Entwicklung von festen, molekularen Katalysatoren auf Basis von Phosphor- und Stickstoff-funktionalisierten Polymeren für die selektive Umsetzung von $CO_{2}$ zu Ameisensäure, Methylformiat und Methanol

Kann, Anna; Palkovits, Regina (Thesis advisor); Pich, Andrij (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

In this thesis, solid molecular catalysts were investigated in the hydrogenation of CO2 to selected products. For this purpose, phosphorus- and nitrogen-based polymers with varying steric and electronic properties were synthesized. The catalysts were obtained by coordinating metal complexes to these polymers. In the hydrogenation of CO2 to formic acid with inorganic bases or amines, immobilized Ru catalysts based on P-polymers showed the highest activities. After a systematic variation of the reaction parameters, maximum TONs of 13,170 in K2CO3 and of 8,430 in aqueous 60 vol.% NEt3 for the catalyst Ru@P2 based on the dppe ligand were obtained. In addition, the recycling of the catalyst was demonstrated and the change of the catalytically active species during the reaction was investigated. In the base-free hydrogenation of CO2, formic acid was selectively formed with Ru catalysts based on P-polymers, achieving activities lower than in the presence of bases. In order to demonstrate that formic acid is applicable as H2 storage medium, the decomposition in the presence of amines was investigated using model solutions. In addition, the decomposition was coupled with the synthesis in the same reaction system. Ru catalysts based on P-polymers showed selective conversion of formic acid to CO2 and H2 in NEt3 and achieved high conversions. The product range was extended to methyl formate. Here, the hydrogenation of CO2 to formic acid and the subsequent esterification with methanol were combined in one step. With immobilized Ru catalysts based on P-polymers, the simultaneous formation of formic acid and methyl formate was observed. A systematic variation of the reaction parameters was performed and the recyclability of the catalyst was demonstrated. The hydrogenation of CO2 to methanol was investigated by selecting studies with high yields as starting point. In the direct conversion of CO2 and indirectly via cascade reactions with additives, the formation of methanol with Ru@P2 was not observed. Alternatively, the conversion of CO2 intermediates was considered. Starting from formic acid, the formation of methanol was detected. N-polymers with Ir as active component achieved the highest activities.

Institutions

• Department of Chemistry [150000]
• Chair of Heterogeneous Catalysis and Technical Chemistry [155310]