Surface Science 433–435 (1999) 69–73 www.elsevier.nl/locate/susc Reactions between NO and CO on rhodium ( 111 ): an elementary step approach M.J.P. Hopstaken *, W.J.H. van Gennip, J.W. Niemantsverdriet Schuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands Abstract Reactions of adsorbed NO and CO on Rh(111) were studied with temperature programmed reaction spectrometry, using isotopically labeled 13CO to enable discrimination between N 2 and CO, and N 2 O and CO 2 . Dissociation and desorption of NO are hardly influenced by the presence of CO, whereas repulsion between NO and CO destabilizes CO, enhancing its desorption and diminishing the production of CO 2 . © 1999 Elsevier Science B.V. All rights reserved. Keywords: Automotive exhaust catalysis; Rhodium; Surface reactions 1. Introduction reaction at a range of coverages, which reveal several lateral interactions between CO and NO adsorbed on Rh(111). A key step in automotive exhaust catalysis, the reaction between CO and NO on the surface of rhodium, is of great practical and fundamental interest [1]. In principle, an adequate description 2. Experimental of the kinetics is available for the CO+NO reac- tion on Rh(111) when lateral interactions can be TPRS experiments were carried out in a UHV ignored, i.e. when the total surface coverage is stainless steel chamber (base pressure low. Attempts to include lateral interactions in 2×10-10 mbar) equipped with a Balzers Prisma mean field approaches have been made, by writing quadrupole mass spectrometer (QMA 200) and an the activation energy of surface reaction steps in Omicron LEED/Auger system [2]. The Rh(111) the form E a (h )=E a (0)(1-ah ), where h is the single crystal was cleaned as described before [3]. coverage and a is a pairwise interaction energy. Gases used were NO (99.5%, Messer Griesheim) Our aim is to eventually simulate the kinetics of and 13CO (99 at% 13C, Matheson). the CO+NO reaction by Monte Carlo methods, which o er the advantage that interactions and ordering phenomena can be accounted for in a 3. Results and discussion realistic way. Here we report temperature pro- grammed reaction measurements of the CO+NO Fig. 1 shows the temperature programmed reac- tion between 0.15 ML of CO and 0.24 ML of NO, representing a typical case of the reaction at low * Corresponding author. Fax: +31-40-2545-5054. E-mail address: tgtamh3@chem.tue.nl (M.J.P. Hopstaken) coverage where CO 2 , CO and N 2 are the only 0039-6028/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0039-6028(99)00063-1