In the present work different adsorption modes of trichloroethene on the PdCu alloy have been investigated systematically. With application of ab initio periodic density functional theory, some insights about these adsorption modes have been revealed. The two different (110) terminations of the Cu3Pd alloy have been employed as models for the surface region of the Cu50Pd50 alloy because of Cu segregation. They are based on the regular phase of the face-centered cubic (fcc) structure. The first model shows a mixed (Pd/Cu =1) top layer, whereas the other one is Cu-terminated. The analysis of the position of the center of the d-band projected on the Pd and Cu atoms of both surfaces indicated that the Pd atom in the alloy has similar reactivity to the pure metal surface, whereas the opposite trend has been found for the Cu atoms. This has also been confirmed by the adsorption energy, calculated for the distinct modes. Trichlorethene prefers to interact with the Pd atoms on the mixed PdCu surface. Both di-sigma and pi modes are the most stable configurations among all studied. On the other hand, the adsorption via the chlorine atoms is the preferred on the Cu-terminated surface. The interaction of the C=C bond of trichloroethene on the Pd atoms is similar to the one of the ethene molecule. The main difference between the adsorption of these two molecules is due to the extra chlorine interactions with the Cu atoms. This allows one to suggest that the di-sigma configurations are the precursors of the dissociation reaction on the mixed surface.