Microwave synthesis of hierarchical H-ZSM-5, H-Beta and H-Y and their catalytic applications in alkylation and Diels-Alder cycloaddition

• Main Author: McGlone, J.
• Published: University of Liverpool 2016
• Subjects: 547
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.721973

In this thesis, new methodologies in zeolite synthesis have been explored to enhance mesoporosity and, their catalytic performance in alkylation, but also in the production of bulky bio-derived aromatics via Diels-Alder cycloaddition of ethylene to 2,5-dimethylfuran. There is a growing amount of interest in the synthesis of hierarchical zeolites in catalytic transformations, with the aim of improving diffusion within pores and catalytic performance. Typically, the formation of hierarchical zeolites can be achieved by using top-down or bottom-up approaches. In this thesis, a top-down approach was first studied, whereby the post synthesis treatment of commercial and in-house prepared zeolites are carried out using alkaline conditions to remove silicon and therefore, enhance mesoporosity. Furthermore, a bottom-up approach was also explored and a hard template used to generate mesoporosity during the synthesis of the zeolite. In both approaches, we have studied and optimised synthetic conditions with the utilisation of microwave reactors. Firstly, the optimum conditions used for the alkaline treatment for H-ZSM-5 were applied to commercial and home-made H-ZSM-5, H-Beta and H-Y with varying SiO2/Al2O3 molar ratios. We report the microwave synthesis of H-ZSM-5, H-Beta and H-Y zeolites with a synthesis time of 14 hours or less. We found that desilication was effective at increasing pore size at the mesoporous range as measured by nitrogen adsorption-desorption, although the higher the desilication the higher the loss in crystallinity. Desilication resulted in an increased acid site density in H-ZSM-5, whereas a reduction of acid site density was observed for desilicated H-Beta and H-Y, as determined by temperature programmed desorption. Hierarchical H-ZSM-5, H-Beta and H-Y prepared by post synthesis treatment were tested in the Friedel-Crafts alkylation of benzyl alcohol. Interestingly, at the range of reaction conditions studied, not all of the zeolites showed enhanced activity after desilication and this is discussed on the basis of changes in the acid site density. However, with alkaline treated H-Y nearly 20% greater catalytic activity was attained.