Lobo, AJW; (2012) Modelling Structure Direction and Morphology Control in Zeolite Synthesis. Doctoral thesis , UCL (University College London).

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Abstract

The role of the organic template has been at the centre of research into zeolite synthesis since its first inclusion in synthesis in the 1950s. Since then research has shown that the template plays many roles in the synthesis starting from ordering species in the prenucleation stage, right through to controlling the final crystal morphology. However, there currently exists no way of predicting what effects a particular template will have on either the zeolite topology or morphology. The ZEBEDDE code has been expanded to automate the building and docking processes. This allows large numbers of templates to be screened as part of systematic studies. This improved code has been used to design templates for the zeolite Boggsite. Two templates have been proposed for this role through a series of building and docking calculations starting from a methane seed. The role of the template on the morphology of zeolite crystals has been investigated. Using docking calculations, 21-crown-7 was predicted to fit well inside the cavity within zeolite L and as such may template the cancrinite columns and so promote growth in the normally frustrated a-direction. Experimental work confirmed that this was the case, and yielded crystals with a lower aspect ratio than had previously been made. The role of long chain amines on the crystal morphology of AlPO-11 was also investigated as when long chain surfactants are included in the synthesis, the length of the crystals is reduced. On the {001} and {010} surface the amine can be incorporated into the framework, but on the {001} this is not possible and so hinders growth giving the observed morphology. Building on previous work, a systematic study of the effects of some small organic templates as well as two series of diquaternary ammonium cations commonly used in synthesis has been carried out. Ab initio molecular dynamics simulations have been carried out on the templates in the presence of water. Using a code specifically written for the task, the ring structures present in the hydration layer around the template have been analysed. These ring structures have been compared to the rings found in the zeolites which they eventually form, with some links being found. This work has been supported by the Engineering and Physical Sciences Research Council, and by ExxonMobil Research and Engineering. Simulations in chapter five were possible due to computer time on the national super computer HeCTOR, provided by the Materials Chemistry Consortium.

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