Surface Science 401 (1998) L371–L374 Surface Science Letters Nickeltetracarbonyl formation on non-equilibrium Ni surfaces V.K. Medvedev, R. Bo ¨rner, N. Kruse * Chemical Physics at Surfaces and Heterogeneous Catalysis, Free University of Brussels, Campus Plaine CP 243, 1050 Brussels, Belgium Received 24 November 1997; accepted for publication 2 January 1998 Abstract The subject of this investigation was the kinetics of Ni volatilization in form of nickeltetracarbonyl (Ni(CO) 4 ) during the interaction of CO gas with a Ni foil at room temperature (or slightly above). A trap-decomposition technique on an auxiliary Rh surface and posterior Auger spectroscopy were used for the product analysis. The presence of a high step site density (kinks) on an intentionally roughened Ni surface was found to cause a strong rate enhancement. CO pressures as low as 5×10-5 mbar turned out to be sufficient for the reaction to occur. However, a well-annealed equilibrium Ni surface remained inactive in Ni(CO) 4 formation under these conditions. A reaction model is presented by taking into account the present-day knowledge about Ni-subcarbonyl intermediate formation. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Auger electron spectroscopy; Carbon monoxide; Nickel; Nickelcarbonyl 1. Introduction suspicion turns true for non-equilibrium Ni sur- faces with high concentrations of step sites. Since the early days of surface science, the In applications of Ni-based heterogeneous catal- chemisorption of carbon monoxide on nickel sur- ysis Ni carbonylation is generally unwanted. faces has been amongst the most frequently studied Kinetic studies of the reaction [1–13] resulted in gas/solid systems. Much less attention was devoted rather divergent data. Depending on the sample to the dissolution process leading to the formation morphology, reaction rates were observed that of nickeltetracarbonyl, i.e. Ni (s) +4CO (g)  differed by several orders of magnitude. Quite Ni(CO) 4(g) . Indeed, the reaction is favoured by remarkably, steady-state carbonylation seems to high CO gas pressures and equilibrium thermo- be preceded by high initial rates [10,11]. dynamic data ( K p =7.2×103 bar -3 corresponding Mechanisms proposed for the deactivation are to DG0=−22.6 kJ mol -1) predict insignificant based on carbon formation [10]and morphological Ni(CO) 4 formation at low pressures, say changes [11] that lead to blocking and annihila- p CO <10-2 mbar. However, deviations of the Ni tion, respectively, of the active sites. surface topography from its equilibrium form may Kinetic studies of subcarbonyl formation, be suspected to alter the kinetics of this reaction. Ni(CO) x (ad) (x =1–3), demonstrated that synthesis The present Letter is intended to prove that this dominates over CO decomposition as long as the compression structure of chemisorbed CO is formed su fficiently fast [14]. These studies were * Corresponding author. Fax: ( +32 ) 2 650 5708; e-mail: nkruse@ulb.ac.be performed with Ni field emitter tips (containing 0039-6028/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0039-6028(98)00040-5