Efficient Pd on carbon catalyst for ammonium formate dehydrogenation: Effect of surface oxygen functional groups

Formate solution is a 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 HNO 3 solutions treatment or by H 2 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. • It is the first systematic investigation of the effects of the surface oxygen functional groups on formate dehydrogenation. • The Pd supported on reduced activated carbon pretreated with acid (Pd/re-ACA) has an exceptionally high TOF (13,511 h -1 ) than other Pd catalysts on oxidized carbon with nitric acid (Pd/ACA) under the identical reaction conditions. • Multiple characterizations, including in-situ ATR-IR, XPS, TEM, etc., and DFT simulations indicate that the roles of surface oxygen functional groups are complex: they lower the dehydrogenation reaction activation energies but impede the overall reaction rates.