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Supported metal catalysts for the production of chemical precursors

Hayward, James 2013. Supported metal catalysts for the production of chemical precursors. PhD Thesis, Cardiff University.
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Supported metal catalysts have applications across a broad range of industrial processes. The metal species are often the active catalysts in these processes, but supporting these materials upon a different material can produce desirable characteristics in the overall catalyst. These effects can include, but are not limited to, increased dispersion of active material, increased stability of the active material, and, depending on the supporting material, beneficial metal-support interactions can be generated. The production of benzaldehyde from benzyl alcohol is a reaction with high commercial value. Gold-palladium catalysts have been shown to be effective at production of benzaldehyde from benzyl alcohol under relatively mild, solvent-free conditions. It has also been shown that the selectivity of this reaction is dependent upon the acidic or basic character of the support material. Perovskites are a class of highly stable minerals with a general formula of ABO3, with A being a cation with a larger ionic radius than B. The acidic and basic character of a perovskite is strongly determined by the nature of the A cation, which allows for the possibility of adjusting this character by metal substitution. This study investigates the effects of gradual substitution of lanthanum for strontium in vanadate perovskites, and showed that incorporation of the substituted metal is effective up to a certain point, beyond which the material switches to two spate perovskite phases. The substitution of the metal ions was shown to have an effect on the acidic and basic properties of the perovskite materials using the Isopropyl Alcohol (IPA) reaction, which forms different products on acidic or basic sites. Following this, substitution with a wider range of group II metals was investigated and tested, both in the IPA reaction and as supports for precious metals in the production of benzaldehyde. A separate series of investigations were performed on Fischer-Tropsch (FT) catalysts. Fischer-Tropsch is a name given to a wide range of catalytic processes involving the production of hydrocarbons from a mixture of carbon monoxide and hydrogen, known as syngas. The formation of products is generally believed to proceed through a chain-lengthening process using single-carbon units. This leads to a broad distribution of products Abstract as opposed to a single highly selective product, and the selectivity pattern is often described using the Shulz-Florey-Anderson distribution. Much of the work on FT catalysts is involved in modifications of the catalyst system to produce a tighter distribution of products. In this study a series of investigations have been made into the effects that variations of the preparation method of CoMnOx supported on activated carbon. The basic preparation is an impregnation method, and several changes in catalyst activity and selectivity were observed following changes to this. An investigation into the effects of altering the amount of manganese relative to cobalt in the system also highlighted several trends, leading to a greater understanding of the factors affecting the conversion and selectivity of the catalyst system. A separate are of research in FT-style reactions is the production of alcohols from syngas, typically at higher pressures. As in the previous section, these an attempt was made to improve the activity and selectivity of these catalysts by alterations to the preparation methods, and also by alteration of the amount of secondary metal relative to cobalt. The catalysts used in these investigations consisted of CoMoOx supported on activated carbon. The standard preparation used a coprecipitation method based upon a similar method used for the production of CoMoS2 catalysts, which were also investigated in this study. Later investigations, notably those in which the amount of molybdenum relative to cobalt was altered, were prepared using an impregnation method. A series of improvements to a base catalyst were achieved by alteration to the preparation conditions, but more substantial improvements were observed when the alteration of the metal ratios was investigated. With regards to the use of activated carbon as a support material, it was also observed that it was possible to bring about the reduction of the cobalt species, and to a lesser extent the manganese and molybdenum species, by heating the catalysts to a high temperature in an inert atmosphere, namely helium.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 05:48

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