Theoretical investigation on hydrogen storage into N-ethylcarbazole catalyzed by electron-rich Ni4/TiO2-Al2O3

Liquid organic hydrogen strorage (LOHC) technique is a promising safe long-term storage and long-distance transportation at ambient conditions whose bottleneck is the development of catalyst with outstanding hydrogen storage performance and relative low cost. Here, we report a promising Ni4 clusters supported on TiO2-Al2O3 composite oxides (Ni4/TA) as the hydrogen storage catalyst. The effect of TiO2 on the geometry and electron structures of the catalyst, the adsorption behaviors of N-ethylcarbazole (NEC) and its intermediates as well as the hydrogen storage mechanism are investigated via DFT calculations. The results indicate that the electron density around the loaded Ni4 clusters accumulated and the d-band center of Ni4 cluster is modulated due to the excellent electron migration performance of TiO2 species. Thus strengthened the capture and adsorption of NEC at the active region but weakened the adsorption strength of 4H-NEC and 8H-NEC which benefit the desorption-resorption transformation process. A declination of about 60 kJ·mol−1 in the required energy for the rate controlling step demonstrate TiO2 profoundly promoted the startup of hydrogen storage reaction. Moreover, the protonation effect caused by introduction of TiO2 makes it possible to further storage hydrogen into the second aromatic ring of NEC, thus makes the fully hydrogen storage into NEC easy and controllable. This study provides a theoretical guidance for the developing of non-noble metal supported hydrogen storage catalyst with excellent performance.