A honeycomb catalyst for the oxidation or endogenous SO2 from a coal-fired power-station flue-gas has been developed. The catalyst reached a SO2 to SO3 conversion of 60 vol.% after 200 h in operation at the pilot plant. When this catalyst is further treated for another 100 h at lab scale to complete its activation, a stable 80 vol.% conversion is obtained. The results have been used to design an industrial unit for hue-gas conditioning to improve the fly ash collection by the electrostatic precipitator in a 220 MW coal-fired power plant. (C) 2000 Elsevier Science B.V. All rights reserved.