Study of hydrogenation and dehydrogenation of 1-methylindole for reversible onboard hydrogen storage application

We report a new candidate of liquid organic hydrogen carrier, 1-methylindole, with a hydrogen content of 5.76 wt% and a low melting point of below −20 °C. The hydrogenation of 1-methylindole and the dehydrogenation of octahydro-1-methylindole were investigated in details. Full hydrogenation of 1-methylindole was realized over a 5 wt% Ru/Al2O3 catalyst at 130 °C and 6.0 MPa, and both conversion and selectivity of 100% towards octahydro-1-methylindole were achieved. The catalytic dehydrogenation of octahydro-1-methylindole was carried out over a 5 wt% Pd/Al2O3 catalyst. By using a combined experimental and density functional theory approach, the mechanism of octahydro-1-methylindole dehydrogenation to 1-methylindole and the two stable isomers of octahydro-1-methylindole were analyzed. The effect of reaction temperature and dosage of catalyst on the hydrogen release content were systematically studied. In addition, the dehydrogenation of octahydro-1-methylindole at 160-190 °C on Pd/Al2O3 was well described by a first-order stepwise dehydrogenation reaction with the apparent activation energy of 122.99 kJ/mol. The purity of released H2 was higher than 99.99% with no detectable impurity.