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Title: Alkyne coupling reactions on palladium catalysts
Author: Collings, M. P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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The chemistry of the simple alkyne compounds ethyne (acetylene), propyne (methylacetylene) and 2-butyne (dimethylacetylene) over various palladium catalysts has been studied. Both UHV experiments with single crystal surfaces and microreactor experiments with zeolite supported palladium clusters were performed. A particular emphasis was placed on coupling reactions - the bonding of two or more alkyne molecules. The adsorption and chemistry of propyne on Pd(111) and Au/Pd(111) alloy surfaces has been studied in detail using XPS, AES, LEED, UPS and TDS. Close reference to is made to the chemistry of ethyne on these surfaces, which has been previously investigated. The adsorption configuration of propyne closely resembles that of ethyne. Molecular desorption of propyne is the most efficient process, although coupling to benzene, hydrogenation of propene and decomposition represent significant reaction pathways. Cyclotrimerisation of propyne to trimethylbenzene is activated over Au/Pd(111), but the efficiency of this reaction is much lower than the analogous reaction of ethyne. A less detailed investigation of 2-butyne chemistry provided further comparative data. The adsorption configuration adopted by 2-butyne is more distorted than that of ethyne and propyne. 2-butyne is inactive for coupling on both Pd(111) and Au/Pd(111) alloys. The formation of toluene and xylene by mixed coupling reactions of various combinations of ethyne, propyne and 2-butyne was observed over Au/Pd(111). Formation of tetramethylbenzene and larger methyl benzene products was not observed. Several possible heterocyclic coupling reactions of propyne were investigated, but of these, only the addition of oxygen to form dimethylfuran was observed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available