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Title: Characterisation of new molecular sieves
Author: Hampson, Brian
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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A general introduction to zeolites and aluminophosphate based molecular sieves is followed by a more detailed review of EU-1 and AlPOj-S, the two molecular sieves studied in this work. The synthesis and characterisation of these molecular sieves is described. The characterisation techniques gave details of the framework structure and composition, surface area, and morphology. A time study of the crystallisation of AlPO4-5 from an aluminophosphate gel containing two organic templates showed the formation of a hydrate phase before the AlPO4-5 phase, the change in pH during hydrothermal crystallisation, and the transformation of the Kaiser alumina spheres to give the spherical morphology of A1PO.4-5 associated with this synthesis procedure. Volumetric adsorption and subsequent desorption of but-n-ene isomers on both molecular sieves at room temperature showed that some strong adsorption of the molecules occurs, which could be removed at higher temperatures. The effect was more pronounced with EU-1. Gravimetric adsorption of various organic compounds on AlPO4-5 showed pore filling values and rates of uptake consistent with the kinetic diameters of the organic molecules. The Langmuir model, found to give the best fit for the adsorption isotherms, was seen to break down at mid-range values of P/P0. Thermal desorption of pyridine from H-EU-1 showed that the acid sites probably exist in or close to the side pockets in the EU-1 channel system, and that a side pocket may contain more than one acid site. The A1PO4-5 samples of spherical morphology were found not to have strong acid sites. The framework of calcined A1PO4-S was seen to be degraded to a denser phase by aqueous salt solutions, whereas as-synthesised samples remained intact The extent of the attack was dependent upon the anion and the solution concentration. A1PO4-11 and AlPO4-25 samples were also attacked but to a lesser extent. EU-1 and A1PO4-S samples acted as acidic catalysts in the isomerisation of but-1-ene. Only but-1-ene, cis and trans but-2-ene were observed in the gaseous phase. A strongly bound residue was detected on the surface of EU-1 by TGA. This residue was seen to deactivate the catalyst in the first instance, but heating the sample with the residue in a vacuum was seen to change the catalytic nature of the zeolite. The activity of the A1PO4-5 samples was lower than EU-1 under identical conditions. However, samples of the AlPO4-5 spheres were seen to have a higher activity than the usual barrels. Investigations gave no solid evidence for the seat to this increased activity, but it is thought that framework defect sites may be responsible.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available