Substoichiometric ultrathin zirconia films cause strong metal-support interaction

P. Lackner, J. I. J. Choi, U. Diebold, M. Schmid

Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria

J. Mater. Chem. A 7 (2019) 24837-24846

The strong metal-support interaction (SMSI) leads to substantial changes of the properties of an oxide-supported catalyst after annealing under reducing conditions. The common explanation is the formation of heavily reduced, ultrathin oxide films covering metal particles. This is typically encountered for reducible oxides such as TiO2 or Fe3 O4. Zirconia (ZrO2) is a catalyst support that is difficult to reduce and therefore no obvious candidate for the SMSI effect. In this work, we use inverse model systems with Rh(111), Pt(111), and Ru(0001) as supports. Contrary to expectations, we show that SMSI is encountered for zirconia. Upon annealing in ultra-high vacuum, oxygen-deficient ultrathin zirconia films (~ZrO1.5) form on all three substrates. However, Zr remains in its preferred charge state of 4+, as electrons are transferred to the underlying metal. At high temperatures, the stability of the ultrathin zirconia films depends on whether alloying of Zr and the substrate metal occurs. The SMSI effect is reversible; the ultrathin suboxide films can be removed by annealing in oxygen.

Corresponding author: Michael Schmid (schmid at iap_tuwien_ac_at).

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