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Application of supported palladium towards the electrocatalytic oxidation of low molecular weight alcohol (methanol)

  • Authors: Siwal, Samarjeet Singh
  • Date: 2017
  • Subjects: Palladium catalysts , Oxidation , Fuel cells - Materials , Electrocatalysis - Research
  • Language: English
  • Type: Doctoral (Thesis)
  • Identifier: http://hdl.handle.net/10210/493418 , uj:45099
  • Description: Abstract: In present scenario, direct methanol fuel cell (DMFC) becoming more familiar and promising fuel cell due to its straightforward configuration system & weight and elevated power generation efficiency. This thesis focuses on metal nanoparticles based nanocomposite which is prepared by using in situ polymerization and composite formation (IPCF) technique and used for fuel cell application. The MNP-CP composite system was deposited on WE by drop and dry method. The integration of various nanomaterials is described, in order to understand the effect of different surface modifications and morphologies of various materials for electrooxidation of low molecular weight alcohols (C1-C4). In this work, IPCF approaches are the promising methods to fabricate the key building blocks of nanocomposites system for fundamental research. The entire work of the thesis contributes in the field of fuel cell by exploring the applicability’s of conductive polymer (CP) and metallic nanoparticles (MNPs) based nanocomposite systems. In general, potentiometric and amperometric electrochemical approach were employed to model the electrochemical performance of the CP-MNP. The CP-MNP composite were used to modify the working electrode (WE) i.e. glassy carbon electrodes (GCE). The intimate contact between CP and MNP in nanocomposites system were characterize by optical microscopic techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultra-violet visible (UV) spectrophotometer, X-ray diffraction (XRD) pattern, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL)... , Ph.D. (Chemistry)
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Die gebruik van dimetieldioksiraan vir die selektiewe oksidasie van koolwaterstowwe

  • Authors: Dixon, John Thomas
  • Date: 2014-02-11
  • Subjects: Hydrocarbons , Oxidation
  • Type: Thesis
  • Identifier: uj:3880 , http://hdl.handle.net/10210/9247
  • Description: M.Sc. (Chemistry) , This study was directed towards the investigation of oxidations by dimethyldioxirane, a new and versatile oxidant. To begin, the oxidation of various simple saturated hydrocarbons was examined. These oxidations gave alcohols in yields that varied considerably. This investigation showed that dimethyldioxirane reacts chemoselectively and that a preference is shown for tertiary C-H bonds and even more so for tertiary cis C-H bonds in bicyclic six-membered ring compounds and tertiary benzylic C-H bonds. A kinetic study of the oxidations of benzylic C-H bonds of various cumene derivatives by dimethyldioxirane confirmed the electrophilic nature of this reagent. In order to investigate the chemoselectivity of oxidations by dimethyldioxirane, the oxidation of eight steroids was examined. These oxidations were very selective and rarely gave more than two products. In all but one case, the oxidations selectively produced alcohols in good yields. The preference of dimethyldioxirane for tertiary cis C-H bonds in cyclic compounds and tertiary benzylic C-H bonds was confirmed by the oxidation' of an estrone derivative and two 5,8-5teroids. In all three cases the anticipated compounds were obtained as the major products. This oxidative method for the synthesis of 5,B-hydroxy steroids may provide a novel route for the synthesis of cardioactive steroids. The oxidation of a furo[2,3-b]benzofurane derivative was investigated to conclude this study of oxidations by dimethyldioxirane. The succesful oxidation of this compound at C-3a would furnish a synthon for aflatoxin M1 in a single step. Unfortunately, no product was obtained for the oxidation of the furo[2,3-b]benzofurane derivative by dimethyldioxirane. Futher studies into the source of this lack of reactivity are currently being undertaken.
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High temperature oxidation resistance of Ni22Cr11Al bond coat produced by spark plasma sintering as thermal barrier coatings

Oksidasie van suikers en aromatiese verbindings met dimetieldioksiraan

  • Authors: Siemens, Hester
  • Date: 2014-04-15
  • Subjects: Aromatic compounds , Sugars , Oxidation , Quinone
  • Type: Thesis
  • Identifier: uj:10679 , http://hdl.handle.net/10210/10195
  • Description: M.Sc. (Chemistry) , The aim of this study was to investigate the oxidation of aromatic compounds and benzylidene acetals with dimethyldioxinne. Dimethyldioxirane, either by Insitu preparation or in the isolated form, has shown remarkable reactivity. This oxidant is effective in oxygen transfer, readily prepared from commercial materials and reacts under mild conditions. Quinones are natural materials with biological activity and some are key intermediates in the synthesis of medicines. A well-known method for the preparation of quinones, is the oxidation of phenols and aromatic ethers. The oxidation of simple phenol and anisole derivatives by dimethyldioxirane yielded complex mixtures. More hindered aromatic compounds were investigated, since the oxidation of these compounds proceeded in a more controlled manner. In this study the phenols were found to be more reactive than the corresponding aromatic ethers. para-Quinones were formed preferentially, whereas ortho-quinones were observed in one or two cases. Products formed in these oxidations depend on the substitution pattern of the substrate. The oxidation of phenols and aromatic compounds formed complex mixtures and does not have many synthetic applications. Mechanisms are proposed for the formation of the different products. Benzylidene acetals are important protecting groups in the chemistry of carbohydrates. Cleavage of these benzylidene acetals gave either the free diol or benzyl ether or benzoyl ester, depending on the reagent used. The reaction of dimethyldioxirane with benzylidene acetals gave the benzoylesters. With dioxanes, e.g. 4,6-O-benzylidene sugar derivatives, there are no difference in stereoelectronic effects in the cleavage of C-4 and C-6. The major product has a 6-benzoate group, probably due to the greater stability of the primary benzoate. In dioxolanes both reactivity and regioselectivity of the reactions are influenced by stereoeleetronic effects. It has been found that the cleavage of dioxolanes took place preferably in a conformation where the oxygen is antiperiplanar towards the leaving group. It has been shown that dimethyldioxinme can be used with success in the deprotection of benzylidene acetals in the chemistry of carbohydrates.
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