posted on 2020-03-19, 18:52authored byAlex C. Schilling, Kyle Groden, Juan Pablo Simonovis, Adrian Hunt, Ryan T. Hannagan, Volkan Çınar, Jean-Sabin McEwen, E. Charles H. Sykes, Iradwikanari Waluyo
The reducibility of metal oxides,
when they serve as the catalyst support or are the active sites themselves,
plays an important role in heterogeneous catalytic reactions. Here
we present an integrated experimental and theoretical study that reveals
how the addition of small amounts of atomically dispersed Pt at the
metal/oxide interface dramatically enhances the reducibility of a
Cu2O thin film by H2. X-ray photoelectron spectroscopy
(XPS) and temperature-programmed desorption (TPD) results reveal that,
upon oxidation, a PtCu single-atom alloy (SAA) surface is covered
by a thin Cu2O film and is, therefore, unable to dissociate
H2. Despite this, in situ studies using
ambient-pressure (AP) XPS reveal that the presence of a small amount
of Pt under the oxide layer can, at the single-atom limit, promote
the reduction of Cu2O by H2 at room temperature.
We built two density functional theory based surface models to better
understand these experimental findings: a Cu2O/Cu(111)-like
surface oxide layer, known as the “29” oxide, in which
Pt is alloyed into the Cu(111) surface, as well as a PtCu SAA. Our
calculations suggest that the increased activity is due to the presence
of atomically dispersed Pt under the surface oxide layer, which weakens
the Cu–O bonds in its immediate vicinity, thus making the interface
between subsurface Pt and the surface oxide a nucleation site for
the formation of metallic Cu. This initial step in the reduction process
results in the presence of surface Pt atoms surrounded by metallic
Cu patches, and the Pt atoms become active in H2 dissociation,
which consequently accelerates the reduction of the oxide layer. This
work demonstrates how isolated Pt atoms at the metal/oxide interface
of a Cu-based catalyst accelerate the reduction of the oxide and,
therefore, help maintain the active, reduced state of the catalyst
under the reaction conditions.