Struktur-Aktivit��tsbeziehung von kupferbasierten Katalysatoren in der Wassergas-Shift-Reaktion

Dissertation, RWTH Aachen University, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, RWTH Aachen University, 2021
Lean-burn engines are one of the most prevalent types of engines used in modern day vehicles. Due to the increasingly strict guidelines for their exhaust gas emissions, new systems for exhaust gas catalysis are constantly developed. However, the new systems need novel catalyst materials for proper functionality which requires a comprehensive understanding of their structure-activity relationship. Therefore, this work investigates the structure-activity relationship of copper-based water-gas shift catalysts for high temperature applications. Initially, catalysts with varying ratios of copper, zinc and aluminum were synthesized with a modified co-precipitation method and then calcined at harsh conditions to simulate ageing in an exhaust gas system. The catalyst structure showed a high dependence on their aluminum content, since a high amount of aluminum resulted in the formation of CuAl2O4-spinel structures. The formation of CuAl2O4 could be observed at temperatures as low as 400 ��C. The influence of the zinc content on the other hand was negligible for the catalyst structure and thermal stability. The reduction of the spinel-structures formed highly dispersed copper particles with specific copper surface areas up to 5 m��/gKat. Due to a close relation between the copper surface area and the CO-conversion in the water-gas shift reaction, the bulk of the catalysts outperformed an aged commercial water-gas shift catalyst, which was used as a reference. The best performing catalyst with 87 % aluminum and a 1:1 ratio of copper and zinc could reach a CO-conversion of 77 % at 250��C as well as 87 % at 350 ��C.This material was then doped with small amounts of magnesia, gold, palladium and platinum. While the doping with noble metals did not show any improvement of the catalysts, the doping with certain amounts of magnesia showed an increase in specific copper surface area. This was caused by the integration of Mg2+-Ions in the spinel structure which effectively decreases copper particle size and facilitates their reduction. At the same time, magnesia also diminished the turnover-frequency of the catalysts, so that no significant increase in CO-conversion could be observed. Based on the discussed results, various catalysts were industrially prepared by Sasol Germany GmbH and investigated in this work for their performance in the water-gas shift reaction. The resulting materials showed a high stability against thermal ageing and a high performance in the water-gas shift reaction at elevated temperatures. At 350 ��C, a CO-conversion of almost 80 % could be reached.
Published by RWTH Aachen University, Aachen