The chemisorption and reaction of trans-dichloroethene on Cu(110) have been investigated by high-resolution electron-energy-loss spectroscopy (HREELS) as a function of coverage and temperature. At 135 K, both physisorbed and chemisorbed trans-dichloroethene are present. Heating to 200 K leads to the formation of acetylene and of a partially dehalogenated intermediate species. By 300 K, the acetylene trimerises to form adsorbed benzene at the surface. Adsorption of trans-dichloroethene at 300 K produces benzene directly. Evidence of C-Cl cleavage at temperature as low as 220 K is clearly marked by the emergence of very intense Cu-Cl stretching vibrations which remain even after further heating up to 570 K.