Low-temperature CO adsorption on NiNaY leads to formation of Ni2+-CO Species (IR band at 2195 cm(-1)). In line with this, mainly mononitrosyls (1892 cm(-1)) are produced after NO adsorption on the sample. These results show the existence of one coordinative vacancy of the Ni2+ ions in NiNaY The results are compared with those of Ni-H-ZSM-5. In the latter case formation of dicarbonyls, dinitrosyls and mixed carbonyl-nitrosyl complexes of Ni2+ have been established. It was found that Ni-H-ZSM-5 is active in the selective catalytic reduction (SCR) of nitrogen oxides with methane, whereas the activity of NiNaY is rather poor. The stable species formed after coadsorption of NO and O-2 on both samples are surface nitrates and/or nitrites. However, whereas the monodentate nitrates on Ni-H-ZSM-5 are highly reactive towards methane, the reactivity of the nitrates/nitrites on NiNaY is significantly lower. The mechanism of SCR with methane is discussed. In particular, it is proposed that the high coordinative unsaturation of the Ni2+ cations in Ni-H-ZSM-5 is very important for the proceeding of SCR with methane. (C) 2004 Elsevier B.V. All rights reserved.