Structure / reactivity relationships in N-containing Liquid Organic Hydrogen Carrier (LOHC) systems

点击翻译按钮获取中文摘要

Among the chemical energy storage technologies aiming for storing hydrogen in hydrogen-rich solids or liquids, Liquid Organic Hydrogen Carriers (LOHC) are particular appealing as they allow for hydrogen handling in the infrastructure of today’s fuels. LOHC systems are hydrogen storage media, that consist of pairs of hydrogen-lean, typically aromatic or heteroaromatic liquids (H0-LOHC) and hydrogen-rich, typically alicyclic or heteroalicyclic liquids (Hx-LOHC). H0-LOHC stores hydrogen by an exothermic catalytic hydrogenation reaction while Hx-LOHC releases hydrogen by an endothermic catalytic dehydrogenation reaction. So far, the selection of molecules considered for the use as LOHC systems was very much driven by practical and engineering considerations. Questions like “is it available in large quantities?”, “is it robust enough?”, “is it cheap enough?”, “what about ecotoxicity?” have largely dominated the selection process. Consequently, a relatively small number of different molecules have been investigated so far in greater detail. The obviously very relevant quest for “the ideal LOHC pair” on purely fundamental scientific grounds has not been taken place so far. In particular, the potential of modern, computational chemistry in combination with state of the art analytics, surface science and “real” catalytic studies has so far not been applied to find better LOHC molecules for hydrogen storage in reversible hydrogenation/dehydrogenation cycles. In this project, we aim to develop and evaluate nitrogen-containing LOHC systems based on the fundamental understanding of the structure / reactivity relationship in the heterogeneous dehydrogenation reaction using model surfaces and model substrates. The new molecules will be selected based on a pre-screening by computations for their specific functionality and the most favorable thermodynamics and kinetics. These properties will be combined with chemical robustness to allow for repeated charging and release cycles. Target Hx-LOHC molecules will enable, for example, extremely low dehydrogenation temperatures, high durability in hydrogenation / dehydrogenation cycles combined with very low melting points. This will be realized by a proper choice of functionality and geometry of the selected molecules. Thus, a knowledge-based development of hydrogen storage compounds with enhanced performance is targeted.