Boosting the activity of PdAg alloy nanoparticles during H2 production from formic acid induced by CrOx as an inorganic interface modifier

Abstract

Interfacial modification of PdAg nanoparticles supported on mesoporous carbon (MSC) functionalized with weakly basic phenylamine groups was performed using an amorphous CrO_x phase. The resulting PdAgCr/amine-MSC catalyst was found to promote the efficient dehydrogenation of formic acid (HCOOH) serving as a liquid organic hydrogen carrier. A maximum turnover frequency of 6898 h⁻¹ (based on the mass of Pd employed) was achieved, which was 1.6 times larger than the value previously obtained using a PdAg catalyst. Physicochemical characterization and density functional theory calculations indicated that electronic interactions with the CrO_x phase induced a significant electronic gap. This effect, in turn, generated unique ensemble sites on the PdAg nanoparticle surfaces at which electron-deficient Ag^δ+ and electron-rich Pd^δ− atoms were adjacent. Kinetic analyses and theoretical investigations demonstrated that O–H bond dissociation was assisted by amine groups on the support surface. Enhanced C–H bond dissociation and H₂ desorption resulting from the cooperative action at the ensemble sites were found to play a crucial role in increasing the catalytic activity. The present system is easily synthesized, does not require additives, can be recycled and effectively suppresses CO formation, meaning that this material is a suitable candidate for practical applications in fuel cells.