Temperature controlled three-stage catalytic dehydrogenation and cycle performance of perhydro-9-ethylcarbazole

Organic liquid heteroaromatic compounds, e.g. 9-ethylcarbazole, are potentially promising hydrogen storage materials because they can be catalytically hydrogenated and dehydrogenated at relatively moderate temperatures. In the present work, the cyclic hydrogenation of 9-ethylcarbazole and the temperature controlled stage-wise dehydrogenation of perhydro-9-ethylcarbazole were investigated. Full hydrogenation of 9-ethylcarbazole was realized over a 5 wt% Ru/Al₂O₃ catalyst at 180 °C and 80 bar, yielding a gravimetric density of 5.79 wt%. The catalytic dehydrogenation of perhydro-9-ethylcarbazole over a 5 wt% Pd/Al₂O₃ catalyst was found to undergo a three-stage process, i.e. perhydro-9-ethylcarbazole → octahydro-9-ethylcarbazole, octahydro-9-ethylcarbazole → tetrahydro-9-ethylcarbazole, and tetrahydro-9-ethylcarbazole → 9-ethylcarbazole with the initial reaction temperatures of 128 °C, 145 °C and 178 °C, respectively. Our results indicate that 9-ethylcarbazole displays an excellent cycle performance with very little capacity degradation after 10 cycles of catalytic hydrogenation and dehydrogenation. The hydrogen gas produced from the dehydrogenation possesses a high purity of over 99.99% with no carbon monoxide or other poisonous gases for fuel cells.