posted on 2021-07-21, 19:39authored byShahar Dery, Hillel Mehlman, Lillian Hale, Mazal Carmiel-Kostan, Reut Yemini, Tzipora Ben-Tzvi, Malachi Noked, F. Dean Toste, Elad Gross
Metal–support
interactions have been widely utilized for
optimizing the catalytic reactivity of oxide-supported Au nanoparticles.
Optimized reactivity was mainly detected with small (1–5 nm)
oxide-supported Au nanoparticles and correlated to highly reactive
sites at the oxide–metal interface. However, catalytically
active sites are not necessarily restricted to the interface but reside
as well on the Au surface. Uncovering the interconnection between
reactive sites located at the interface and those situated at the
metal surface is of crucial importance for understanding the reaction
mechanism on Au nanoparticles. Herein, high-spatial-resolution IR
nanospectroscopy measurements were conducted to map the localized
reactivity in hydrogenation reactions on oxide-supported Au particles
while using nitro-functionalized ligands as probes molecules. Comparative
analysis of the reactivity pattern on single particles supported on
various oxides revealed that oxide-dependent reactivity enhancement
was not limited to the oxide–metal interface but was detected
throughout the Au particle, leading to site-independent reactivity.
These results indicate that reactive Au sites on both the oxide–metal
interface and metal surface can activate the nitro groups toward hydrogenation
reactions. The observed influence of oxide support (TiO2 > SiO2 > Al2O3) on the overall
reactivity pattern specified that hydrogen dissociation occurred at
the oxide–metal interface, followed by highly efficient intraparticle
hydrogen atom diffusion to the interior parts of the Au particle.
In contrast to Au particles, the oxide–metal interface had
only a minor impact on the reactivity of supported Pt particles in
which hydrogen dissociation and nitro group reduction were effectively
activated on Pt sites. Single-particle measurements provided insights
into the relative reactivity pattern of oxide-supported Au particles,
revealing that the less-reactive Au metal sites can activate hydrogenation
reactions in the presence of hydrogen atoms that diffuse from the
Au/oxide boundary.