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

Abstract

Bimetallic Pd1Nix alloys supported on nitrogen-doped carbon (Pd1Nix/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 Pd1Nix(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 Pd1Nix(111) (x = 0.33, 1 and 3) shows that the Pd1Ni1(111) surface provides optimum H-2-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 H-2. 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.