Study of catalytic hydrogenation dehydrogenation on an alternative LOHC: 4-methylindole

The liquid organic hydrogen carriers (LOHCs) system has attracted much attention because of its promising characteristics. In this paper, 4-methylindole (4-MID), was selected and studied in hydrogenation and dehydrogenation processes as a potential liquid organic hydrogen carrier (LOHC) because of its theoretical hydrogen storage density of 5.76 wt%, a melting point of 5 °C and a boiling point of 267 °C. Full hydrogenation of 4-MID was carried out over a 5 wt% Ru/Al₂O₃ catalyst in the range of 160–200 °C at 7 MPa. The results showed that the hydrogenation reaction rate was positively correlated with the temperature, and the apparent activation energy was 67.3 kJ/mol. The structure of the hydrogenation intermediates was calculated to determine a reasonable reaction pathway by means of Material Studio calculations. The full hydrogenation product, was dehydrogenated over a 5 wt% Pd/Al₂O₃ catalyst in the range of 150–180 °C at 101 kPa. The fully dehydrogenation was accomplished at 150 °C for 70 min. The cycling performance of 4-MID was investigated and it was found that after three cycles, its hydrogenation and dehydrogenation performance was good.