The work described is mainly concerned with exploring the proposition that the cations of catalytically active metals, typically Ni<SUP>2+</SUP>, can be introduced not only between the layers of sheet silicates but within the sheets themselves as has previously been demonstrated to occur with Li<SUP>+</SUP> and H<SUP>+</SUP>. It is further proposed that following oxidation and reduction the inter-lamellar space will contain both those cations and the metal or its oxide, thus providing a bi-functional clay catalyst. The characterization of the various clay structures investigated has been carried out using atomic absorption spectrometer, cation exchange capacity determination, thermal gravimetric analysis, and Fourier transmission infra-red ray and X-ray diffraction spectroscopy. Identification of the products of catalytic reaction was carried out by the use of gas chromatography and coupled gas chromatography-mass spectrometry. It is shown that the basic propositions are confirmed and that a new modified clay catalyst called reduced-Ni-bentonite provides both metal-catalyzed and proton-catalyzed functions. Utilising this catalyst, alkenes such as 1.5 hexadiene and isoprene are hydrogenated, hydrogenated-dehydrogenated, and isomerized with considerable facility. It has been found that, under certain conditions, cyclic ether formation by water addition to the dialkene also occurs. The catalyst provides hexene isomers from hexadiene or from hex-1-ene, and the equilibrium distribution at 150<SUP>o</SUP>C, 200<SUP>o</SUP>C and 250<SUP>o</SUP>C has been determined. The work reveals that the hydrogenation reactions involve both the internal surface located metallic Ni and the interlamellar protons and Ni<SUP>2+</SUP> cations, whereas only interlamellar protons play a role in either the cyclic ether formation or hexene isomerizations. A study of the formation of the cyclic ether, 2.5 dimethyl tetrahydrofuran from 1.5 hexadiene and water using conventional H<SUP>+</SUP>-exchanged clay has shown that the addition of alcohol provides a method for continuous replacement of water at the interlamellar sites. This has commercial significance in the context of alkene-ether transformations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637955 |
| Date | January 1991 |
| Creators | Lu, Y. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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