Abstract
Clean and stable surface modifications of an iridium (100) single crystal, i.e., the (1 × 1) phase, the (5 × 1) reconstruction, and the oxygen-terminated (2 × 1)-O surface, were prepared and characterized by low energy electron diffraction (LEED), temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS) and polarization modulation IRAS (PM-IRAS). The adsorption of CO in UHV and at elevated (mbar) pressure/temperature was followed both ex situ and in situ on all three surface modifications, with a focus on mbar pressures of CO. The Ir(1 × 1) surface exhibited c(4 × 2)/c(2 × 2) and c(6 × 2) CO structures under low pressure conditions, and remained stable up to 100 mbar and 700 K. For the (2 × 1)-O reconstruction CO adsorption induced a structural change from (2 × 1)-O to (1 × 1), as confirmed by LEED, TPD, and IR. For Ir (2 × 1)-O TPD indicated that CO reacted with surface oxygen forming CO2. The (5 × 1) reconstruction featured a reversible and dynamic behavior upon CO adsorption, with a local lifting of the reconstruction to (1 × 1). After CO desorption, the (5 × 1) structure was restored. All three reconstructions exhibited CO adsorption with on-top geometry, as evidenced by IR. With increasing CO exposure the resonances shifted to higher wavenumber, due to adsorbate–adsorbate and adsorbate–substrate interactions. The largest wavenumber shift (from 2057 to 2100 cm–1) was observed for Ir(5 × 1) upon CO dosing from 1 L to 100 mbar.
Highlights
Previous studies have shown that the Ir(100) surface exhibits interesting properties with respect to its surface reconstructions
In the low pressure regime, the interaction with CO and the reactivity of different Ir surfaces has been examined by X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), ultraviolet photoelectron spectroscopy (UPS), high resolution electron energy loss spectroscopy (HREELS), and low energy electron diffraction (LEED).[8−12] it seems worthwhile to examine the interaction of the different Ir surface terminations with mbar pressures of CO as well
XPS spectra taken after the adsorption experiments confirmed the absence of CO dissociation, i.e., only molecular CO was present during the experiments
Summary
Previous studies have shown that the Ir(100) surface exhibits interesting properties with respect to its surface reconstructions. Since we intend to study the growth and catalytic properties[16] of epitaxially grown cobalt oxide model catalysts[15,17−19] (Co3O4 and CoO), detailed reference data (from UHV to elevated pressure) are required for the substrate, in order to confirm oxide film continuity, covering the entire substrate. In this respect, the properties of Received: December 21, 2015 Revised: April 21, 2016 Published: April 21, 2016. Following CO exposure, TPD revealed the formation of CO2 on the (2 × 1)O surface, whereas the other two reconstructions both exhibited CO desorption around ∼465 and 565 K
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