Formic acid dehydrogenation over PdNi alloys supported on N-doped carbon: synergistic effect of Pd–Ni alloying on hydrogen release

Abstract

Bimetallic Pd₁Ni_x alloys supported on nitrogen-doped carbon (Pd₁Ni_x/N–C, x = 0.37, 1.3 and 3.6) exhibit higher activities than Pd/N–C towards dehydrogenation of formic acid (HCO₂H, FA). Density functional theory (DFT) calculations provided electronic and atomic structures, energetics and reaction pathways on Pd(111) and Pd₁Ni_x(111) surfaces of different Pd/Ni compositions. A density of states (DOS) analysis disclosed the electronic interactions between Pd and Ni revealing novel active sites for FA dehydrogenation. Theoretical analysis of FA dehydrogenation on Pd₁Ni_x(111) (x = 0.33, 1 and 3) shows that the Pd₁Ni₁(111) surface provides optimum H₂-release efficiency via a favorable ‘HCOO pathway’, in which a hydrogen atom and one of the two oxygen atoms of FA interact directly with surface Ni atoms producing adsorbed CO₂ and H₂. The enhanced efficiency is also attributed to the blocking of an unfavorable ‘COOH pathway’ through which a C–O bond is broken and side products of CO and H₂O are generated.