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Surface science studies of the reaction of molecules of relevance to VAM synthesis using Pd and Pd/Au single crystal surfaces

Morgan, Christian Rory. 2005. Surface science studies of the reaction of molecules of relevance to VAM synthesis using Pd and Pd/Au single crystal surfaces. PhD Thesis, Cardiff University.

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The adsorption, reaction and decomposition of a series of molecules (oxygen, ethene, acetic acid, carbon monoxide, acetaldehyde and vinyl acetate) associated with vinyl acetate synthesis were investigated using a combination of ultra-high vacuum surface science techniques, including molecular beam sticking and temperature programmed desorption. The catalysts were annealed single crystal Pd (110) surfaces and bimetallic Au/Pd (110) surfaces prepared by metal vapour deposition and annealing. All the molecules investigated adsorbed well to Pd (110) with a high sticking probability, and mechanisms for the reactions of each with the surface were suggested. The carbonaceous organic molecules all decomposed to deposit carbon at the surface at room temperature and above, blocking active sites to adsorption. Above a specific temperature, this carbon went subsurface and no longer inhibited subsequent adsorption of molecules. A residual carbon layer was often characterised by low energy electron diffraction and spectroscopy techniques, the exact structure varied with incident molecule type. The deposited carbon could often be removed in a facile manner by oxygen treatment. In the case of acetic acid, an acetate species was formed at room temperature and decomposed at higher temperatures with autocatalytic decomposition kinetics. Vinyl acetate reacted in a similar way to acetaldehyde under most conditions investigated, suggesting vinyl acetate decomposes primarily via a cleavage that produces acetyl groups under these conditions. An exceptional case occurred at 300-323 K at high coverages, where the formation of a template structure on the surface may stabilise acetate formation from vinyl-acetate cleavage. On Au/Pd (110) surfaces after annealing, the Au was determined to be partly subsurface in most cases. The uptake and sticking probability of each molecule were reduced often in a manner approximately proportional to Au content, in broad agreement with structural data on Au/Pd(110) published elsewhere.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303203367
Funders: BP Chemicals CASE award, EPSRC
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Oct 2017 15:29

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