PCDD/F formation on fly ashes, the effect of inhibitors was studied by this technique. While no inhibitory action was observed for triethylamine, ethanolamine was shown to act as a very efficient inhibitor, by blocking the active sites of copper surfaces. At this point it is important to draw attention to the differences between the carefully prepared surfaces investigated in this study, and the highly heterogeneous fly ash in the complex environment of an incinerator. Details of the phenomena observed in the laboratory cannot be transferred to the technical plant, and we cannot exclude the possiblity that other modes of inhibitory action are important in the incinerator environment. However, the relevant results on the inhibition of dioxin formation obtained in the pilot plant are consistent with the mechanisms proposed in this study.