Direct Observation of Hydroxyls Formed from Water and Oxygen on Ag(100)

TL;DR

Scientists observed hydroxyl groups forming on silver surfaces, which could impact how silver is used in chemical reactions.

Contribution

The study reveals the formation of hydroxyl groups on Ag(100) surfaces under vacuum, expanding understanding of silver's catalytic behavior.

Findings

Hydroxyl groups (OH) are present on Ag(100) surfaces at a binding energy of ∼531 eV.

The O/OH ratio is influenced by water exposure and surface temperature.

Formation of two OH groups from O and H2O is exothermic according to DFT calculations.

Abstract

The interaction of oxygen with silver is a key descriptor
of the
catalytic reactivity of silver nanoparticles which are ubiquitous
in large-scale partial oxidation reactions like ethylene epoxidation.
Despite Ag(100) being proposed as the most selective facet, it is
less studied than (111) and (110) surfaces. Using scanning tunneling
microscopy and synchrotron X-ray photoelectron spectroscopy, we report
that, in addition to the well-known O adatoms formed from O2 dissociation on Ag(100), hydroxyl groups (OH), at a binding energy
of ∼ 531 eV, are also present. The O/OH ratio depends on exposure
to water and surface temperature. These assignments are consistent
with our density functional theory calculations, which indicate that
the formation of two OH groups from an O atom and H2O molecule
is exothermic. These results indicate that, in addition to O, OH is
present even under ultrahigh vacuum conditions and therefore should
be considered in proposed catalytic pathways.

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