Yuichiro Himeda1
National Institute of Advanced Industrial Science1
Yuichiro Himeda1
National Institute of Advanced Industrial Science1
Formic acid as a liquid organic hydrogen carrier has been receiving increasing attention, due to low-toxicity, low-flammability, and biodegradability.[1] We have reported a large number of efficient catalysts for dehydrogenation of formic acid (FADH: eq. 1), which were half-sandwich iridium complexes having <i>N,N</i>-bidentate ligands, such as bipyridine and imidazoline. Toward practical hydrogen supply, robust, selective, and efficient catalysts are required. Herein, we describe the development of robust and efficient iridium-based catalysts for high pressure hydrogen production by FADH in water without any additives.<br/>HCO<sub>2</sub>H → H<sub>2</sub> + CO<sub>2</sub> (eq. 1)<br/>Recently, we have developed robust catalysts for continuous and constant hydrogen supply toward practical use.[2] The catalyst having pyridylpyrazole ligands remained catalytically active for 35 days in FADH at 70 °C to produce hydrogen gas (1.25 m<sup>3</sup>) with a TON of 10 million.<br/>Furthermore, when the reaction was carried out in closed vessel, the pressure of the evolved gases was raised. In initial studies, the catalyst generated more than 100 MPa, which was composed of H<sub>2</sub> and CO<sub>2</sub> (1:1) without CO by GC analysis.[3] Unfortunately, obvious degradation of the catalyst having 4,4'-dihydroxyl-2,2'-bipyridine ligand was observed under these conditions. The catalyst having 4,4'-diamino-2,2'-bipyridine ligand produced 157 MPa of gases from 21 M of FA solution at 80 °C.[4] It was possible to continuously produce high-pressure and CO-free H<sub>2</sub> by addition of concentrated FA.<br/><br/>[1] <i>Chem. Rev</i>. <b>2015</b>, <i>115</i>, 12936-12973; <i>Coord. Chem. Rev</i>. <b>2018</b>, <i>373</i>, 317-332; <i>Adv. Energy Mater</i>. <b>2019</b>, <i>9</i>, 1801275; ibid. <b>2022</b>, 2103799; ibid. <b>2022</b>, 10.1002/aenm.202200817.<br/>[2] <i>Adv. Synth. Catal</i>. <b>2019</b>, <i>361</i>, 289-296.<br/>[3] <i>ChemCatChem</i> <b>2016</b>, <i>8</i>, 886.<br/>[4] <i>Inorg. Chem</i>. <b>2020</b>, <i>59</i>, 4191-4199.