Tailored catalysts for the synthesis of SynFuels via methanol dehydrogenation and transfer-hydrogenation

• Massgeschneiderte Katalysatoren fur die Synthese von synthetischen Kraftstoffen mittels Methanoldehydrierung und Transfer-Hydrierung

Osterthun, Ole; Klankermayer, Jürgen (Thesis advisor); Leitner, Walter (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

The use of fossil resources has to be limited in light of the scarce availability of oil in the future and the associated damages to the environment. Although fossil resources are used as feed stock in the chemical industry, the major share of fossil resources is used for energy production. Most prominently, fossil resources are used as fuels in the transportation sector. Thus, transitioning the transport sector from fossil resources to renewable resources will have a major impact on the environment. Oxymethylene ethers (OMEs) are currently investigated as a promising fuel additive. OMEs have the potential to be synthesized from renewables and further have significant advantages with regard to their fuel properties. The addition of OME to Diesel fuel leads to drastically reduced NOx and soot emissions. In this thesis, catalysts were developed for a new synthesis route of OMEs from methanol. This synthesis pathway utilizes methanol dehydrogenation to access the formaldehyde intermediate. In contrast to the oxidation of methanol, methanol dehydrogenation yields molecular hydrogen and therefore enables an advanced hydrogen management for the selective synthesis of OMEs. Catalysts for a base-free methanol dehydrogenation and transfer-hydrogenation were developed and mechanistically investigated. An iridium catalyst was designed to achieve TONs up to 204 for OME1. The use of operando NMR spectroscopy, quantum-chemical calculations and targeted experiments led to the proposition of a plausible mechanism. Ruthenium catalysts were investigated and tailored to achieve TONs up to 131 for OME1. The extensive use of quantum-chemical calculations enabled a rational design approach for the ruthenium catalysts. Quantum-chemically predicted activation and deactivation pathways were evaluated experimentally. In addition, the ruthenium catalysts showed reactivity not only in the dehydrogenation of methanol but also in a coupled dehydrogenation-hydrogenation reactions. Lastly, the concept which is developed for the noble metals iridium and ruthenium is transferred to more abundant iron and manganese catalysts. The results gained in the study of abundant-earth metals showed a general proof of concept for the synthesis of OME1 from methanol.