A study of solid base catalysis was conducted in three main categories,
namely condensation reactions of primary alcohols, alkylation reactions of
dihydroxybenzene and hydrogenation reactions of phenol.
Ethanol was converted into 1-butanol over alkali earth metal oxides and
modified MgO catalysts (1-20 % yield). The MgO catalyst exhibits the
highest reaction activity and 1-butanol selectivity amongst the catalysts
studied. Reaction of various possible intermediates (acetaldehyde,
crotonaldehyde, crotylalcohol, butanal) and ethanol over MgO (1 bar, 450
oC) revealed that the dimerisation reaction does not proceed primarily
through the aldol condensation reaction. The reaction is proposed to
proceed through a mechanism, previously proposed by Yang and Meng, in
which a C-H bond in the -position in ethanol is activated by the basic
metal oxide, and condenses with another molecule of ethanol, by
dehydration to form 1-butanol.
iv
A self-condensation reaction of propanol was carried out at atmospheric
pressure over MgO as catalyst. The reaction gave 2-methylpentanol and
propionaldehyde as the major products. The introduction of hydrogen
before and during the reaction enhanced the catalyst selectivity to 2-
methylpentanol. The effect of possible reaction intermediates on the
catalyst selectivity and the mechanism of the reaction were investigated
over MgO and indicated the important role of hydrogen transfer in the
reaction. The highest selectivity (69 %) was achieved in the presence of
hydrogen at 450 oC with propanol conversion of 24 %.
Condensation reactions of ethanol with butanol or propanol to higher
alcohols were carried out at atmospheric pressure over various solid-base
catalysts. The ability of ethanol to be activated at either the CH2 or CH3
units played a significant role in the formation of a wide range of long chain
alcohols. The major products observed during the reaction between
ethanol and butanol were 2-ethylbutanol, 1-hexanol and to a lesser extent
2-ethyhexanol. The main products in the reaction of ethanol and propanol
were 2-methylbutanol, 1-pentanol and butanol. Trace amounts of 2-
methylpentanol were also observed.
The vapour phase alkylation of catechol over supported cesium catalysts
gave good selectivity to guaiacol formation. The TPD studies of the
catalysts used indicated that the results can be correlated with the
presence of weak basic sites on the catalyst.
The gas phase selective hydrogenation of phenol to cyclohexanone was
investigated over palladium supported catalysts in order to clarify the
influence of the support on products distribution. High selectivities towards
cyclohexanone (about 86 %) were observed on palladium supported on
high surface area titanium oxide supports. On the basis of the TPD studies,
it has been suggested that the basic properties of the support strongly
influence the adsorption-desorption of phenol and products, and are
therefore responsible for the selectivity towards the reaction products
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/6990 |
| Date | 28 May 2009 |
| Creators | Ndou, Azwimangadzi Steven |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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