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The adsorption and reaction of ketones on the surface of group 10 metal catalysts, a density functional theory study

Mann, Rajinder Kaur 2004. The adsorption and reaction of ketones on the surface of group 10 metal catalysts, a density functional theory study. PhD Thesis, Cardiff University.

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Abstract

The hydrogenation of ketones over cinchona modified transition metal surfaces is an important step in many applications in heterogeneous catalysis, such as the production of unsaturated alcohols from a-0 unsaturated ketones. In the gas-phase simple ketones, such as acetone, do not have a significant population of the enol isomer. Even so deuterium exchange studies clearly point to the involvement of the enol form in hydrogenation catalysis over some group 10 metals. Two different aspects of the nature of the intermediates involved in the model enantioselective hydrogenation reaction are investigated in this work. In Chapter 5, a combined semi-empirical and ab initio conformational analysis of cinchonidine reveals four stable structures of the alkaloid, two Open and two Closed forms. The reaction energies for the formation of the diastereomeric complex between protonated cinchonidine conformers and the s-cis and s-trans isomers of ethyl pyruvate and butane-2,3-dione are used to predict the relative concentrations of these intermediates. For both reactants, the complex involving the Open(3)H+ structure with the s-cis conformation of the reactant, favouring the pro (R) lactate and hydroxybutanone are optimised to be the dominant intermediates formed in the hydrogenation reaction, providing theoretical enantiomeric excesses of 33% and 98%, respectively. In Chapters 6 and 7, periodic density functional theory calculations are used to examine the chemisorption of formaldehyde and acetone as model keto groups for the pyruvate on (111) surfaces of Pd and Pt. To test computational methods the adsorption of ethene on Pt(III) is investigated. The CASTEP program is found to overbind the ethene molecule to the surface. The corresponding adsorption energies are overestimated by between 10 and 20% when compared to analogous data generated with the VASP code. The overestimation is caused by the use of ultrasoft pseudopotentials generated at the local density approximation level. Reliable adsorption data for the chemisorption of formaldehyde and acetone is obtained with the VASP program, which uses pseudopotentials based on the projector augmented-wave model. The relative energies suggest that the Pt surface is more reactive than the Pd, and that the adsorption of the enol isomer of acetone is thermodynamically stable compared to the keto form. Small activation barriers for the favourable modes of chemisorption are calculated

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303165733
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Oct 2017 15:27
URI: http://orca-mwe.cf.ac.uk/id/eprint/55561

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