High chemical activity of a perovskite surface: reaction of CO with Sr$_3$Ru$_2$O$_7$

TL;DR

This study reveals that CO strongly reacts with Sr$_3$Ru$_2$O$_7$ surfaces, forming stable carboxylates and potentially explaining aging effects in perovskite oxides, using STM and DFT techniques.

Contribution

It provides new insights into CO adsorption and reaction mechanisms on Sr$_3$Ru$_2$O$_7$ surfaces, highlighting their high chemical activity and implications for surface stability.

Findings

CO binds strongly to Sr$_3$Ru$_2$O$_7$ surface sites.

Reaction of CO with surface forms stable Ru-COO species.

Reaction likely causes aging effects in perovskite oxides.

Abstract

Adsorption of CO at the Sr$_3$Ru$_2$O$_7$(001) surface was studied with low-temperature scanning tunneling microscopy (STM) and density functional theory. In situ cleaved single crystals terminate in an almost perfect SrO surface. At 78 K, CO first populates impurities and then adsorbs above the apical surface O with a binding energy E$_\mathrm{ads}$=-0.7 eV. Above 100 K, this physisorbed CO replaces the surface O, forming a bent CO2 with the C end bound to the Ru underneath. The resulting metal carboxylate (Ru-COO) can be desorbed by STM manipulation. A low activation (0.2 eV) and high binding (-2.2 eV) energy confirm a strong reaction between CO and regular surface sites of Sr$_3$Ru$_2$O$_7$; likely, this reaction causes the "UHV aging effect" reported for this and other perovskite oxides.