Organic liquid hydrogen carriers (OLHC) have attracted increasing attention recently, although their energy efficiency of hydrogen storage/release by transformation of OLHC is still low. In this presentation, we describe hydrogen production by dehydrogenation of formic acid (FA) (eq. 1) using homogeneous iridium catalysts in water. HCOOH → H2 + CO2 (eq. 1) We have developed a number of half-sandwich iridium catalysts with bidentate nitrogen ligands for dehydrogenation of FA in water without any organic additives. In these catalytic systems, gases (H2/CO2 = 1/1) could be effectively produced from aqueous FA solutions. No carbon monoxide (&lt; 5 ppm) was detected in the evolved gases. We found that the catalytic performances (e.g., activity, stability) strongly depended on the structure of the bidentate nitrogen ligands. Toward practical use, we developed the robust and effective iridium catalysts having five-membered N-heterocycles. As a consequence, 1 m3 or more of gas volume was produced and a TON of 5 million or more was achieved using the iridium catalysts having five-membered N-heterocycles. In this specific experiment, complicated operations such as frequent additions of substrates or additives, or monitoring the solution system were not required. Furthermore, the gases could be released under high pressure conditions without any significant decrease in the reaction rate.

Hydrogen production by dehydrogenation of formic acid using iridium catalysts

255th National Meeting (2018)

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