Hydrogenation of the Liquid Organic Hydrogen Carrier Compound Monobenzyl Toluene: Reaction Pathway and Kinetic Effects

Liquid organic hydrogen carriers (LOHCs) are an interesting option for storing hydrogen through a reversible chemical reaction. The catalytic hydrogenation reaction was studied for the carrier material monobenzyl toluene. GC analysis was used to quantify the components occurring in a complex reaction mixture. It was shown that the hydrogenation reaction proceeds predominantly by stepwise hydrogenation of the aromatic ring. As the molecular structure of monobenzyl toluene is formally the combination of a xylene and a toluene ring, two possible reaction pathways have been evaluated: hydrogenation of the mono‐substituted side ring (toluene) and di‐substituted main ring (xylene). Intermediates for both pathways were detected during the reaction. Concerning the isomeric structure of benzyl toluene, the fastest hydrogenation was observed for the para species. Isomeric mixtures were hydrogenated the slowest. Energy storage in liquid organic hydrogen carriers (LOHC) is an interesting option. The hydrogen uptake reaction of monobenzyl toluene is studied qualitatively. Two general reaction pathways are shown for this LOHC compound. Monobenzyl toluene shows a kinetic behavior similar to model compounds like toluene and xylene. Hydrogenation of an isomeric LOHC mixture appears to be slower than hydrogenation of a pure LOHC isomer.