2 research outputs found
Controlling Catalytic Selectivity on Metal Nanoparticles by Direct Photoexcitation of AdsorbateāMetal Bonds
Engineering heterogeneous metal catalysts
for high selectivity
in thermal driven reactions typically involves the synthesis of nanostructures
with well-controlled geometries and compositions. However, inherent
relationships between the energetics of elementary steps limit the
control of catalytic selectivity through these approaches. Photon
excitation of metal catalysts can induce chemical reactivity channels
that cannot be accessed using thermal energy, although the potential
for targeted activation of adsorbateāmetal bonds is limited
because the processes of photon absorption and adsorbateāmetal
bond photoexcitation are typically separated spatially. Here, we show
that the use of sub-5-nanometer metal particles as photocatalysts
enables direct photoexcitation of hybridized adsorbateāmetal
states as the dominant mechanism driving photochemistry. Activation
of targeted adsorbateāmetal bonds through direct photoexcitation
of hybridized electronic states enabled selectivity control in preferential
CO oxidation in H<sub>2</sub> rich streams. This mechanism opens new
avenues to drive selective catalytic reactions that cannot be achieved
using thermal energy
Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with <i>in Situ</i> TEM and IR
Atomic-scale
insights into how supported metal nanoparticles catalyze
chemical reactions are critical for the optimization of chemical conversion
processes. It is well-known that different geometric configurations
of surface atoms on supported metal nanoparticles have different catalytic
reactivity and that the adsorption of reactive species can cause reconstruction
of metal surfaces. Thus, characterizing metallic surface structures
under reaction conditions at atomic scale is critical for understanding
reactivity. Elucidation of such insights on high surface area oxide
supported metal nanoparticles has been limited by less than atomic
resolution typically achieved by environmental transmission electron
microscopy (TEM) when operated under realistic conditions and a lack
of correlated experimental measurements providing quantitative information
about the distribution of exposed surface atoms under relevant reaction
conditions. We overcome these limitations by correlating density functional
theory predictions of adsorbate-induced surface reconstruction visually
with atom-resolved imaging by <i>in situ</i> TEM and quantitatively
with sample-averaged measurements of surface atom configurations by <i>in situ</i> infrared spectroscopy all at identical saturation
adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle
surface reconstruction induced by CO adsorption at saturation coverage
and elevated (>400 K) temperature, which is relevant for the CO
oxidation
reaction under cold-start conditions in the catalytic convertor. Through
our correlated approach, it is observed that the truncated octahedron
shape adopted by bare Pt nanoparticles undergoes a reversible, facet
selective reconstruction due to saturation CO coverage, where {100}
facets roughen into vicinal stepped high Miller index facets, while
{111} facets remain intact