(782d) Unraveling the Nature of Boundary Sites of Metal-on-Oxide Catalysts
AIChE Annual Meeting
2016
2016 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Rational Catalyst Design III: Improving the Selectivity and Stability of Catalytic Sites
Friday, November 18, 2016 - 1:30pm to 1:50pm
The rise of density functional theory
(DFT) over the past few decades has enabled great progress in rational catalyst
design, especially for extended surfaces of transition metals [1]. However,
insights from such metal-only models do not always translate to real catalysts,
which usually consist of metal nanoparticles dispersed on high surface area
supporting phases. In this contribution, we examine how the inclusion of a
support phase can lead to deviations in reactivity compared to a metal-only
model. Specifically, we investigate the adsorption behavior of simple
adsorbates at the boundary of several late transition metals supported on MgO(100). We model the system as quasi one dimensional metal
nanowires on the oxide, similar to the model proposed by Molina et al [2], shown in Fig. 1. Our results show that the role
of the oxide is highly variable and strongly depends on the choice of metal and
adsorbate. For some metal-adsorbate combinations, the presence of the support
results in enhanced adsorption at the perimeter sites compared to the
unsupported metal nanowire. In other cases, adsorption is destabilized when the
metal is supported by the MgO. We have traced the origins of these
stabilization/destabilization effects to a combination of multiple structural
and electronic perturbations, including steric interactions, a shift in the
metal d-band center, and redox energy gained by charge transfer facilitated by
the oxide. Moreover, we show that in many cases, while the oxide has a
destabilizing effect on the adsorption of an atomic adsorbate, A, it has a stabilizing effect on the adsorption
of its hydrogenated form, AHx.
We use these results to discuss possible implications for scaling
relationships developed on metal-only models. [1] J. K. Norskov, Abild-Pedersen, F., Studt, F., &
Bligaard, T. (2011). PNAS, 108(3),
937-943.
(DFT) over the past few decades has enabled great progress in rational catalyst
design, especially for extended surfaces of transition metals [1]. However,
insights from such metal-only models do not always translate to real catalysts,
which usually consist of metal nanoparticles dispersed on high surface area
supporting phases. In this contribution, we examine how the inclusion of a
support phase can lead to deviations in reactivity compared to a metal-only
model. Specifically, we investigate the adsorption behavior of simple
adsorbates at the boundary of several late transition metals supported on MgO(100). We model the system as quasi one dimensional metal
nanowires on the oxide, similar to the model proposed by Molina et al [2], shown in Fig. 1. Our results show that the role
of the oxide is highly variable and strongly depends on the choice of metal and
adsorbate. For some metal-adsorbate combinations, the presence of the support
results in enhanced adsorption at the perimeter sites compared to the
unsupported metal nanowire. In other cases, adsorption is destabilized when the
metal is supported by the MgO. We have traced the origins of these
stabilization/destabilization effects to a combination of multiple structural
and electronic perturbations, including steric interactions, a shift in the
metal d-band center, and redox energy gained by charge transfer facilitated by
the oxide. Moreover, we show that in many cases, while the oxide has a
destabilizing effect on the adsorption of an atomic adsorbate, A, it has a stabilizing effect on the adsorption
of its hydrogenated form, AHx.
We use these results to discuss possible implications for scaling
relationships developed on metal-only models. [1] J. K. Norskov, Abild-Pedersen, F., Studt, F., &
Bligaard, T. (2011). PNAS, 108(3),
937-943.
[2] Molina, L.,
& Hammer, B. (2003). Phys. Rev.
Lett., 90(20), 206102.
Figure 1.
Structural model of a Pd nanowire supported on MgO(100).
An oxygen atom adsorbed at the metal-oxide boundary is also shown.
