Comparative Study of Catalytic Hydrogenation of 9-Ethylcarbazole for Hydrogen Storage over Noble Metal Surfaces

Abstract

The use of liquid organic hydrides (LOH) as a chemical hydrogen store to supply hydrogen gas for a polymer electrolyte membrane fuel cell (PEFC) is explored. In the present work, hydrogenation of 9-ethylcarbazole is particularly investigated in the liquid phase over different unsupported noble metal powders. The kinetics obtained from the hydrogenation of the substrate over these catalytic systems are modeled, and the derived fundamental rate constants are systematically compared. It is found that the differences in activity and product distribution of the reaction over different metal surfaces depend critically on the electronic structures of the metals. From the prospective application of 9-ethyl-carbazole, an effective catalyst should be able to convert the substrate to the fully hydrogenated cis product without forming any kinetically stable intermediates. Ruthenium is the most active catalyst among all the metals studied for this reaction. However, this catalyst suffers from relatively low selectivity with the accumulation of large quantities of partially hydrogenated intermediates due to weak adsorption and poor surface diffusion of the intermediates for further hydrogenation.

Catalytic hydrogenation and dehydrogenation of N-ethylindole as a new heteroaromatic liquid organic hydrogen carrier

“…In particular, no kinetically stable intermediates were produced over the Ru catalyst. This is in contrast to the case of N-ethylcarbazole hydrogenation, in which intermediates, such as 8H-NECZ, were found to be kinetically stable on various noble metal catalysts [30,31]. From the measured products distribution, the apparent activation energy for the consumption of NEID was derived to be 62.4 kJ/ mol, based on the kinetics model used in Refs.…”

Model Catalytic Studies of Novel Liquid Organic Hydrogen Carriers: Indole, Indoline and Octahydroindole on Pt(111)

“…[8] For instance, N-ethylindole [8a] and 2-methylindole [8b] have hydrogen storage capacities of 5.23 and 5.76 wt %, respectively,a nd full hydrogenation was achieveda t1 60 8Co ver 5wt% Ru/Al 2 O 3 within 80 and 40 min and at 90 and 70 bar H 2 ,r espectively.D uring hydrogenation, 2H-and 4H-indole derivatives are formed as intermediates. [9] Ap articularly appealing feature of this system is that dehydrogenation of indolinei st hermodynamically more favorable than for mosto ther hydrogen-rich LOHC compounds.A s ar esult, hydrogen can be releaseda tt emperatures as low as 1008 C, that is, closet ot he operation conditions of low tem-peraturePEM fuel cells. [9] Ap articularly appealing feature of this system is that dehydrogenation of indolinei st hermodynamically more favorable than for mosto ther hydrogen-rich LOHC compounds.A s ar esult, hydrogen can be releaseda tt emperatures as low as 1008 C, that is, closet ot he operation conditions of low tem-peraturePEM fuel cells.…”

Hydrogenation of the Liquid Organic Hydrogen Carrier Compound Monobenzyl Toluene: Reaction Pathway and Kinetic Effects

“…Studies on catalysts for hydrogenation of different LOHC materials, especially N ‐ethyl carbazole, have been published in recent years by a number of groups (e.g., Eblagon et al., Wan et al., Sotoodeh and Smith, Yang et al., and Ye et al …”