Advanced Zeolite Characterisation Methods to Investigate the Methanol-to-Hydrocarbons Reaction

Abstract

In this thesis the methanol-to-hydrocarbons process over zeolite catalysts has been studied using advanced zeolite characterisation methods. The methanol-to-hydrocarbons process is of great interest as it can provide an alternative route for the production of feedstocks for plastics, such as ethylene and propylene. Challenging is the deactivation of the zeolite catalyst by the formation of coke molecules and the variety of reaction products. This thesis has been divided into two parts. In part I, in-situ, ex-situ and operando techniques are used to analyse the formation of carboncontaining reaction intermediates as well as coke deposits in zeolite catalysts. Firstly, different metals were introduced to zeolite structures to enhance the catalytic performance. With operando UV-vis spectroscopy the reaction intermediates were followed and linked to the catalytic performance. It was discovered for small-, medium-, and large-pore zeolites the introduction of Mg leads to an enhanced propylene selectivity by reducing the formation of aromatic intermediates, while Zn leads to the enhanced selectivity of ethylene by the enhancement of aromatic intermediates. Secondly, large zeolite crystals were synthesized to study the intermediate products and coke formation on the microscale using microscopic techniques. Furthermore, the deactivating coke molecules can also be removed by regeneration processes, which was also studied under operando conditions. It was proposed, using this method as proof, that the methanol conversion happens in a similar manner over small- and medium-pore zeolites. In part II, the APT technique has been further developed as a key-tool to study the zeolites on the nanoscale. Using this method, the nanoscale coke distribution in small-pore zeolites was compared to medium- and large-pore zeolites. Additionally, the distribution of Mg was studied in small-pore zeolite SSZ-13 and the nanoscale Mg and coke distribution were found to be heterogeneous and clusters of Mg and carbon were found. Lastly, the distribution of Al in zeolite Beta has been found to be heterogenous at the nanoscale. The distribution of carbon and Al in zeolite Beta was found to be heterogeneous on the micro- and nanoscale.