Hydrogen storage and release performances of N-heterocyclic hydrogen storage carriers

N-heterocycles are considered to be the most promising liquid organic hydrogen carriers due to the relatively low dehydrogenation reaction enthalpy. In this study, the hydrogen storage and release properties of five common N-heterocyclic hydrogen storage carriers were investigated using commercial catalysts. A commercial Ru/Al₂O₃ catalyst was used to evaluate the hydrogenation performance of poor hydrogen N-heterocycles, while a commercial Pd/Al₂O₃ catalyst was used to assess the dehydrogenation performance of perhydro-N-heterocycles. During the dehydrogenation process at 180℃ for 6h, the conversion rates of 12H-N-ethylcarbazole, 8H-indole, and 8H-N-methylindole were 96.54%, 61.98%, and 75.11%, and dehydrogenation rates of 79.88%, 30.15%, and 54.47%, respectively. After reaction 6h at 200℃, the conversion rates of 10H-quinoline and 10H-2-methylquinoline were 4.92% and 44.42%, with dehydrogenation rates of 3.22% and 35.35%, respectively. The results indicate that the N-ethylcarbazole system exhibits excellent dehydrogenation efficiency, while the N-methylindole system shows good hydrogen storage and release activity, and all materials remain liquid at room temperature, which is favorable for practical applications. The quinoline system has a high hydrogen storage density, but its storage and release conditions are relatively harsh and require further research and optimization. This study provides a reference for the selection of N-heterocyclic hydrogen storage carriers and an evaluation method for hydrogen storage and release performance.