Thermal behaviour of hydrous ruthenia (RuO2.nH(2)O) and ruthenia containing 10% titania ((RuO2)(0.9)-(TiO2)(0.1).nH(2)O) was characterised on heating in air by emanation thermal analysis (ETA), thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA). The anhydrous ruthenia and ruthenia containing 10% titania samples were prepared by heating their hydrous precursors at 500degreesC in air. The temperature intervals of the samples dehydration and crystallisation were determined. XRD, TEM and surface area measurements were also used for the characterisation of the samples. The ETA results, evaluated by a mathematical model, brought about new information about surface area and microstructure development of the intermediate products of the oxides under in situ conditions of the heating in air. A good agreement between ETA and the results of other methods was obtained. The NOx reduction by CO was used to test the catalytic properties of these samples. (C) 2004 Kluwer Academic Publishers.