A Perspective Review on N-Heterocycles as Liquid Organic Hydrogen Carriers and Their Hydrogenation/Dehydrogenation Catalysts

Hydrogen energy is a potential solution to the problems of global warming and resource depletion resulting from the use of fossil fuels. Liquid Organic Hydrogen Carriers (LOHCs) are a promising method for hydrogen storage, as they store and release hydrogen in liquid form. This method is environmentally friendly, compatible with existing facilities, and allows for large-scale hydrogen transport over long distances. This paper presents the hydrogenation and dehydrogenation of major N-heterocycles, such as carbazoles, quinolines, indoles, pyridines, phenazines, acridines, and naphthyridines, using traditional thermal catalysts. The catalysts are categorized as monofunctional and bifunctional catalysts. These N-heterocycles have a high hydrogen storage capacity and low enthalpy of dehydrogenation, making them more suitable for hydrogen storage than aromatics. Additionally, this text presents new photocatalysts and electrocatalysts that can catalyze hydrogenation and dehydrogenation reactions under low temperature and pressure conditions.