Unveiling the pressure dependent deactivation mechanism of iridium-based catalysts for hydrogen production from formic acid aqueous solutions

Iridium-based catalysts exhibit promising potential for large-scaled hydrogen production from formic acid due to their high activity and stability in base-free aqueous solutions. However, their reactivity and lifetimes are highly pressure dependent, diminishing substantially under pressurized conditions necessary for the suppression of foam formation, imposing grand challenges for both fundamental understanding and practical applications. In this work, the deactivation mechanism is elucidated. Through a combination of experimental analyses and density functional theory (DFT) calculations, ligand dissociation and hydrogen poisoning are identified as the major deactivation pathways. A kinetic model resulted from the mechanism suggests that the deactivation is also inversely correlated to the catalyst concentration, verified by experiments. Built upon these deactivation insights, a 10-fold increase in reaction rate and a 2.5-fold increase in catalyst lifetime under pressure have been successfully realized by the addition of ligand that suppresses both ligand dissociation and hydrogen poisoning. These results not only address difficulties in practical applications but also offer valuable insights for future catalyst design.