In a method of preparing a ruthenium-containing catalyst on a non-conductive metal oxide support comprises dissolving one or more ruthenium precursor compounds in an liquid organic polyol, combining the thus obtained solution with (a) nano-powder(s) of one or more metal oxides in a ratio of moles metal oxide(s) to moles ruthenium atoms in the one or more ruthenium precursor compounds of about 0:1 to about 6:1, the metal oxide nano-powder(s) having a surface area of from about 5 to about 300 m 2 /g and a point of zero charge (PZC) of pH 5.5 or higher, agitating the thus obtained mixture, adding pre-shaped alumina support pellets to the agitated mixture, which is than heated at a temperature of about 50 °C to the boiling point of the organic polyol, until the reaction is finished, cooling the mixture and combining it with an aqueous solution of NaNO 3 and/or KNO 3 , agitating the resultant mixture, separating the solvent and the solids, and drying the thus obtained solid pellets of alumina, or alumina and the metal oxide(s) of the nano-powder(s) coated with ruthenium and an additional amount Na and/or K ions. Also disclosed is the supported ruthenium-containing catalyst obtainable by the method and the use thereof in decomposing ammonia into nitrogen and oxygen.