Efficient Pd on Carbon Catalyst for Ammonium Formate Dehydrogenation: Effect of Surface Oxygen Functional Groups

Abstract

Formate solution is one of a kind promising liquid organic hydrogen carrier but suffers from kinetic challenges. This study investigates the kinetics of the surface-functionalized Pd on carbon catalysts for formate dehydrogenation and the impact of O-functional groups. The fraction of the distinguished O-functional groups was modulated by the different concentrated HNO3 solutions treatment or by H2 reduction. This study shows that the O-functional groups play critical roles in dispersing Pd nanoparticles and decreasing the activation energy for dehydrogenation. Density functional theory (DFT) calculation reveals that most O-functional groups enhance formate adsorption on the Pd active site. However, the existence of C=O groups consumes reducing agents and hinders the formation of metallic Pd. The electron transfer from Pd to oxygen functional groups is unfavorable to dehydrogenation. The as-prepared Pd5/re-ACA (reduced activated carbon washed by acid) exhibited significant activity with a higher turnover frequency of 13,511 h-1 than commercial Pd/C.

Keywords: ammonium formate, O-functional group, dehydrogenation, LOHCs, palladium