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

Abstract

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 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 CO 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.