Hydrogenation Kinetics of N‐Ethylindole on a Supported Ru Catalyst

Abstract

With its low melting point of −17.8 °C and gravimetric density of 5.23 wt %, N‐ethylindole is a promising candidate for use as a liquid organic hydrogen carrier (LOHC). Here, the influences of reaction temperature and hydrogen pressure on the hydrogen capacity of N‐ethylindole in the liquid phase are studied. It is found that fully hydrogenated N‐ethylindole can be achieved at 190 °C within 80 min. The hydrogenation of N‐ethylindole over 5 wt % Ru/Al2O3 is found to follow first‐order kinetics with an apparent activation energy of 62.4 kJ mol−1; its rate constant is subsequently derived. The initial rate and turn‐over frequency (TOF) at 160 °C–190 °C are also calculated. The structures of the intermediates during hydrogenation of N‐ethylindole are discussed based on the results of density functional theory calculations. Finally, the hydrogenation mechanism for N‐ethylindole is established.

Fast hydrogenation kinetics of acridine as a candidate of liquid organic hydrogen carrier family with high capacity

“…Afterwards, N-propylcarbazole (NPCZ) and N-ethylindole (NEID) were investigated as LOHCs by our group. Nevertheless, the theoretical gravimetric hydrogen contents (5.43 wt% for NPCZ and 5.23 wt% for NEID) are slightly lower than that of NECZ [20,25,41] . Recently, we propose a novel LOHC compound, 2-methylindole (2-MID), which has a lower apparent activation energy compared with NECZ.…”

Heterogeneous Catalysts in N-Heterocycles and Aromatics as Liquid Organic Hydrogen Carriers (LOHCs): History, Present Status and Future

“…Pez et al effectively reduced the dehydrogenation reaction temperature and energy requirements of liquid organic hydrogen carriers by introducing heteroatoms (N, S…) into traditional aromatic compounds, opening up a very promising way for the development of organic liquid hydrogen carriers. After that, heteroaromatic compounds became a hot field of research for new organic liquid hydrogen carriers, and more and more heterocyclic compounds with a high hydrogen storage density have been developed, such as N-propylcarbazole (NPC) [ 55 , 56 ], 1-methylindole (1-MID) [ 57 ], 2-methylindole (2-MID) [ 58 ], 1,2-dimethylindole (1,2-DMID) [ 10 ], N-ethylindole (NEID) [ 59 , 60 ], 7-ethylindole(7-EID) [ 61 ], 2-(N-methylbenzyl)-pyridine (MBP) [ 62 ] and acridine (ACD) [ 47 ], etc. In addition, dibenzyltoluene (DBT), with a high hydrogen storage capacity and suitable melting and boiling points, was first used as the liquid organic hydrogen carrier by Brückner et al [ 63 ] in 2014 and has been studied since then [ 38 , 64 , 65 ].…”

Synthesis of bifunctional Ru–Pd catalysts following a double reduction method: hydrogenation/dehydrogenation of liquid organic hydrogen carriers

“…30 Therefore, another class of aromatic compounds called N-heterocycles are better candidates for LOHCs due to their lower heat of dehydrogenation and higher stability. Cheng and co-workers have primarily focused on studying aromatic heterocyclic LOHCs, such as N-ethylcarbazole (NECZ, 5.79 wt%), 31,32 N-propylcarbazole (NPCZ, 5.43 wt%), 33 N-ethylindole (NEID,5.23 wt%), 34,35 2-methylindole (2-MID, 5.76 wt%), 36 7-ethylindole (7-EID,5.23 wt%), 37 1-methylindole (1-MID, 5.76 wt%), 38 and acridine (ACD,7.25 wt%). 39 Izquierdo et al 40 investigated a series of compounds based on N-and S-heterocycles through density functional theory, and their results indicated that 1H-pyrrole/tetrahydro-1H-pyrrole and thiophene/tetrahydrothiophene can be used as candidate materials for LOHCs.…”