Novel cobalt (Co), copper (Cu) and zinc (Zn) exchanged chabazite related SAPO-18 solid acid catalysts were prepared and characterised using techniques such as BET (nitrogen sorption), FrlR, ICP-OES, XPS and XRD. A detailed in situ FTIR investigation undertaken on the adsorption and disproportionation of NO and CO over Co-, Cu- and Zn-SAPO-18 molecular sieve catalysts indicated the formation of various NO/CO species or complexes with cationic Lewis acid and/or active metal sites. NO adsorption at room temperature leads to the formation of up to seven bands attributed to adsorbed nitrous oxide (N2O), chemisorbed nitrogen dioxide (NO2), nitrite (M-NO2) (M, metal), mononitrosyl (M-NO) and dinitrosyl [M-(NO)(2)] Complexes. CO adsorption at room temperature leads to the formation of up to six bands attributed to physi-sorbed carbon dioxide (CO2), cationic Lewis acid carbonyl moieties (L-CO) and transition metal carbonyl complexes (M-CO). The concentration and distribution of NO/CO species varies with pressure, reaction temperature and evacuation. (C) 2003 Elsevier Science B.V. All rights reserved.