Catalysis of C-alkylation of phenol using V2O5-La2O3 system

Vapour phase methylation of phenol is carried out over La2O3 supported vanadia systems of various composition. The structural features and physico chemical characterisation of the catalysts are investigated. Orthovanadates are formed in addition to surface vanadyl species on the metal oxide support. No V2O5 crystallites are detected. The acid base properties of the oxides are studied by Hammett indicator method and decomposition of cyclohexanol.The data are correlated with the catalytic activity and selectivity of the products. Ring alkylation is found to be predominant over these catalysts.

Surface acidity and catalytic activity of mixed Fe-Al and Cr-Al pillared montmorillonites

The incorporation of transition metal oxide pillars such as those of iron and chromium along with Al2O3, pillars within the interlayers of a montmorillonite clay is investigated. The surface acidity of these catalysts has been evaluated for the first time employing the equilibrium adsorption of an electron donor, perylene, and the results are compared with those obtained by temperature programmed desorption of ammonia. The principle is based on the ability of a catalyst surface site to accept a single electron from an electron donor like perylene to form charge transfer complexes and the amount of adsorbed species is measured quantitatively by UV-vis spectroscopy. Fina1ly, an attempt has been made to correlate the acidity determined by the two independcnt methods and the catalytic activity of present systems in the benzoylation of toluene with benzoyl chloride. Incorporation of Fe and Cr has changed the properties of AI pitlared montmorillonite. Fe pillared systems have been found to be vcry good catalysts for benzoylation reaction

Studies on Catalysis by Titania

Scientists throughout the world are in search of a better methodology to reduce the use of environmentally hazardous chemicals common in industries .A significant contribution in this field is given by different redox catalysts in oxidation reactions. The oxidation of organic substrates represents one of the most important industrial chemical reactions, explaining the significant efforts invested in the research and development of new heterogeneous catalysts with increased activities and selectivities in these type reactions[l-4|. Hence liquid phase reactions like epoxidation of cylcohexene and hydroxylation of phenol were carried out with a new outlook in the challenge using CeO2/TiO;; and CuO/TiO2 catalysts denoted as TiO2-Ce as TiO2-Cu respectively in this work. Also different wt% of metals incorporated titania catalysts like 3, 6, 9 wt% CeO2/TiO; and CuO/TiO;were subjected to the present study .The interaction between metal oxides and the oxide supports have attracted much attention because of the wide applications of supported metal oxide systems[7,8]. It is well known that supported oxides of transition metals are widely used as catalysts for various reactions. Titania as well its metal modified catalysts systems afford high activity and selectivity in the liquid phase epoxidation of cyclohexene[9]. Cyclohexene epoxide is obtained as the major product during the reaction with small amounts of allylic substitution products.This chapter gives an idea about the liquid phase oxidation reactions like epoxidation of cylcohexene and hydroxylation of phenol in which many industrially important products are formed. Here discusses about the redox properties of the ceria and copper incorporated titania catalysts.The epoxidation of cyclohcxene is carried out efficiently over the prepared systems with the selective formation of cyclohexane epoxide. This reaction hints that it might be possible to create cleaner nylon chemistry. The total acidity of the prepared systems plays an important role in determining the catalytic activity in the dehydrogenation of cyclohexane and cyclohexene. The total acidity of the prepared systems plays an important role in determining the catalytic activity in the dehydrogenation of cyclohexane and cyclohexene.

Synthesis, Characterization and Applications of Hybrid Nanocomposites of TiO2 With Conducting Polymers

A nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), or structures having nano-scale repeat distances between the different phases that make up the material. In the broadest sense this definition can include porous media, colloids, gels and copolymers, but is more usually taken to mean the solid combination of a bulk matrix and nano-dimensional phase(s) differing in properties due to dissimilarities in structure and chemistry. The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nanocomposite will differ markedly from that of the component materials. Size limits for these effects have been proposed, <5 nm for catalytic activity, <20 nm for making a hard magnetic material soft, <50 nm for refractive index changes, and <100 nm for achieving superparamagnetism, mechanical strengthening or restricting matrix dislocation movement. Conducting polymers have attracted much attention due to high electrical conductivity, ease of preparation, good environmental stability and wide variety of applications in light-emitting, biosensor chemical sensor, separation membrane and electronic devices. The most widely studied conducting polymers are polypyrrole, polyaniline, polythiophene etc. Conducting polymers provide tremendous scope for tuning of their electrical conductivity from semiconducting to metallic region by way of doping and are organic electro chromic materials with chemically active surface. But they are chemically very sensitive and have poor mechanical properties and thus possessing a processibility problem. Nanomaterial shows the presence of more sites for surface reactivity, they possess good mechanical properties and good dispersant too. Thus nanocomposites formed by combining conducting polymers and inorganic oxide nanoparticles possess the good properties of both the constituents and thus enhanced their utility. The properties of such type of nanocomposite are strongly depending on concentration of nanomaterials to be added. Conducting polymer composites is some suitable composition of a conducting polymer with one or more inorganic nanoparticles so that their desirable properties are combined successfully. The composites of core shell metal oxide particles-conducting polymer combine the electrical properties of the polymer shell and the magnetic, optical, electrical or catalytic characteristics of the metal oxide core, which could greatly widen their applicability in the fields of catalysis, electronics and optics. Moreover nanocomposite material composed of conducting polymers & oxides have open more field of application such as drug delivery, conductive paints, rechargeable batteries, toners in photocopying, smart windows, etc.The present work is mainly focussed on the synthesis, characterization and various application studies of conducting polymer modified TiO2 nanocomposites. The conclusions of the present work are outlined below, Mesoporous TiO2 was prepared by the cationic surfactant P123 assisted hydrothermal synthesis route and conducting polymer modified TiO2 nanocomposites were also prepared via the same technique. All the prepared systems show XRD pattern corresponding to anatase phase of TiO2, which means that there is no phase change occurring even after conducting polymer modification. Raman spectroscopy gives supporting evidence for the XRD results. It also confirms the incorporation of the polymer. The mesoporous nature and surface area of the prepared samples were analysed by N2 adsorption desorption studies and the mesoporous ordering can be confirmed by low angle XRD measurementThe morphology of the prepared samples was obtained from both SEM & TEM. The elemental analysis of the samples was performed by EDX analysisThe hybrid composite formation is confirmed by FT-IR spectroscopy and X-ray photoelectron spectroscopyAll the prepared samples have been used for the photocatalytic degradation of dyes, antibiotic, endocrine disruptors and some other organic pollutants. Photocatalytic antibacterial activity studies were also performed using the prepared systemsAll the prepared samples have been used for the photocatalytic degradation of dyes, antibiotic, endocrine disruptors and some other organic pollutants. Photocatalytic antibacterial activity studies were also performed using the prepared systems Polyaniline modified TiO2 nanocomposite systems were found to have good antibacterial activity. Thermal diffusivity studies of the polyaniline modified systems were carried out using thermal lens technique. It is observed that as the amount of polyaniline in the composite increases the thermal diffusivity also increases. The prepared systems can be used as an excellent coolant in various industrial purposes. Nonlinear optical properties (3rd order nonlinearity) of the polyaniline modified systems were studied using Z scan technique. The prepared materials can be used for optical limiting Applications. Lasing studies of polyaniline modified TiO2 systems were carried out and the studies reveal that TiO2 - Polyaniline composite is a potential dye laser gain medium.

Catalyst

A water gas shift catalyst comprising metal particles and a metal oxide material is disclosed. The metal particles comprise at least one precious metal and the metal oxide material comprises at least one reducible metal oxide. Substantially all of the metal particles are encapsulated by the metal oxide material such that the catalyst has substantially no activity for methanation. The loading of the metal particles is between 0.5-25wt% based on the weight of the metal oxide material. A process for preparing the catalyst is also disclosed.

