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An overview of the kinetics and catalysis of hydrogen storage on organic liquids


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The potential for chemical H2 storage on liquid organic hydrogen carriers (LOHCs) has focused attention on the catalytic reactions needed to store and release H2 from the LOHCs. Herein we review our recent studies on the use of N-ethylcarbazole and carbazole as LOHCs. Experimental data show that the hydrogenation reactions are relatively facile, although N-ethylcarbazole hydrogenates 10×'s faster than carbazole on a 5 wt% Ru/Al2O3 catalyst at 150°C. Dehydrogenation of dodecahydro-N-ethylcarbazole is more difficult than hydrogenation and is structure sensitive on Pd catalysts. Maximum activity and 100% selectivity to the completely dehydrogenated product, N-ethylcarbazole, was achieved over a 4 wt% Pd/SiO2 catalyst with dPd ∼ 9 nm. The dehydrogenation TOF of dodecahydrocarbazole and dodecahydrofluorene were much lower than dodecahydro-N-ethylcarbazole. DFT was used to identify the dehydrogenation mechanism and explain the experimental observations. Both theoretical and experimental results lead to the conclusion that dodecahydro-N-ethylcarbazole is a better H2storage candidate than dodecahydrocarbazole.