Acid-Base. Surface Electron Donatin6 &.Catai.Ytlc Properties Of Some Binary Mixed Oxides Containing Rare Earth Elements

Catalysis research underpins the science of modern chemical processing and fuel technologies. Catalysis is commercially one of the most important technologies in national economies. Solid state heterogeneous catalyst materials such as metal oxides and metal particles on ceramic oxide substrates are most common. They are typically used with commodity gases and liquid reactants. Selective oxidation catalysts of hydrocarbon feedstocks is the dominant process of converting them to key industrial chemicals, polymers and energy sources.[1] In the absence of a unique successfiil theory of heterogeneous catalysis, attempts are being made to correlate catalytic activity with some specific properties of the solid surface. Such correlations help to narrow down the search for a good catalyst for a given reaction. The heterogeneous catalytic performance of material depends on many factors such as [2] Crystal and surface structure of the catalyst. Thermodynamic stability of the catalyst and the reactant. Acid- base properties of the solid surface. Surface defect properties of the catalyst.Electronic and semiconducting properties and the band structure. Co-existence of dilferent types of ions or structures. Adsorption sites and adsorbed species such as oxygen.Preparation method of catalyst , surface area and nature of heat treatment. Molecular structure of the reactants. Many systematic investigations have been performed to correlate catalytic performances with the above mentioned properties. Many of these investigations remain isolated and further research is needed to bridge the gap in the present knowledge of the field.

Surface properties and catalytic activity of vanadia supported on rare earth oxides

An investigation on the physical and chemical characterisation of rare earth oxide supported vanadia is attempted in the present study. La2O3, Sm2O3 and DY2O3 serve the purpose of supports. Supported catalysts were prepared and characterised using various physico chemical techniques. A detailed investigation of acid base properties is also carried out. The nature of interaction of vanadia with lanthanide oxide is discussed and the effect of vanadia loading on the activity of the systems towards reactions of industrial importance is explored.

Acid base characteristics of binary oxides of Zr with Ce and La

The surface acidity and basicity of binary oxides of Zr with Ce and La are determined using a series of Hammet indicators and Ho,,max values are reported. The generation of new acid sites habe been ascribed to the charge imbalance of M1-O-M2 bonds, where M1 and M2 are metal atoms. Both Bronsted and Lewis acid sites contribute to the acidity of the oxides

Studies on Catalysis by Vanadia Supported On Metal Oxides

Catalysis is an essential technology in manufacturing industries. The investigation based on supported vanadia catalysts and it’s sulfated analogues. Vanadia is a transition metal oxide and is used in oxidation reactions in chemical industry. It is more active and selective catalysts on suitable supports. The work deals with preparation of vanadia incorporated tin oxide and zirconia systems by wet impregnation. Physico-chemical characterization using instrumental techniques like BET etc. The surface acidic properties were determined by the ammonia TPD studies, Perylene absorption studies and Cumene conversion reaction. The catalytic activities of the prepared systems are tested by Friedel-Crafts benzylation of arenes and Bechmann rearrangement of Cyclohexanol oxime. Here the rector reactions are relatively rare. So to test the application of the catalyst systems for the selective oxidation of cyclohexanol to cyclohexanone and finally evaluate the catalytic activity of the systems for the vapour phase oxidative dehydrogenation of Ethylbenzene, which leads to the formation of Industrially important compound ‘styrene’ is another objective of this work

Preparation and characterisation of certain II-VI, I-III-VI2 semiconductor thin films and transparent conducting oxides

