Mixed oxides catalysts usable in particular in the full oxidation to CO2 and H2O of volatile organic compounds (VOC), in the decomposition of nitrogen protoxide to nitrogen and oxygen and the combustion of CO, H2 and CH4 off gases in fuel cells, comprising oxides of manganese, copper and La2O3 and/or Nd2O3, having a percentage composition by weight expressed as MnO, CuO, La2O3 and/or Nd2O3 respectively of 35-56%, 19-31% and 20-37%. The oxides are supported on inert porous inorganic oxides, preferably alumina.