Katalytische Hydrierung von Kohlenstoffdioxid mit Mangan-Komplexen : Konzeption und Mechanismus

Kuß, David Alexander; Leitner, Walter (Thesis advisor); Neese, Frank (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

In this thesis the development of a system for the homogeneously catalysed hydrogenation of CO2 to methanol based on manganese complexes and the elucidation of the underlying reaction mechanism is presented. In Chapter 1, the current state of research on the hydrogenation of CO2 to methanol with transition metal complexes and the latest developments for 3d metal complexes such as manganese are presented. In addition, literature known mechanisms for the hydrogenation of carbonyl groups are presented along with computational chemistry methods for their exploration. In chapter 3.1, the suitability of a Mn-pincer complex for the hydrogenation of CO2 to methanol via the formate ester route is investigated. A particular focus is put on the identification of hindering factors, such as the characterization of potential resting states of the reaction and their elimination by the addition of additives. The designed system for methanol synthesis from CO2 is optimized in chapter 3.2 by varying all relevant reaction parameters and testing structurally related catalysts, additives, and alcoholic media.Subsequently, mechanistic aspects of the designed reaction are investigated experimentally in chapter 3.3. Atomic-scale processes are considered via isotopic labelling or stoichiometric reactions at the NMR scale, and kinetic data is collected via the kinetic isotope effect and a concentration-time profile. Finally, the experimental activation energy is determined in an Eyring-Auftragung. In the following chapter 3.4, the reaction network is investigated using the optimal computational chemistry methods at DFT and DLPNO-CCSD(T) level to find the minimal energy pathway and thus the intermediates and transition states that determine the activity. Based on these results, the calculated energy span is determined and a simplified kinetic model is derived, allowing the simulation of a concentration profile.Finally, a reliable picture of the actual molecular mechanism in place can be postulated from the comparison between the ab-initio calculated reaction mechanism and the experimental counterparts. This serves as a basis for the systematic improvement of catalysts in the hydrogenation of CO2 to methanol through computational screening or rational design.

Institutions

• Department of Chemistry [150000]
• Chair of Technical Chemistry and Petrochemistry [154110]