Unveiling the Potential of Heterogeneous Systems for Reversible Hydrogen Storage in Liquid Organic Hydrogen Carriers.

Transitioning towards a carbon-free economy is the current global need of the hour. The transportation sector is one of the major contributors of CO emissions in the atmosphere disturbing the delicate balance on the Earth, leading to global warming. Hydrogen has emerged as a promising alternative energy carrier capable of replacing fossil fuels, with advancements in systems facilitating its storage and long-distance transport. In this context, the concept of liquid organic hydrogen carriers (LOHCs) is taking the lead, offering a plausible solution because of its compatibility with the existing gasoline infrastructure, while eliminating the challenges associated with the conventional hydrogen storage methods. Key LOHC systems, such as methylcyclohexane/toluene and H-18-dibenzyltoluene/dibenzyltoluene (H-18-DBT/DBT), have been extensively researched for large-scale applications. However, challenges persist, particularly concerning the endothermic nature of the reactions involved. In this regard, of particular interest are the multifunctional heterogeneous catalysts supported on a single support, offering cost-effective and energy-efficient solutions to circumvent issues related to the endothermicity of the reactions. In this review, solid heterogeneous catalysts that have been developed and investigated for reversible dehydrogenation and hydrogenation reactions have been presented. These catalysts include monometallic, bimetallic, and pincer complexes supported on materials designed for efficient hydrogen uptake and release.