Investigation of CO Oxidation Transient Kinetics on an Oxygen Pre-covered Au(211) Stepped Surface Enrique Samano Æ Jooho Kim Æ Bruce E. Koel Received: 4 October 2008 / Accepted: 4 December 2008 / Published online: 23 December 2008 Ó Springer Science+Business Media, LLC 2008 Abstract The desire to explain the origin(s) of the unex- pected catalytic activity of oxide-supported Au nanoparticles for CO oxidation discovered by Haruta and coworkers has stimulated numerous experimental and theoretical studies of Au nanoclusters in the gas phase and on metal oxide supports, and on Au single-crystal surfaces. In order to explore further the reactivity of low-coordination Au step sites, we have performed transient kinetics studies of CO oxidation on an O-precovered, stepped Au(211) single crystal surface. We found behavior similar to that observed previously on flat Au(111) and (110) surfaces; i.e., there is no evidence in these transient kinetics for any special reactivity associated with this stepped Au surface. The CO oxidation reaction rate was highly dependent on the initial oxygen coverage, and we determined an apparent activation energy for CO oxidation of -7.0 kJ mol -1 for h O init = 0.9 ML. Within the Langmuir- Hinschelwood (LH) reaction scheme, we estimate an activa- tion energy of E LH = 20–43 kJ mol -1 on this surface for CO oxidation via this pathway. This is somewhat below the value of 67 kJ mol -1 predicted by recent theoretical calculations. Keywords Gold  Au(211)  Stepped surface  Chemisorption  Ozone  CO oxidation  Temperature programmed desorption (TPD) 1 Introduction While Au catalysts were known to be able to carry out a number of selective oxidation reactions, the discovery several years ago by Haruta and coworkers [1–3] of facile, low-temperature CO oxidation catalysis over supported Au nanoparticles rekindled an interest in Au catalysis and motivated an intense effort to investigate and explain the activity of these new catalysts. Numerous studies were initiated on Au single crystal surfaces and on Au clusters in the gas phase and deposited or grown on metal oxide supports. These studies have supported the early results in which, despite the fact that bulk Au is quite inert, nano- sized clusters of Au supported on metal oxides show cat- alytic activity for CO oxidation and also selective hydrocarbon oxidation [4]. Many explanations have been suggested to enlighten this remarkable activity of supported Au nanoclusters and the difficulty of explicitly probing and testing these explana- tions has hampered progress. One possibility that was suggested is that small nanoclusters can stabilize high concentrations of step sites or particular crystal planes (e.g., the Au(211) surface) that are highly active for such reactions [5–9]. To help evaluate this simple proposal, it is of interest to measure CO oxidation rates over bulk Au surfaces that present a high concentration of such reactive sites. While CO oxidation kinetics have been reported over Au(111) and Au(110)-(1 9 2) single crystal surfaces [10–13], no kinetics measurements of CO oxidation have been reported at step- ped Au surfaces or, in particular, on the Au(211) crystal plane. In this letter, we report on our investigations of CO oxidation kinetics on an Au(211) surface. Because of the low dissociation probability of O 2 on this surface [14], we performed transient kinetic measurements of CO titration of a preadsorbed oxygen adlayer on the Au(211) surface. E. Samano CNyN-Universidad Nacional Auto ´noma de Me ´xico, Apdo. Postal 356, 22860 Ensenada, Baja California, Mexico e-mail: samano@cnyn.unam.mx J. Kim  B. E. Koel (&) Department of Chemistry, Lehigh University, Bethlehem, PA 18015-3172, USA e-mail: brk205@lehigh.edu J. Kim e-mail: joohoky@yahoo.com 123 Catal Lett (2009) 128:263–267 DOI 10.1007/s10562-008-9815-8