4 research outputs found
Rhodium–Tin Binary NanoparticleA Strategy to Develop an Alternative Electrocatalyst for Oxygen Reduction
A Rh–Sn nanoparticle
is achieved by combinatorial approaches
for application as an active and stable electrocatalyst in the oxygen
reduction reaction. Both metallic Rh and metallic Sn exhibit activities
too low to be utilized for electrocatalytic reduction of oxygen. However,
a clean and active Rh surface can be activated by incorporation of
Sn into a Rh nanoparticle through the combined effects of lateral
repulsion, bifunctional mechanism, and electronic modification. The
corrosion-resistant property of Rh contributes to the construction
of a stable catalyst that can be used under harsh fuel cell conditions.
Based on both theoretical and experimental research, Rh–Sn
nanoparticle designs with inexpensive materials can be a potential
alternative catalyst in terms of the economic feasibility of commercialization
and its facile and simple surfactant-free microwave-assisted synthesis
Role of Heteronuclear Interactions in Selective H<sub>2</sub> Formation from HCOOH Decomposition on Bimetallic Pd/M (M = Late Transition FCC Metal) Catalysts
In
this study, by using spin-polarized density functional theory
calculations, we have elucidated the role of heteronuclear interactions
in determining the selective H<sub>2</sub> formation from HCOOH decomposition
on bimetallic Pd<sub>shell</sub>/M<sub>core</sub> (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<sub>2</sub> 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<sub><i>z</i><sup>2</sup></sub>, d<sub><i>yz</i></sub>, and d<sub><i>xz</i></sub>) 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<sub><i>z</i><sup>2</sup></sub>,
d<sub><i>yz</i></sub>, and d<sub><i>xz</i></sub> 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<sub><i>z</i><sup>2</sup></sub>, d<sub><i>yz</i></sub>, and d<sub><i>xz</i></sub> orbitals near the Fermi level) by tuning the heteronuclear interactions
in bimetallic Pd<sub>shell</sub>/M<sub>core</sub> catalysts for enhancing
the catalysis of HCOOH decomposition toward H<sub>2</sub> production,
as well as other chemical reactions
Impact of d‑Band Occupancy and Lattice Contraction on Selective Hydrogen Production from Formic Acid in the Bimetallic Pd<sub>3</sub>M (M = Early Transition 3d Metals) Catalysts
Catalysts
that are highly selective and active for H<sub>2</sub> production
from HCOOH decomposition are indispensable to realize
HCOOH-based hydrogen storage and distribution. In this study, we identify
two effective routes to promoting the Pd catalyst for selective H<sub>2</sub> production from HCOOH by investigating the effects of early
transition metals (Sc, Ti, V, and Cr) incorporated into the Pd core
using density functional theory calculations. First, the asymmetric
modification of the Pd surface electronic structure (d<sub><i>z</i><sup>2</sup></sub> vs d<sub><i>yz</i></sub> +
d<sub><i>zx</i></sub>) can be an effective route to accelerating
the H<sub>2</sub> production rate. Significant charge transfer from
the subsurface Sc atom to the surface Pd atom and subsequent extremely
low level of d band occupancy (<0.1) around the Sc atoms are identified
as a key factor in deriving the asymmetric modification of the Pd
surface electronic structure. Second, in-plane lattice contraction
of the Pd surface can be an effective route to suppressing the CO
production. Compressive strain of the Pd surface is maximized as a
result of alloying with V and induces subsequent changes in adsorption
site preference of the key intermediates for the CO production path,
resulting in a significant increase in the activation energy barrier
for the CO production path. The unraveled atomic-scale factors underlying
the promotion of the Pd surface catalytic properties provide useful
insights into the efforts to overcome limitations of current catalyst
technologies in making the HCOOH-based H<sub>2</sub> storage and distribution
economically feasible
Importance of Ligand Effect in Selective Hydrogen Formation via Formic Acid Decomposition on the Bimetallic Pd/Ag Catalyst from First-Principles
The
critical role of the Ag–Pd ligand effect (which is tuned
by changing the number of Pd atomic layers) in determining the dehydrogenation
and dehydration of HCOOH on the bimetallic Pd/Ag catalysts was elucidated
by using the spin-polarized density functional theory (DFT) calculations.
Our calculations suggest that the selectivity to H<sub>2</sub> production
from HCOOH on the bimetallic Pd/Ag catalysts strongly depends on the
Pd atomic layer thickness at near surface. In particular, the thinnest
Pd monolayer in the Pd/Ag system is responsible for enhancing the
selectivity of HCOOH decomposition toward H<sub>2</sub> production
by reducing the surface binding strength of specific intermediates
such as HCOO and HCO. The dominant Ag–Pd ligand effect by the
substantial charge donation to the Pd surface from the subsurface
Ag [which significantly reduce the density of state (particularly, <i>d</i><sub><i>z</i><sup>2</sup></sub><sub>–<i>r</i><sup>2</sup></sub> orbital) near the Fermi level] proves
to be a key factor for the selective hydrogen production from HCOOH
decomposition, whereas the expansive (tensile) strain imposed by the
underlying Ag substrate plays a minor role. This work hints on the
importance of properly engineering the surface activity of the Ag–Pd
core–shell catalysts by the interplay between ligand and strain
effects