Recent progress in dehydrogenation catalysts for heterocyclic and homocyclic liquid organic hydrogen carriers

Liquid organic hydrogen carriers (LOHC) are recently recognized as an attractive solution for H₂ storage and transportation. Among several challenging tasks for practical application, the most stringent limitations stem from the dehydrogenation reaction requiring high temperatures thermodynamically. Unlike previous reviews focusing on the LOHC concept, LOHC molecules, and process integration, this review highlights the state-of-the-art catalysts reported for the dehydrogenation of homocyclic and heterocyclic LOHC molecules. In the conversion of heterocyclic LOHC, Pd-based catalysts overnumbered Pt-based ones owing to preferential adsorption of heteroatoms onto the Pd surface. However, because of low stability of C-heteroatom bonds, catalyst development needs to concentrate on inhibiting the generation of byproducts while maintaining superior performance under mild conditions. In the case of homocyclic LOHC, Pt is overwhelmed in single metal and bimetallic catalysts owing to pronounced C-H bond cleavage. Nevertheless, the ability of Pt in C-C bond cleavage should be diminished for higher H2 selectivity, better catalyst stability, and steady LOHC recyclability, which is possible by tuning electronic and geometric effects of main active metals, as well as adding metal promoters. Consequently, great efforts will be diversely devoted to achieving an active and stable dehydrogenation catalyst for future LOHC demonstration.