Structure, bonding and catalytic activity of modified mesoporous silicates

Dixon, J.M., 2004. Structure, bonding and catalytic activity of modified mesoporous silicates. PhD, Nottingham Trent University.

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The family of mesoporous silicates designated M41S are a relatively new development in the field of catalysis, having been introduced to the scientific community by scientists from Mobil in 1992. They possess the novel physical property of a uniform pore size, which can be tailored over a wide range of diameters with narrow size distributions.

The scope for the use of mesoporous materials in catalysis is great, since it opens up areas such as pharmaceutical and fine chemical production; where traditional molecular sieves have a limited application because of their small pore size compared to reactant molecules.

However these materials are chemically rather inactive; so have little scope for catalytic applications in the absence of chemical modification. Strategies for modifying these materials range from the inclusion of metal ions; to bestow acid, base or redox properties, to the production of inorganic/organic hybrid materials, which can be functionalised through the organic species.

The focus of this work is MCM-41, a member of the M41S family with hexagonally arranged, unidirectional, non-intersecting, cylindrical, pores. Modification strategies here include the incorporation of aluminium, one of the earliest attempted methods to instil acidity in the materials, and a study of the effects of inclusion on physical and chemical properties. Aluminium-containing materials have been tested in the acylation of anisole with acetic anhydride, and the structural effects of aluminium investigated. Although the materials are, to some extent, active in this reaction, significant effects on pore structure have been observed.

Incorporation of iron, both synthetically and by post-synthetic modification, has been explored. In addition to the possibility of creating a redox active material this has allowed for examination of the similarities and differences between iron incorporated by the different routes. The redox behaviour of samples has been investigated and their catalytic activity in carbon monoxide oxidation established. Samples with iron incorporated synthetically and post-synthetically, somewhat surprisingly, display very similar redox behaviour, despite some evidence that the location of the iron species is different.

Additionally a number of inorganic/organic hybrid materials have been produced, by a very simple method, and investigated. The nature of the organic attachment appears to affect the stability of the resultant material and the effects on the pore void of the MCM-41. Functionalisation of hybrid material has been attempted, with little initial success, but the remarkable stability of one of the resultant materials is, in itself, interesting because MCM-41 is known to have little hydrothermal or long-term stability.

An integral part of this project was to design and build a piece of apparatus for temperature-programmed desorption, and the development of this is also reported here; although few results of the use of this equipment are included in the project.

Item Type: Thesis
Creators: Dixon, J.M.
Date: 2004
ISBN: 9781369316155
Divisions: Schools > School of Science and Technology
Record created by: Linda Sullivan
Date Added: 25 Sep 2020 13:10
Last Modified: 23 Aug 2023 12:54

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