CO and H 2 O adsorption and reaction on Au(310) M.E. van Reijzen, M.A. van Spronsen, J.C. Docter, L.B.F. Juurlink ⁎ Leiden Institute of Chemistry, Leiden University, PO BOX 9502, 2300 RA, Leiden, The Netherlands abstract article info Article history: Received 7 April 2011 Accepted 3 June 2011 Available online 15 June 2011 Keywords: Gold Carbon monoxide Water Surface chemical reaction Stepped single crystal surface We have studied desorption of 13 CO and H 2 O and desorption and reaction of coadsorbed, 13 CO and H 2 O on Au(310). From the clean surface, CO desorbs mainly in, two peaks centered near 140 and 200 K. A complete analysis of desorption spectra, yields average binding energies of 21 ± 2 and 37 ± 4 kJ/mol, respectively. Additional desorption states are observed near 95 K and 110 K. Post-adsorption of H 2 O displaces part of CO pre-adsorbed at step sites, but does not lead to CO oxidation or significant shifts in binding energies. However, in combination with electron irradiation, 13 CO 2 is formed during H 2 O desorption. Results suggest that electron- induced decomposition products of H 2 O are sheltered by hydration from direct reaction with CO. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Catalytic activity of gold has been a topic of research since the 1960s [1]. However, it has only attracted significant attention since Haruta's discovery of Au nanoparticles' high activity for CO oxidation [2]. Since this pioneering work, Au nanoparticles have been found to catalyze many more reactions [3–6]. In parallel, surface science studies have investigated the reaction mechanisms underlying gold's remarkable reactivity using well-ordered Au single crystal surfaces. These studies have been reviewed recently [7–10]. The origin of the high catalytic activity of Au nanoparticles toward CO oxidation, and in particular the promotional effect of H 2 O on the oxidation rate, are still under debate [11–13]. Based upon catalytic studies of supported Au particles, Daté and Haruta suggested direct reaction of H 2 O with O 2 yielding OH groups and an activated O atom at the perimeter of nanoparticles as a possible means for H 2 O to increase reactivity [11]. Another suggested mechanism was the facilitation of carbonate (CO 3 ) dissociation by water, again accompanied by formation of hydroxyl groups. Recent combinations of density functional theory (DFT) studies and molecular beam experiments [12], near-edge X-ray absorption fine structure (NEXAFS) and infra- red (IR) studies [13], and temperature programmed desorption (TPD) and IR studies [14] using a Au(111) single crystal surface show unambiguously that H 2 O and surface-bound atomic O form OH groups. These OH groups readily oxidize CO at a surface temperature of 77 K using a CO molecular beam [12]. The reaction is suggested to proceed via an unstable HO–CO intermediate [13]. Although hydroxyl formation from O + H 2 O is observed on many other transition metals [15–17] and may be expected to be part of the explanation of gold's capability to oxidize CO at low temperatures, it is not obvious that its occurrence on Au(111) reflects what happens on real catalyst particles. First, such particles are only active in CO oxidation when smaller than 5 nm [3] and at such diameters large (111) domains are not abundant at the catalyst's surface. Second, small particles contain many low coordinated sites, for example at the border between two facets, where the formation of OH from O + H 2 O may not occur to a large extent. For two stepped Pt surfaces, we have recently shown that the (111) terraces, (110) steps and (100) steps have strongly varying tendencies to producing OH from coadsorption of O+H 2 O [18]. In this article, we investigate the influence of low coordinated Au atoms on coadsorbed CO and H 2 O. We use the Au(310) surface, which consists of 3-atom wide (100) terraces with monoatomic (110) steps. The surface therefore provides 6-, 8- and 9-fold coordinated atoms, as indicated in Fig. 1a, to interact with adsorbates. We use TPD, Auger electron spectroscopy (AES), and low energy electron diffraction (LEED) in our investigations of adsorption and desorption. 2. Experimental Experiments are carried out using a home-built ultrahigh vacuum (UHV) system with a base pressure of 1×10 -10 mbar during experi- ments. The UHV chamber and manipulator are constructed for studies of single crystal samples. The chamber is equipped with two quadrupole mass spectrometers (QMS). One QMS (Baltzers, Prisma 200) protrudes into the main chamber and is used for residual gas analysis and angle- integrating TPD spectroscopy. The other QMS (UTI 100c) is differentially pumped and probes desorption of molecules from the sample through a 3 mm diameter opening, positioned ~2 mm away from the face of the Surface Science 605 (2011) 1726–1731 ⁎ Corresponding author. Tel.: + 31 71 527 4221; fax: + 31 84 7182999. E-mail address: l.juurlink@chem.leidenuniv.nl (L.B.F. Juurlink). 0039-6028/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2011.06.006 Contents lists available at ScienceDirect Surface Science journal homepage: www.elsevier.com/ locate/susc