Heterogenous catalysis of some isomerisation processes

• Main Author: Johns, Charles Henry
• Published: University of Surrey 1956
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751488

It is now generally accepted that in the majority of heterogeneously catalysed reactions, chemisorption of one or more of the reacting species occurs. Experimental evidence has led to the conclusion that during these reactions, molecules are disrupted so that bonds may be formed between adsorbed molecules and the surface. In this Thesis, further evidence has been obtained to show the occurence of bond fission produced by the adsorption of hydrocarbons on surfaces. An experimental study has been made of the heterogeneous catalysis of some isomerisation,dehydrogenation,polymerisation and isotopic exchange reactions of four pure hydrocarbons(2-phenyl-butane, 3-methyl-hexane,(+) d limonene and cis decalin), at temperatures below 300°C. Under these conditions,only charcoal catalysts (and in the case of limonene,silica-gel and palladium) produce measurable extents of isomerisation or amounts of reaction products. Optically active 2-phenyl-butane and 3-methyl-hexane undergo simple racemisation on charcoal; a small amount of material of higher molecular weight (in the case of 3-methyl-hexane, probably the dimer) is also produced. Cis decalin does not undergo isomerisation,but small amounts of naphthalene are produced. (+) d limonene is converted rapidly on charcoal to p. cymene, while on silica-gel it is converted rapidly to p. cymene and a diterpene (probably dilimonene); in each case, small amounts of polymeric material are also produced. dl 2-phenyl-butane and dl 3-methyl-hexane undergo deuterium-hydrogen exchange with both deuterium and deuterium oxide. On the basis of these experimental results,it is possible to draw tentitive conclusions concerning the mechanisms of reaction on the catalyst surface.