Long-Term Hydrogen Production from a Methanol-Water Solution Catalyzed by an Iridium Complex

Long-term hydrogen production from a methanol-water solution was achieved by developing a new reaction system employing a homogeneous iridium catalyst bearing a bipyridonate-type functional ligand. By optimizing the methanol:water ratio of the reaction solution, the efficiency of hydrogen production was greatly improved in relation to that reported in our previous studies. Additionally, the effect of the scale of reaction was investigated. It was found that a small-scale reaction led to a longer lifetime of the iridium catalyst, accomplishing long-term continuous hydrogen production at a constant rate for over 500 h. Furthermore, procedures for catalyst reuse were studied. After hydrogen production for 400 h, all volatiles in the reaction system were removed under vacuum. This simple procedure is highly effective for the reactivation and reuse of the catalyst. Finally, hydrogen production (13.7 L, 562 mmol) from methanol (12.3 mL, 303 mmol) and water (5.46 mL, 303 mmol), in a continuous reaction for 800 h, was achieved.