In Situ Infrared Spectroscopy Analysis of Dehydrogenation of Perhydro-N-ethylcarbazole.

The dehydrogenation mechanism of perhydro-N-ethylcarbazole (12H-NEC), a promising liquid organic hydrogen carrier (LOHC), on Pd/Al2O3 catalyst was studied by in situ FT-IR analysis. Spectra were collected in transmission mode using a 12H-NEC/catalyst/KBr mixture pellet to overcome the difficulty of introducing low-volatility 12H-NEC. A peak-deconvolution, assignment, and normalization protocol was developed to interpret the complex C─H stretching region from 3100 to 2750 cm-1. The results indicate that dehydrogenation begins at the five-membered ring and that species spectroscopically consistent with 8H-NEC accumulate at approximately 100°C. A transient spectral state observed before this accumulation is consistent with an earlier partially dehydrogenated intermediate, for which 10H-NEC is one possible structural assignment. This work provides experimental insight into the dehydrogenation mechanism of 12H-NEC under mild conditions and may guide further efforts to improve the hydrogen-storage performance of 12H-NEC-based LOHC systems.