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Author
Costa Gili, Lluís
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Abstract
Among all greenhouse gases, carbon dioxide is the most produced worldwide. The reduction of this molecule into valuable products has been a hot topic in different scientific fields, where metallic organic frameworks (MOF) have been used as a catalyst for this conversion reaction. Electrochemical flow systems attract direct interest for industrial applications that are economically viable both for production requirements and valuable products. The catalyst ZIF-8 can be used for the reduction of CO2 into carbon monoxide, as several studies have proven in batch scale. This MOF can be synthesized in flow at conditions that requires low energy consumptions and obtains CO, which is a valuable product. Therefore, this thesis has aimed to synthesize modifications of ZIF-8 that could enhance the conversion of CO2 and the subsequent testing in both batch and flow systems.
Different samples were synthesized at room temperature, with no additional pressure and short reaction time, fulfilling the conditions for scale-up processes. The mentioned ZIF-8 modifications made, including size reduction and enchantment of conductivity, were successfully achieved obtaining confirmation of structure, crystallinity, and size by PXRD. Additionally, electrochemical tests were achieved in batch where a novel setup was designed to double-check the overall performance of the samples using a pressure indicator. The tests were performed in different working electrodes, where heat-treated carbon paper ensued the highest performance. Overall results showed higher conversion rates for all modified samples, being the additive-enhanced ZIF-8/ferrocene and ZIF-8/triethylamine the highest values up to 31,4 and 42,3 mA/cm2 over a 26,2 mA/cm2 for a standard ZIF-8. Furthermore, a reduction of the applied voltage necessary to start the reaction was achieved by the same samples and up to 150-175 mV.
Finally, ZIF-8 (1:8), (1:32) and ferrocene were also tested in a flow system, showing an improving with respect batch and maintaining the highest performance for the sample with additive.
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