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Tuning Strong MetalâSupport Interaction Kinetics on Pt-Loaded TiO<sub>2</sub>(110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study
Pt
catalyst particles on reducible oxide supports often change
their activity significantly at elevated temperatures due to the strong
metalâsupport interaction (SMSI), which induces the formation
of an encapsulation layer around the noble metal particles. However,
the impact of oxidizing and reducing treatments at elevated pressures
on this encapsulation layer remains controversial, partly due to the
âpressure gapâ between surface science studies and applied
catalysis. In the present work, we employ synchrotron-based near-ambient
pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect
of O2 and H2 on the SMSI-state of well-defined
Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr.
By tuning the O2 pressure, we can either selectively oxidize
the TiO2 support or both the support and the Pt particles.
Catalyzed by metallic Pt, the encapsulating oxide overlayer grows
rapidly in 1 Ă 10â5 Torr O2, but
orders of magnitude less effectively at higher O2 pressures,
where Pt is in an oxidic state. While the oxidation/reduction of Pt
particles is reversible, they remain embedded in the support once
encapsulation has occurred