There is an increasing demand for renewable energies due to the limited availability of fossil and nuclear fuels and due to growing environmental problems. Photovoltaic (PV) energy conversion has the potential to contribute significantly to the electrical energy generation in the future. Currently, the cost for photovoltaic systems is one of the main obstacles preventing production and application on a large scale. The photovoltaic research is now focused on the development of materials that will allow mass production without compromising on the conversion efficiencies. Among important selection criteria of PV material and in particular for thin films, are a suitable band gap, high absorption coefficient and reproducible deposition processes capable of large-volume and low cost production. The chalcopyrite semiconductor thin films such as Copper indium selenide and Copper indium sulphide are the materials that are being intensively investigated for lowering the cost of solar cells. Conversion efficiencies of 19 % have been reported for laboratory scale solar cell based on CuInSe2 and its alloys. The main objective of this thesis work is to optimise the growth conditions of materials suitable for the fabrication of solar cell, employing cost effective techniques. A typical heterojunction thin film solar cell consists of an absorber layer, buffer layer and transparent conducting contacts. The most appropriate techniques have been used for depositing these different layers, viz; chemical bath deposition for the window layer, flash evaporation and two-stage process for the absorber layer, and RF magnetron sputtering for the transparent conducting layer. Low cost experimental setups were fabricated for selenisation and sulphurisation experiments, and the magnetron gun for the RF sputtering was indigenously fabricated. The films thus grown were characterised using different tools. A powder X-ray diffractometer was used to analyse the crystalline nature of the films. The energy dispersive X-ray analysis (EDX) and scanning electron microscopy i (SEM) were used for evaluating the composition and morphology of the films. Optical properties were investigated using the UV-Vis-NIR spectrophotometer by recording the transmission/absorption spectra. The electrical properties were studied using the two probe and four probe electrical measurements. Nature of conductivity of the films was determined by thermoprobe and thermopower measurements. The deposition conditions and the process parameters were optimised based on these characterisations.

Synthesis and Spectral Characterization of Lanthanide Complexes with Sulfamethoxazole and Their Antibacterial Activity

A series of nonelectrolytic lanthanide(III) complexes, [ ML 2 Cl 3 ] · 2 H 2 O, where M is lanthanum(III), praseodymium(III), neodymium(III), samarium(III), gadolinium(III), terbium(III), dysprosium(III), and yttrium(III), containing sulfamethoxazole ligand (L) are prepared. The structure and bonding of the ligand are studied by elemental analysis, magnetic susceptibility measurements, IR, 1 H NMR, TG / DTA , X-ray diffraction studies, and electronic spectra of the complexes. The stereochemistry around the metal ions is a monocapped trigonal prism in which four of the coordination sites are occupied by two each from two chelating ligands, sulfonyl oxygen, and nitrogen of the amide group and the remaining three positions are occupied by three chlorines. The ligand and the new complexes were tested in vitro to evaluate their activity against the bacteria Escherichia coli and Staphylococcus aureus.

Semiconductor Oxides Mediated Photocatalytic Removal of Chemical and Bacterial Pollutants from Wastewater

School of Environmental Studies, Cochin University of Science and Technology

Surface electron properties and catalytic activity of cerium-zirconium mixed oxides

The electron donating properties, surface acidity/ basicity and catalytic activity of cerium - zirconium mixed oxides at various compositions have been reported at an activation temperature of 500 degree C. The catalytic activity for the esterification of acetic acid with n-butanol has heen correlated with electron donating properties and surface acidity/basicity of the oxides.

Alkylation of phenol with methanol over mixed oxides of tin with some rare earth elements

Alkylation of phenol with methanol has been carried out over Sn-La and Sn-Sm mixed oxides of varying compositions at 623 K in a vapour phase flow reactor. It is found that the product selectivity is greatly influenced by the acid-base properties of the catalysts. Ortho-cresol formation is favoured over catalysts with weak acid sites whereas formation of 2,6-xylenol occurs in the presence of stronger acid sites. The cyclohexanol decomposition reaction and titrimetric method using Hammett indicators have been employed to elucidate the acid-base properties of the catalysts.

Catalysis by sulphated tin oxide modified with some transition metal oxides

In the present work, we have tried to evaluate systematically the surface properties of sulphated tin oxide systems modified with three different transition metal oxides viz. iron oxide, tungsten oxide and molybdenum oxide. The catalytic activities of these systems are checked and compared by carrying out some industrially important reactions such as oxidative dehydrogenation of ethylbenzene and Friedel-Crafts reactions.