Ion-exchanged Co and PdCo-BEA zeolite-based catalysts were studied for the selective catalytic reduction (SCR) of NO with methane under oxygen excess. Bimetallic samples were submitted to several hydrothermal treatments (steaming) and tested under dry and wet conditions (2% H2O). These hydrothermal treatments resulted in significant modifications in the amount and distribution of metal species, namely an increase of Co oxides and Co-oxo species, simultaneously with the preservation of Co2+ isolated exchanged cations. H-2-TPR measurements detected, on these catalysts, a fraction of Co species more easily reducible, eventually interacting with Pd species and possibly related to dispersed nanosized oxide species, placed in more accessible positions. All the steamed catalysts exhibit a higher NO conversion into N-2 and an increased water resistance. The Co and/or Co-Pd species formed during steaming treatment, the balance between them and the framework dealumination are important issues for the high and stable catalyst activity under the presence of water vapor. (c) 2005 Elsevier B.V. All rights reserved.