Enhancing the reactivity of gold: Nanostructured Au(111) adsorbs CO

Abstract

Low-coordinated sites are surface defects whose presence can transform a surface of inert or noble metal such as Au into an active catalyst. Starting with a well-ordered Au(111) surface we prepared by ion sputtering gold surfaces modified by pits, used microscopy (STM) for their structural characterization and CO spectroscopy (IRAS and NEXAFS) for probing reactivity of surface defects. In contrast to the Au(111) surface CO adsorbs readily on the pitted surfaces bonding to lowcoordinated sites identified as step atoms forming {111} and {100} microfacets. Pitted nanostructured surfaces can serve as interesting and easily prepared models of catalytic surfaces with defined defects that offer an attractive alternative to vicinal surfaces or nanoparticles commonly employed in catalysis science.

Elucidation of Active Sites for the Reaction of Ethanol on TiO2/Au(111)

“…The observation of two distinct desorption features in the TPD spectra indicates that there are two distinct adsorption sites for ethanol on Au(111). Previous studies of CO/Au(111) demonstrated that a sputtered Au(111) surface enhanced the adsorption of CO by exposing more undercoordinated Au step edges and kink sites. − CO had stronger binding energies to undercoordinated Au sites, which resulted in a higher T des . In order to investigate the desorption of ethanol from undercoordinated Au sites, the clean Au(111) surface was sputtered by bombarding the surface with 1 keV Ar + ions at 300 K. The morphology of a sputtered Au(111) single crystal was imaged using ex situ AFM, which showed the presence of large pits with roughened step edges (Figure S1).…”

Combining IR Spectroscopy and Monte Carlo Simulations to Identify CO Adsorption Sites on Bimetallic Alloys

“…The observation of only signals corresponding to CO adsorbed on top of gold atoms at the highest gold coverages, which follows the behavior seen previously by others, 39,40 is a good test for our model system. There is no clear indication in the literature for ordered CO structures on Au(111) surfaces and CO has been observed on Au(111) facets only at very low temperatures (much lower than those used in this study), or above 80 K on highcoordination number sites (steps, island borders, kinks and nanoparticle edges), or on terraces of Au thin films on another metal substrate which stabilizes adsorbed CO. 38,[40][41][42][43]48,49 Thus, it is not possible to make direct assignments of Au sites, and it can only be qualitatively shown that, as the Au coverage in the surface alloy decreases, the relative coverage of CO adsorbed on Au sites decreases. In addition, the Au infrared signals are broad (with a fwhm of ∼17−20 cm −1 ), suggesting no ordering, perhaps implying that CO agglomerates on the surface, possibly growing from step edges which have lowcoordinated Au atoms.…”

CO Adsorption on Au(332): Combined Infrared Spectroscopy and Density Functional Theory Study

“…An important tool to characterize the properties of adsorbed CO molecules is vibrational spectroscopy, which has been extensively used in the studies mentioned above. Unfortunately, the spectra reported did not reveal much information as they show a broad signal with some internal structure which could not be deconvoluted into contributions from different adsorption sites. ,, The problem arises from the fact that the stretching frequency of CO molecules depends on the coordination number of the metal atom, to which CO binds, but also on the coupling between the molecules, and hence on CO coverage. Different effects contribute to the shift due to coupling between molecules.…”