Role of Heteronuclear Interactions in Selective H-2 Formation from HCOOH Decomposition on Bimetallic Pd/M (M = Late Transition FCC Metal) Catalysts

Abstract

In this study, by using spin-polarized density functional theory calculations, we have elucidated the role of heteronuclear interactions in determining the selective H-2 formation from HCOOH decomposition on bimetallic Pd(shel)l/M-core (M = late transition FCC metal (Rh, Pt, Ir, Cu, Au, Ag)) catalysts. We found that the catalysis of HCOOH decomposition strongly depends on the variation of surface charge polarization (ligand effect) and lattice distance (strain effect), which are caused by the heteronuclear interactions between surface Pd and core M atoms. In particular, the contraction of surface Pd Pd bond distance and the increase in electron density in surface Pd atoms in comparison to the pure Pd case are responsible for the enhancement of the selectivity to H-2 formation via HCOOH decomposition. Our calculations also unraveled that the d band center location and the density of states for the d band (particularly d(z)(2), d(yz), and d(xz)) near the Fermi level are the important indicators that explain the impact of strain and ligand effects in catalysis, respectively. That is, the surface lattice contraction (expansion) leads to the downshift (upshift) of d band centers in comparison to the pure Pd case, while the electronic charge increase (decrease) in surface Pd atoms results in the depletion (augmentation) of the density of states for d(z2), d(yz), and d(xz) orbitals. Our study highlights the importance of properly tailoring the surface lattice distance (d band center) and surface charge polarization (the density of states for d(z2), d(yz), and d(xz) orbitals near the Fermi level) by tuning the heteronuclear interactions in bimetallic Pd-shell/M-core catalysts for enhancing the catalysis of HCOOH decomposition toward H-2 production, as well as other chemical reactions.