The deactivation mechanism and regeneration of spent industrial Pt-NiO/Al2O3 catalysts used for NO(x) reduction was studied by means of SEM-EDS, chemical analysis and kinetic measurements. It was found that the main cause of deactivation under industrial operating conditions is fouling due to carbonaceous and ZnO deposits. Various contaminant removal procedures (calcination, wet screening and acetic acid leaching) were tested and the influence of these procedures on contaminant removal and the catalyst activity were investigated. Regeneration of the spent industrial catalyst using inexpensive processes was shown to be feasible.