Activated carbons impregnated with CoO, Co3O4 and CrO3 were prepared, to be used in the oxidative destruction of atmospheric organic pollutants. To analyse the influence of impregnation methodology on the structure, the impregnation step was conducted after activation and after carbonization. When impregnation is made after activation, the impregnated salts must be deposited on the internal surface, blocking the access to part of the initial structure. When impregnation is made after carbonization, the impregnated active carbons have even more important contribution of micro and mesoporosity. The metallic impregnants catalyse the activation step, allowing a controlled development of the larger micropores and mesopores, i.e. bigger for higher metal percentages and with Co3O4 as catalyst.