The use of bio-fuels is becoming more important because of the environmental benefits associated with these fuels. Deactivation of SCR catalysts applied in bio-fuel plants is a major problem due to the high potassium content of bio-fuels and therefore, great potential lies in finding regeneration processes that can be used commercially. Exposing the catalyst surface to sulphate groups generated by SO2 or H2SO4 is a promising way to rejuvenate the initial activity of the catalyst. The chemical stability of the sulphate groups was investigated by the interaction of the SCR reactant gases with the sulphate-promoted catalysts. Sulphate ions deposited on the surface of the TiO2/V2O5/WO3 were thermally stable at 420 degreesC. The introduced sulphate groups were chemically unstable when the catalyst was treated with the SCR reactants at 400 degreesC, but were chemically stable when the catalyst was exposed for the SCR reactants at 350 degreesC. Sulphation after water treatment provided more chemically stable surface sulphate groups at 400 degreesC. The presence of sulphate groups enhanced the number and the strength of the surface acid sites. The amount of ammonia bound to the Bronsted acid sites decreased with the potassium content of the catalyst while the amount of ammonia adsorbed on the Lewis acid sites was almost unaffected. Since potassium both retarded the redox potential of the surface vanadia species and decreased the amount of ammonia bound to the Bronsted acid sites, it is important to wash the strongly deactivated catalyst before sulphation.