Co-Al-BEA samples have been prepared in an attempt to introduce Co at tetrahedral lattice sites. No positive evidence of insertion has been gained, and no new Bronsted acidity is developed. The sample, instead, contains at least three families of Co2+ surface sites, CoA, CoB and CoC. CoA ions, the dominating species, are at extraframework positions (carbonyl species at 2208 cm(-1); mononitrosyl at 1939 cm(-1): a large fraction forms dinitrosyl species). CoB and CoC are two types of Co2+ ions grafted to the surface in defective situations (hydroxyl nests or stacking faults) and similar to Co species grafted to amorphous silica (carbonyl species at 2196 and 2184 cm(-1); mononitrosyl species at 1915 and 1895 cm(-1), respectively, form dinitrosyl species readily). Co3+ is also present in small amounts only after NO contact, and is responsible for a mononitrosylic species at 1954 cm(-1). Dinitrosyl species for CoA, CoB and CoC share the same modes at 1815 and 1900 cm(-1): Co3+(NO)(2) probably has the asymmetric mode at 1850 cm(-1). Interaction with ammonia of irreversibly adsorbed NO species suggests the possible occurrence of cation pairs. The availability of two coordinative unsaturations on most Co species (or the occurrence of cation pairs) allows a reversible disproportionation of NO2, consisting in the simultaneous adsorption of two molecules with a partial electron transfer from one ligand to the other, with formation of NO2delta+ and NO2delta- species: at a later stage of interaction, a proper disproportionation yielding nitrate species is observed. The presence of Co2+ ions at extraframework positions together with some dealumination of the samples accounts for the negligible presence of Bronsted acidity.