Selective oxidation of ammonia over Ru(0001) S.A.C. Carabineiro a , A.V. Matveev a,b , V.V. Gorodetskii a,b , B.E. Nieuwenhuys a, * a Leiden University, Leiden Institute of Chemistry, Surface Science and Heterogeneous Catalysis, Einsteinweg 55, 2333 CC Leiden, The Netherlands b Boreskov Institute of Catalysis, Russian Academy of Sciences, Novosibirsk 630090, Russia Received 28 November 2003; accepted for publication 6 February 2004 Abstract ThedecompositionandoxidationofNH 3 havebeenstudiedontheRu(0001)surfaceinthetemperaturerangefrom 150upto800K.TheresultswerecomparedtothosefoundforIr(110)andIr(510).TDSresultsshowedthatmostof the ammonia is dissociatively adsorbed between 150 and 300 K, with formation of H 2 around 300 K and N 2 between 600 and 800 K. N 2 desorption shifts to lower temperatures with increasing surface oxygen coverage. The products of ammonia oxidation observed were N 2 ,H 2 O and N 2 O. Formation of NO was not found. Inhibition of the reaction presumably by N specieswasobserveduntil450and670K,dependingontheNH 3 /O 2 ratios. Above those temperatures the reaction started as manifested by a decrease in the NH 3 and O 2 pressures and a simultaneous increase in the H 2 O, N 2 and N 2 O pressures. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Ammonia; Ruthenium; Oxygen; Nitrogen oxides; Nitrogen molecule; Catalysis; Chemisorption; Surface chemical reaction; Thermal desorption; Auger electron spectroscopy; Low energy electron diffraction (LEED) 1. Introduction The oxidation of ammonia can proceed via three main overall reactions [1–4]: 4NH 3 þ 5O 2 ! 4NO þ 6H 2 O ð1Þ 4NH 3 þ 3O 2 ! 2N 2 þ 6H 2 O ð2Þ 4NH 3 þ 4O 2 ! 2N 2 O þ 6H 2 O ð3Þ Reaction (1) is the so-called Ostwald process used to produce nitric acid. High temperatures (>800 K) are needed for this reaction. It has been studied intensively in the past because of its industrial importance. Relativelyfewstudieswerefocusedonreactions (2) and (3). However, the interest in reaction (2) is increasing due to its environmental aspect [5]. Reaction (3) might become a relevant reaction for N 2 O production. Recently it has been shown that this molecule may have a future as oxidant in selective catalytic oxidation [6–8]. Most of the fundamental studies concerning ammonia oxidation have been performed in con- nection with the production of NO on Pt and * Corresponding author. Tel.: +31-71-527-4545; fax: +31-71- 527-4451. E-mail address: b.nieuwe@chem.leidenuniv.nl (B.E. Nie- uwenhuys). 0039-6028/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2004.02.022 Surface Science 555 (2004) 83–93 www.elsevier.com/locate/susc