The Role of the Support in Heterogeneous Catalysis

Buchanan, Douglas A (1972) The Role of the Support in Heterogeneous Catalysis. PhD thesis, University of Glasgow.

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The catalysed hydrogenation of buta-1,3-diene has been studied using deuterium as a tracer over alumina- and boehmite-supported gold and silica-supported copper catalysts. The physical nature of the gold catalysts were examined by ultraviolet spectrocopy, electron microscopy and X-ray diffraction techniques. The kinetics and variation of the butene distribution with i) conversion, ii) inital 'hydrogen' pressure and iii) temperature have been investigated over each catalyst and mechanisms are proposed which are consistent with the experimental results. Preferential formation of but-l-ene is observed but the trans-but-2-ene : cis-but-2-ene ratio is 1 : 2 over the supported gold catalysts whereas over the silica-supported copper the ratio is 1 : 1. It is concluded that butadiene adsorbs as a mono-pi-bonded complex which rapidly undergoes further adsorption to the di-pi-bonded species. The resonance energy of stabilisation associated with the anti di-pi-adsorbed complex is thought to be important in determining the trans : cis ratio over the supported gold catalysts. In the initial stages of reaction separate 1,2- and 1,4-addition processes are thought to be responsible for the formation of but-1-ene and the but-2-ene, respectively, although at high conversion it is suggested that isomerisation, over the supported gold catalysts, occurs by an abstraction-addition mechanism. The variation of the deuterium distribution with i) conversion, ii) initial deuterium pressure and iii) temperature was determined mass spectrometrically. Over Au/Boehmite the do-species is most abundant whereas over Au/gamma-alumina the predominant product is the d-1-species. It is postulated that hydrogen migrates from the support to active sites on the metal and hence the nature of the support is reflected in the deutero-content of the butenes. The source of this hydrogen is believed to be water associated with the lattice of the support. Over silica-supported copper the surface coverage of adsorbed deuterium is shown to be greater than over the supported gold catalysts. Prom the results obtained it appears that the support does not play a significant role in the hydrogenation reaction over supported copper catalysts.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1972
Depositing User: Enlighten Team
Unique ID: glathesis:1972-78614
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:08
Last Modified: 30 Jan 2020 15:08

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