodalite (H-SOD) membranes were prepared on α-alumina disks using direct hydrothermal synthesis at 413 K for 3.5 h. The continuity of the membranes was verified using single gas permeation of He and N₂ at ambient conditions. The membranes were impermeable to N₂ and He, which validated absence of defects in the membrane structure. The membranes were used in dewatering several organic alcohol/water mixtures (organic alcohol being: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, and 2-pentanol). The influence of feed temperature (303–473 K), feed concentration (0–100 mol% alcohol in the feed), and absolute feed pressure (1.6–2.4 MPa) on the water flux were analyzed. The absolute feed pressure had no effect on the water permeance. The membrane exhibited a water/alcohol separation factor larger than 10⁶ and showed excellent thermal, mechanical, and operation stability in continuously dehydrating a water/ethanol mixture (72 mol% water) by pervaporation at 473 K and 2.2 MPa for 125 h. The normalized water flux correlated well with the water feed concentration for the primary alcohols. Below 40 mol% water in mixtures with secondary alcohols the water flux was three orders of magnitude lower. The water mobility through the membrane had an activation energy of ∼15 kJ/mol.     

Structural,chemical, and dynamic characteristics of ceramic membranes modified with self-organized supramolecular silicon oxide systems

The changes in structural characteristics, chemical composition, and gas permeability of the modified ceramic asymmetric tubular membranes were studied. The membranes were tested in permeability and selectivity of two gaseous mixtures (H/He and H/Ar). The structure of the modified coating was examined by X-ray powder diffraction and by transmission and scanning electron microscopies.     

Metalloporphyrin chemically modified glassy carbon electrodes as catalytic voltammetric sensors

Metalloporphyrin-coated glassy carbon electrodes are used as electrocatalytic voltammetric sensors for numerous clinically important solutes. For such compounds, heterogeneous charge- transfer rates are often very slow at carbon electrodes, leading to poorly defined voltammetric responses. The metalloporphyrin-modified electrodes are shown to decrease by several hundred millivolts the potential required for the oxidation of ascorbic acid, penicillamine, acetaminophen, dihydronicotinamide adenine dinucleotide, hydralazine, epinephrine, cysteine and oxalic acid. The faster rates of electron transfer result in a well defined voltammetric response and increased sensitivity. The differential pulse peaks for caffeic acid, ascorbic acid, acetaminophen and dopamine are enhanced by 18, 10.5, 9.4 and 8.4, respectively. When used for amperometric monitoring of flowing streams, the coated electrode permitted detection at lower potentials than at the naked surface and greatly facilitated assays of urine samples.     

Modification of electrodes with catalytic, size-exclusion films

The application of electroanalytical methodology to the study of liquid-phase samples can be complicated by the adsorption of sample components on the electrode surface. Macromolecules are particularly problematic in this regard. An early means of addressing this problem was to use a membrane permeable to the analyte as a barrier between the sample phase and the electrochemical cell. Amperometric determination of oxygen in biological fluids is a historically important example. This approach was refined by modifying electrodes with semi-permeable, conducting films applied directly to the surface of the working electrode. Cellulose acetate is an example of a conductive material that blocked adsorption of compounds in biological samples but was permeable to analytes such as hydrogen peroxide. Modification of electrodes with ion-exchange films and, more recently, porous sol?Cgel films was an expansion of this methodology. A complicating factor was that oxidation or reduction of most analytes requires a catalyst. The development of films that are size-exclusion barriers to interferents and incorporate an electron-transfer catalyst is described.     

Supported ionic-liquid films (SILF) as two-dimensional nanoreactors for enantioselective reactions: surface-mediated selectivity modulation (SMSM)

Supported ionic-liquid films (SILF) of nanometric thickness containing bis(oxazoline)-copper complexes can be used as recoverable catalysts for enantioselective cyclopropanation reactions. When a thin film of ionic liquid is supported on a clay, the system behaves as a nearly two-dimensional nanoreactor in which the restrictions in rotational mobility and the close proximity to the surface support produce variations in the stereo- and enantioselectivities, leading to a complete reversal of the overall selectivity of the reaction. As an example, the cyclopropanation of styrene changes from a preference for the (1S,2S)-trans isomer in bulk solution to the (1R,2S)-cis isomer in the SILF. This variation is strongly dependent on both the thickness of the film and the nature of the support. Only layered solids with negative charges in the layers (clays) give rise to this type of behaviour, showing that the formation of ion pairs may be a decisive factor. This unexpected effect also shows the existence of differences between bulk and supported ionic liquids.