Kinetics of Hydrogen Uptake and Release from Heteroaromatic Compounds for Hydrogen Storage

Abstract

The kinetics of hydrogen uptake by N-ethylcarbazole and carbazole, and the kinetics of H2 release from their hydrogenated products, is reported. The hydrogenation of N-ethylcarbazole at 130−150 °C on Ru was well described by a network of first-order stepwise hydrogenation reactions. The hydrogenation of N-ethylcarbazole was significantly faster than the hydrogenation of carbazole, and in both cases, >95% selectivity to the completely hydrogenated products, dodecahydro-N-ethylcarbazole and dodecahydrocarbazole, was achieved. The dehydrogenation of dodecahydro-N-ethylcarbazole at 101 kPa and 150−170 °C, proceeded to 100% conversion of the reactant over a Pd catalyst within 1 h. However, only 69% of the stored H2 was recovered due to a low selectivity to N-ethylcarbazole. In the case of dodecahydrocarbazole dehydrogenation at 101 kPa and 170 °C over the same Pd catalyst, 28% H2 recovery was obtained due to the strong adsorption of the product carbazole on the catalyst surface that also resulted in a slower rate of dodecahydrocarbazole dehydrogenation compared to dodecahydro-N-ethylcarbazole.