NO adsorption and decomposition were studied on sulphided and sulphated copper-exchanged ZSM-5, AlMCM-41 and NbMCM-41 molecular sieves. FTIR, temperature-programmed reduction (H-2-TPR) techniques, adsorption, and catalytic measurements were applied. H2S adsorption drastically decreases the activity of copper-containing micro- and mesoporous materials studied in NO decomposition due to their sulphidation. This decrease is higher than that observed after SO2 treatment and is assigned to the formation of sulphide species. H2S is strongly chemisorbed on all copper active sites. Oxidation of sulphide species leading to the formation of sulphates does not increase the activity in the decomposition of NO, suggesting that some sulphided species are not oxidised. (C) 2000 Elsevier Science B.V. All rights reserved.