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Doctoral Degrees (Chemistry)

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Browsing Doctoral Degrees (Chemistry) by Subject "Alkanes."

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    Oxidative dehydrogenation of n-octane using vanadium-based hydrotalcite-like compounds.
    (2010) Bux, Mayashree.; Friedrich, Holger Bernhard.
    The oxidative dehydrogenation of alkanes provides a potential route to higher value products such as olefins and aromatic compounds. Alkanes are of low environmental impact and their increasing availability has prompted extensive research in the field of alkane activation. The use of hydrotalcite-type compounds (HTlc), to achieve such reactions, has received much attention over recent years. Specifically, hydrotalcites and hydrotalcite-like compounds are promising catalysts because they provide a route to mixed-metal oxides with variable composition and significantly high metal-oxide distribution. Vanadium containing hydrotalcite-like catalysts were synthesized via the co-precipitation route and doped with either barium, cesium or boron using the wet impregnation method. These catalysts were characterized using electron microscopy, inductively coupled plasma - optical emission spectroscopy, X-Ray diffraction, differential thermal analysis, BET surface area measurements and infrared spectroscopy. The catalysts were then tested in a fixed bed reactor using n-octane as the feed and air as the oxidant. The effect of fuel-air ratios and contact time was studied on the unpromoted Mg-V-HTlc. The conversion of n-octane and the selectivity and yields to the products were quantified using gas chromatography and used to determine optimum reaction conditions. The effect of promoters on the conversion of n-octane and the selectivity of the catalyst in terms of products was determined under the optimum reaction conditions.  
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    The synthesis and reactions of functionalised transition metal substituted paraffins.
    (2002) Onani, Martin Opiyo.; Friedrich, Holger Bernhard.
    The compounds [Cp(CO)3W{(CH2)nX}] (X = Br, I; n = 3 - 6) were prepared in high yield by the reaction ofNa[Cp(CO)3W ] with Br(CH2)nBr. The bromoalkyl compounds were subsequently reacted with NaI to give the corresponding iodoalkyl complexes. The crystal structures of [Cp(CO)3W{(CH2)sI}] and [Cp(CO)3W{(CH2)3Br}] are reported for the first time. The former compound forms orthorhombic crystals in the space group P21nb and the latter forms triclinic crystals in the space group PI. Both have W-C bond lengths of2.35 A. The C-I bond length is 2.12 A; the C-Br bond length is 1.94 A. In a similar manner to the above, the compounds [Cp(CO)2(PPhiMe3 - i)Mo{(CH2)nBr}] (Cp = TJs-CsHs, n = 3, 4; i = 0 3) and [Cp*(CO)3Mo{(CH2)nBr}] (Cp* = TJs-CS(CH3)s,n = 3, 4) were prepared in medium to high yield by the reaction of the corresponding anion [Cp(CO)2(PPhjMe3-i)Mor or [Cp*(CO)3Mor with Br(CH2)nBr. The bromoalkyl compounds were subsequently reacted with NaI to give the corresponding iodoalkyl compounds [Cp(CO)2(PPhiMe3 _i)Mo{( CH2)nI}] (n = 3, 4; i = 0 - 3) and [Cp*(CO)3Mo{(CH2)nI}] (n = 3, 4) respectively. The iodoalkyl compounds were also prepared by the reaction of the corresponding anion and a,O)diiodoalkane in much lower yields. These compounds have been fully characterised and their properties are discussed. The crystal and molecular structure of [Cp(CO)2(PPh3)Mo{(CH2)3I}] is also reported, again for the first time. The compound forms crystals in the monoclinic space group P21/n; with a Mo-C bond length of 2.40 Aand a C-I bond length of 2.13 A These halogenoalkyl compounds were used as precursors to the new heterobimetallic complexes [Cp(CO)3W(CH2)nMo(CO)3Cp] n = 3 - 6; [Cp(CO)3W(CH2)nMo(COhCp*] n = 3,4; [Cp(CO)3W(CH2)nMo(CO)2(PPhiMe3_i)Cp] n = 3,4; i = 0 - 3 and [Cp(CO)2Fe(CH2)nMo(CO)2(PPhiMe3_i)Cp] n = 3,4; i = 0 - 3. The heterobimetallic complexes were prepared by the direct displacement of the iodide of a metallo-iodoalkyl complex with the appropriate anion. The complexes have been fully characterised by IR, IH NMR, 13C NMR, COSY, HETCOR or HSQC and elemental analyses. X-ray diffraction studies are for the first time reported for the complexes [Cp(CO)3W(CH2)3Mo(CO)2(PPh3)Cp] and [Cp(CO)2( PPh3)Mo(CH2)3Fe(CO)2Cp]. Both compounds form monoclinic crystals in the space group P 2I/c. The former, with a W-C bond length of2.32 Aand Mo-C bond length of2.35 Aand the latter with a Mo-C bond length of2.37 A and Fe-C bond length of2.08 A. The reactions of some of the above halogenoalkyl compounds with some simple inorganic molecules were investigated. The reactions of [Cp(CO)3W{CH2)4Br}] and [Cp(CO)2(PPhMe2)Mo{(CH2)3Br}] with silver nitrate in acetonitrile formed orange products, [Cp(CO)3W{(CH2)40N02}] and [Cp(CO)2(PPhMe2)Mo{(CH2)30N02}] respectively. The compounds [Cp(CO)3W{(CH2)sCN}], [Cp(CO)3W{(CH2)4CN}], [Cp(CO)2(PPhMe2)Mo{(CH2)3CN}], [Cp(CO)3W{(CH2)4N3}], [Cp(CO)3W{(CH2)sN3}], [Cp(CO)2(PPhMe2)Mo{(CH2)3N3}] were also obtained from various reactions using the reagents; AgCN, KCN, NaCN and NaN3. Similar reactions with molybdenum analogs gave cyclic carbene compounds. Reaction studies were also done on some of the above heterobimetallic compounds with tertiary phosphines; carbon monoxide gas and trityl salt, and thermolyses were also investigated. The reactions of PPh3 with [Cp(CO)3W{(CH2)3}MLy] {MLy = MO(CO)3Cp, MO(CO)3Cp* and MO(CO)2(PMe3)Cp} were found to be totally metalloselective, with the phosphines always attacking the expected metal site predicted by the reactions ofthe corresponding monometallic or homodinuclear alkyl species. A similar reaction involving CO with [Cp(CO)3W(CH2)3Mo(CO)3Cp] and [Cp(COhFe(CH2)3Mo(CO)2(PMe3)Cp] was also metalloselective. The reaction of [Cp(COhFe(CH2)4Mo(CO)3)Cp*] with trityl salt gave the expected complex [Cp(CO)2Fe(C4H7)Mo(CO)3)Cp*]PF6. It is believed that the structure of the trityl salt complex has the iron atom n-bonded whilst the molybdenum is cr-bonded to the butyl chain. The compounds [Cp(CO)3W(CH2)3Mo(CO)3Cp*] and [Cp(CO)2Fe(CH2)3Ru(CO)2Cp] both gave cyclopropane on thermolysis, indicating a ~elimination and reductive processes taking place. The crystal structure of [Cp(CO)3W{(CH2)3COOH}], which was obtained in one of the reaction studies, where the compound [Cp(CO)3W(CH2)3Mo(CO)2(PMe3)Cp] was reacted with excess PPh3in acetonitrile, is reported.