Naoya Onishi

Direction to practical production of hydrogen by formic acid dehydrogenation with Cp*Ir complexes bearing imidazoline ligands

A Cp*Ir complex with a bidentate pyridyl-imidazoline ligand achieved the evolution of 1.02 m3 of H2/CO2 gases by formic acid dehydrogenation without any additives or adjustments in the solution system. The pyridyl-imidazoline moieties provided the optimum pH to be 1.7, resulting in high activity and stability even at very acidic conditions.

Efficient Hydrogen Storage and Production Using a Catalyst with an Imidazoline-Based, Proton-Responsive Ligand

A series of new imidazoline-based iridium complexes has been developed for hydrogenation of CO2 and dehydrogenation of formic acid. One of the proton-responsive complexes bearing two -OH groups at ortho and para positions on a coordinating pyridine ring (3 b) can catalyze efficiently the chemical fixation of CO2 and release H2 under mild conditions in aqueous media without using organic additives/solvents. Notably, hydrogenation of CO2 can be efficiently carried out under CO2 and H2 at atmospheric pressure in basic water by 3 b, achieving a turnover frequency of 106 h-1 and a turnover number of 7280 at 25 °C, which are higher than ever reported. Moreover, highly efficient CO-free hydrogen production from formic acid in aqueous solution employing the same catalyst under mild conditions has been achieved, thus providing a promising potential H2 -storage system in water.

Sequential hydrogen production system from formic acid and H2/CO2 separation under high-pressure conditions

Hydrogen (H2) production from formic acid (FA) is highly attractive as a sustainable energy source from the interconversion between CO2 and FA. Dehydrogenation of FA at high pressures has advantages over a reaction at atmospheric conditions for the separation of H2 and CO2 due to the reaction and the volumetric energy density of H2. We demonstrated the continuous production of high-pressure H2 by catalytic decomposition of FA, and subsequent separation of H2 and CO2 from FA decomposition gas (H2 : CO2 = 1 : 1) using the phase change phenomenon at low temperatures while maintaining high pressure. An iridium aqua complex coordinated with a bidentate pyridyl-imidazoline ligand catalyzed the dehydrogenation of FA with high efficiency at a pressure as high as 153 MPa. The Ir catalyst was found to be stable under continuous addition of neat FA at high pressures. The generation time and rate of high-pressure H2 were controlled by feeding neat FA to the aqueous reaction system. Using our combined system, more than 99 mol% of H2 (96 mol% of purity) and 94 mol% of CO2 (99 mol% of purity) were separately obtained from FA as a gas and liquid, respectively, under the high-pressure conditions without any mechanical compression.

Picolinamide-Based Iridium Catalysts for Dehydrogenation of Formic Acid in Water: Effect of Amide N Substituent on Activity and Stability

To develop highly efficient catalysts for dehydrogenation of formic acid in water, we investigated several Cp*Ir catalysts with various amide ligands. The catalyst with an N-phenylpicolinamide ligand exhibited a TOF of 118 000 h-1 at 60 °C. A constant rate (TOF>35 000 h-1 ) was maintained for six hours, and a TON of 1 000 000 was achieved at 50 °C.