Synthesis, Characterisation and Applications of Zinc-Substituted Zeotypes

Abstract

Zincosilicate zeotypes are microporous materials that show interesting properties, particularly suitable for ion exchangin divalent cations and application in Lewis-acid reactions. The synthesis of zincosilicates with the MFI framework type was carried out exploring different methodologies and an ideal synthesis strategy was found, using KOH as the inorganic mineralising agent. Solid state NMR and other spectroscopic characterisation techniques (such as XAS and DRIFTS) revealed the structural features of the synthesised materials and confirmed the hypothesis that the addition of KOH in the synthesis gel would help heal the silanol defect sites in the framework, improving the ion exchange properties of the materials. The zeotypes were used as catalysts in chemical reactions such as methane activation (for its direct conversion into methanol) and the conversion of ethanol to acetaldehyde. For the latter, the zeotype materials showed remarkable results, with high selectivity and productivity of acetaldehyde. This work showed the potential of zincosilicate zeotype in heterogeneous catalysis, thanks to the improvement and optimisation of thei properties during the synthesis stage. Moreover, it paves the way for further studies which will explore the synthesis of zeotypes with different framework types and Lewis acid properties and the potential application in chemical reactions.