Delving into the Chemical Deactivation of Palladium Catalysts during Spontaneous Formic Acid Dehydrogenation To Produce Dihydrogen

Spontaneous formic acid dehydrogenation (s-FAD) on a Pd-based catalyst produces H2 at room temperature with ∼100% selectivity, yet the accompanying chemical deactivation of the catalyst is not well understood, hampering the upgrading of the s-FAD system for practical applications. In this work, we demonstrate that the deactivation rate of s-FAD, as evaluated by online mass spectrometry, matches the surface CO accumulation rate, as measured by in situ attenuated total reflection–surface-enhanced infrared absorption spectroscopy, verifying that COads is the primary poisoning species during s-FAD on Pd catalysts. By quantifying the effects of solution pH, reactant concentration, kinetic isotope, and cation entity on COads formation rates, it is found that adsorbed formate is the precursor for COads while HCOOH serves as a Bro̷nsted acid. Furthermore, we clarify experimentally that the water-assisted CO2 hydrogenation pathway is responsible for the COads formation at Pd/solution interfaces during s-FAD. This work reveals that to maintain long-term high activity of s-FAD it is of great significance to graft a Bronsted base onto the Pd catalyst support as well as to optimize cation entities in solutions.