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Abstract:

Zeolites are microporous aluminosilicates with a fixed pore opening in the range of small molecules such as CO2 or methane. Additionally, their inner environments can be finetuned by ion exchange or by alterations in chemical composition making them an outstanding candidate for catalysis and adsorption and a key material offering technological solutions to current challenges surrounding us such as climate change and resource scarcity. To tune them for specific industrial applications, a certain degree of flexibility in properties is expected. However, since zeolite crystallization is a kinetic process, any changes in the composition of the synthesis medium might result in unexpected outcomes. In this work, the focus lies on trying to control two zeolite properties: the Divalent Cation Capacity (DCC) and the Si/Al ratio.. The Si/Al ratio is a measure of how much Al is present in the zeolite, whilst the DCC is a measure of the location these Al atoms take with respect to each other, and these can be directly correlated to catalytic activity. Classically, the control of DCC occurred through two routes: kinetic control and thermodynamic control. In this work an attempt was made to combine these two distinct routes through the addition of alkali cations to an interzeolite conversion of FAU-to-CHA. This method was successful and the DCC was increased to the theoretical maximum, which provides exciting opportunities for transition-metal chemistry. To increase the range of zeolite compositions IZC can provide, a new synthesis procedure, named split synthesis was developed. Unlike conventional syntheses, where there are no changes in batch composition after the synthesis has started, split synthesis introduced mid-synthesis compositional changes by addition or removal of materials at the moment the starting source has fully dissolved. Using this new method, we synthesized SSZ-13 zeolites which lie well outside of the usual synthetical range. Rapid synthesis of sub micrometer-sized, high-silica SSZ-13 zeolites (up to a Si/Al of 180) was achieved in hydroxide medium. These materials showed themselves to be excellent candidates for the reduction of CO2 to olefins when mixed with a ZnZrOx co-catalyst, reaching an olefin to paraffin ratio of 2.6, which is approximately 5 times higher than the reference SSZ-13 (Si/Al of 15). In a second stage, the materials synthesized in this work were subjected to testing in gas separation, both as a filler in mixed matrix membranes and through inverse gas chromatography, a technique to study adsorption. During the investigation of the effect of DCC on the adsorption of alkanes, no considerable impact was observed due to the high Si/Al of the zeolites. However, to our surprise, it was discovered that Na exchanged zeolites that were synthesized using Mi didn't display catalytic reactivity during adsorption testing, in contrast to their counterparts that were made in a Li-free environment. By probing the zeolites using infrared spectroscopy, it was found that Li can passivate the weakly acidic silanols responsible for the catalytic activity. This result has great implications as it could be used as a (post-)synthetic route to reduce side reactions in acid-catalyzed zeolite chemistry. In a final chapter, AEI type zeolites were utilized as a filler material for mixed-matrix membranes, which could improve membrane performance. The Na-SSZ-39 mixed matrix membranes are the first ever polymer-based membranes that are able to compete with inorganic pure zeolite membranes in permeance and selectivity yet offer the great benefit of easy production and flexibility.