Yuichi Manaka

Efficient H2 generation from formic acid using azole complexes in water

Iridium azole-containing complexes are demonstrated to catalyze the dehydrogenation of formic acid into H2–CO2 (1/1) mixtures in aqueous solution in the absence of organic additives, and with a maximum turnover frequency (TOF) of 34000 h−1 at 80 °C.

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.

Simple Continuous High‐Pressure Hydrogen Production and Separation System from Formic Acid under Mild Temperatures

A simple and continuous high‐pressure (>120 MPa) hydrogen production system was developed by the selective decomposition of formic acid at 80 °C using an iridium complex as a catalyst, with a view to its application in future hydrogen fuel filling stations. The system is devoid of any compressing system. The described method can provide high‐pressure H2 with 85 % purity after applying an effective gas–liquid separation process to separate the generated gas obtained from the decomposition of formic acid (H2/CO2=1:1). The efficiency of the catalyst lies with its high turnover frequency (1800 h−1 at 40 MPa) to produce high‐pressure H2 with a good lifetime of >40 h. Interestingly, only very low levels carbon monoxide (less than 6 vol ppm) were detected in the generated gas, even at 120 MPa.

Development of an Iridium-Based Catalyst for High-Pressure Evolution of Hydrogen from Formic Acid

Abstract A highly efficient and recyclable Ir catalyst bearing a 4,7‐dihydroxy‐1,10‐phenanthroline ligand was developed for the evolution of high‐pressure H2 gas (>100 MPa), and a large amount of atmospheric pressure H2 gas (>120 L), over a long term (3.5 months). The reaction proceeds through the dehydrogenation of highly concentrated aqueous formic acid (FA, 40 vol %, 10 mol L−1) at 80 °C using 1 μmol of catalyst, and a turnover number (TON) of 5 000 000 was calculated. The Ir catalyst precipitated after the reaction owing to its pH‐dependent solubility in water, and 94 mol % was recovered by filtration. Thus, it can be treated and recycled like a heterogeneous catalyst. The catalyst was successfully recycled over 10 times for highpressure FA dehydrogenation at 22 MPa without any treatment or purification.

Bioreactors Based on Enzymes Encapsulated in Photoresponsive Transformable Nanotubes and Nanocoils End‐Capped with Magnetic Nanoparticles

Self‐assembly of asymmetric amphiphiles containing an azobenzene unit selectively produces molecular monolayer nanotubes, which can act as solid supports for enzymes without the use of chemical cross‐linkers. Encapsulation of enzymes in nanotube channels and continuous capping of both open ends with magnetic nanoparticles allow us to construct bioreactors. Transformation of the nanotubes to nanocoils induced by the trans‐to‐cis isomerization of the azobenzene unit upon UV‐light irradiation initiates catalysis due to the appearance of multiple narrow slits functioning as size‐exclusion pathways for penetration of substrates from bulk solution. Kinetic performance of encapsulated enzymes is similar to that of free enzymes. Magnetic nanoparticles are very useful for inhibiting the release of encapsulated enzymes and conferring magnetic properties to organic nanotubes and nanocoils. Simple recovery and separation with a magnet allow high reusability and recyclability of the bioreactors; in addition, nanotubes and nanocoils stabilize the encapsulated enzymes. The bioreactors work well even in the presence of proteases, which are able to eliminate the catalytic activity of enzymes in bulk solution.