Theoretical investigation of Hf and Zr defects in c-Ge

The introduction of high-permittivity gate dielectric materials into complementary metal oxide semiconductor technology has reopened the interest in Ge as a channel material mainly due to its high hole mobility. Since HfO(2) and ZrO(2) are two of the most promising dielectric candidates, it is important to investigate if Hf and Zr may diffuse into the Ge channel. Therefore, using ab initio density functional theory calculations, we have studied substitutional and interstitial Hf and Zr impurities in c-Ge, looking for neutral defects. We find that (i) substitutional Zr and Hf defects are energetically more favorable than interstitial defects; (ii) under oxygen-rich conditions, neither Zr nor Hf migration towards the channel is likely to occur; (iii) either under Hf- or Zr-rich conditions it is very likely, particularly for Zr, that defects will be incorporated in the channel.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Inverse opal structure of SnO2 and SnO2 : Zn for gas sensing

In the present work, we propose a low cost synthetic sol-gel route that allows to produce high quality oxide nanostructures with inverse opal architecture which, transferred on alumina substrates provided with Pt interdigitated contacts and heater, are tested as gas sensing devices. An opal template of sintered monodisperse polystyrene spheres was filled with alcoholic solutions of metal oxide precursors and transferred on the alumina substrate. The polystyrene template was removed by thermal treatment, leading to the simultaneous sintering of the oxide nanoparticles. Beside SnO₂, a binary oxide well known for gas sensing application, a Zn containing ternary solid solution (SnO₂:Zn, with Zn 10% molar content) was taken into account for sensor preparation. The obtained high quality macro and meso-porous structures, characterized by different techniques, were tested for pollutant (CO, NO₂) and interfering (methanol) gases, showing that very good detection can be reached through the increase of surface area offered by the inverse opal structure and the tailoring of the chemical composition. The electrical characterization performed on the tin dioxide based sensors shows an enhancement of the relative response towards NO₂ at low temperatures in comparison with conventional SnO₂ sensors obtained with sputtering technique. The addition of Zn increases the separation between the operating temperatures for reducing and oxidizing gases and results in a further enhancement of the selectivity to NO₂ detection.

Inverse opal nanoassemblies : novel architectures for gas sensors the SnO2:Zn case

A novel technique is here presented, based on inverse opal metal oxide structures for the production of high quality macro and meso-porous structures for gas sensing. Taking advantage of a sol-gel templated approach. different mixed semiconducting oxides with high surface area, commonly used in chemical sensing application, were synthesized. In this work we report the
comparison between SnO₂ and SnO₂:Zn. As witnessed by Scanning and Transmission Electron Microscopy (SEM and TEM) analyses and by Powder x-ray Diffraction (PX RD), highly ordered meso-porous structures were formed with oxide crystalline size never exceeding 20 nm . The filled templates. in form of thick films, were bound to allumina substrate with Pt interdigitated contacts
and Pt heater, through in situ calcination, in order to perform standard electrical characterization. Pollutant gases like CO and NO₂ and methanol. as interfering gas, were used for the targeted electrical gas tests. All samples showed low detection limits towards both reducing and oxidizing species in low temperature measurements. Moreover, the addition of high molar percentages of Zn( II) affected the beha viour of electrical response improv ing the se lecti vity of the proposed system.

Process for the production of ultrafine powders

A process for the production of ultrafine powders consisting of individual particles with sizes in the range of 1 nm to 200 nm, which is based on the mechanical milling of two or more non-reacting powders. The process includes subjecting a suitable precursor metal compound and a non-reactant diluent phased to mechanical milling which through the process of mechanical activation reduces the microstructure of the mixture of the form of nano-sized grains of the metal compound uniformly dispersed in the diluent phase. Heat treating the milled powder converts the nano-sized grains of the precursor metal compound into a desired metal oxide phase. Alternatively, the precursor metal compound may itself be an oxide phase which has the requisite milling properties to form nanograins when milled with a diluent. An ultrafine powder is produced by removing the diluent phase such that nano-sized grains of the desired metal oxide phase are left behind. The process facilitates a significant degree of control over the particle size and size distribution of the particles in the ultrafine powder by controlling the parameters of mechanical activation and heat treatment.

Development and application of electroanalytical field-based chemical monitoring systems

The development and application of a novel combination of electrochemical techniques and computerized field-based battery-operated instrumentation is investigated. Low-power complementary metal oxide semiconductor technology has been utilized for the development of the field data acquisition systems and the instrumental performance of the complete analytical system is critically evaluated.

