Ligand Effect on the Stability of Water-Soluble Iridium Catalysts for High-Pressure Hydrogen Gas Production by Dehydrogenation of Formic Acid.

Aiming to develop a highly effective and durable catalyst for high-pressure H2 production from dehydrogenation of formic acid (DFA), the ligand effect on the catalytic activity and stability of Cp*Ir (Cp*:pentamethylcyclopentadienyl anion) complexes were investigated using 5 different kinds of N,N'-bidentate ligands (bipyridine, biimidazoline, pyridyl-imidazoline, pyridyl-pyrazole and picolinamide). The Ir complex with biimidazoline ligand exhibited the highest catalytic activity, but deactivation occurred readily at high pressure. The pyridine moiety in the ligand can enhance the stability of Ir complex catalysts for the high-pressure reaction. The Ir complex catalyst containing pyridyl-imidazoline ligand showed the high activity and best stability under the high-pressure conditions.