The effect of the N atom on the dehydrogenation of heterocycles used for hydrogen storage

The effect of the N atom on the hydrogen release rate from heterocyclic compounds was studied by comparing the dehydrogenation rate of dodecahydro-N-ethylcarbazole, dodecahydrocarbazole and dodecahydrofluorene. Over a 5 wt% Pd/C catalyst, hydrogen recovery was fastest (TOF ∼60 min−1 at 443 K and 101 kPa) from dodecahydro-N-ethylcarbazole and ∼3 times faster than that of dodecahydrocarbazole. Dodecahydrofluorene dehydrogenation was the slowest among the compounds examined, with less than 1 wt% H2 recovered after more than 20 h at 443 K, although selectivity to the completely dehydrogenated product was 95%. Despite catalyst poisoning by the N in dodecahydrocarbazole and its dehydrogenated product, the presence of the N in the heterocycle increased the dehydrogenation reaction rate compared to dodecahydrofluorene, demonstrating that heterocycles are better candidates for H2 storage than polycycles.

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► H2 recovery rates from heterocycles is reported on a Pd/C catalyst.
► H2 recovery from dodecahydro-N-ethylcarbazole is faster than from dodecahydrocarbazole.
► H2 recovery from dodecahydrocarbazole is faster than from dodecahydrofluorene.
► The presence of the N atom in the heterocycle increases the dehydrogenation rate.