Ultrasensitive hydrogen sensor based on Pd0-loaded SnO2 electrospun nanofibers at room temperature

Pd0-loaded SnO2 nanofibers have been successfully synthesized with different loaded levels via electrospinning process, sintering technology, and in situ reduction. This simple strategy could be expected to extend for the fabrication of similar metal?oxide loaded nanofibers using different precursors. The morphological and structural characteristics of the resultant product were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). To demonstrate the usage of such Pd0-loaded SnO2 nanomaterial, a chemical gas sensor has been fabricated and investigated for H2 detection. The sensing performances versus Pd0-loaded levels have been investigated in detail. An ultralow limit of detection (20 ppb), high response, fast response and recovery, and selectivity have been obtained on the basis of the sensors operating at room temperature. The combination of SnO2 crystal structure and catalytic activity of Pd0-loaded gives a very attractive sensing behavior for applications as real-time monitoring gas sensors.

Synthesis and growth mechanism of Thin-film TiO2 nanotube arrays on focused-ion-beam micropatterned 3D isolated regions of titanium on silicon

In this paper, the fabrication and growth mechanism of net-shaped micropatterned self-organized thin-film TiO2 nanotube (TFTN) arrays on a silicon substrate are reported. Electrochemical anodization is used to grow the nanotubes from thin-film titanium sputtered on a silicon substrate with an average diameter of ?30 nm and a length of ?1.5 ?m using aqueous and organic-based types of electrolytes. The fabrication and growth mechanism of TFTN arrays from micropatterned three-dimensional isolated islands of sputtered titanium on a silicon substrate is demonstrated for the first time using focused-ion-beam (FIB) technique. This work demonstrates the use of the FIB technique as a simple, high-resolution, and maskless method for high-aspect-ratio etching for the creation of isolated islands and shows great promise toward the use of the proposed approach for the development of metal oxide nanostructured devices and their integration with micro- and nanosystems within silicon-based integrated-circuit devices.

The corrosion inhibition of aluminium alloy 7075-T651 with cerium and Mischmetal di phenyl phosphate

Previous studies have shown that cerium diphenyl phosphate (Cedpp) 3 is a very effective inhibitor of corrosion of aluminium alloys in chloride solutions. This paper describes the results of further studies using electrochemical and constant immersion corrosion tests to compare the effectiveness of Ce(dpp) 3 and Mischmetal diphenyl phosphate Mm(dpp) 3 as inhibitors of corrosion pitting on AA7075-T651 aluminium alloy. The results shows that both Ce(dpp) 3 and Mm(dpp) 3 are excellent inhibitors of pitting corrosion of this alloy in very aggressive environments of continuously aerated 0.1M and 1.0M sodium chloride (NaCl) solutions. Polarisation tests indicate that these compounds act as a cathodic inhibitors by reducing the rate of the oxygen reduction reaction, which results in a decreased corrosion current density and a separation of the corrosion potential from the pitting potential. This inhibition is thought to be due to the formation of a surface film consisting of rare earth metal oxide, aluminium oxide and a cerium-aluminium organo-phosphate complex. Surface analysis data from scanning electron microscopy and X-ray Energy Dispersive Spectroscopy show the complex nature of this protective film. This work further develops our understanding about the mechanisms through which these complex films form, and how inhibition occurs in the presence of these compounds.

Binding affinities of amino acid analogues at the charged aqueous titania interface : implications for titania-binding peptides

Despite the extensive utilization of biomolecule-titania interfaces, biomolecular recognition and interactions at the aqueous titania interface remain far from being fully understood. Here, atomistic molecular dynamics simulations, in partnership with metadynamics, are used to calculate the free energy of adsorption of different amino acid side chain analogues at the negatively-charged aqueous rutile TiO2 (110) interface, under conditions corresponding with neutral pH. Our calculations predict that charged amino acid analogues have a relatively high affinity to the titania surface, with the arginine analogue predicted to be the strongest binder. Interactions between uncharged amino acid analogues and titania are found to be repulsive or weak at best. All of the residues that bound to the negatively-charged interface show a relatively stronger adsorption compared with the charge-neutral interface, including the negatively-charged analogue. Of the analogues that are found to bind to the titania surface, the rank ordering of the binding affinities is predicted to be "arginine" > "lysine" ≈ aspartic acid > "serine". This is the same ordering as was found previously for the charge-neutral aqueous titania interface. Our results show very good agreement with available experimental data and can provide a baseline for the interpretation of peptide-TiO2 adsorption data.