Nickel spinels were synthesized in order to be used as supports of nickel catalysts for the hydrodechlorination of 1,2,4-trichlorobenzene in the gas phase. All the samples were structurally characterized using X-ray diffraction (XRD), BET, temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and temperature-programmed desorption (TPD) techniques. The Ni/NiAl2O4 catalysts tested had high conversions and selectivities towards benzene. This is due to their reduction degree (XRD) and structural surface properties (BET area, SEM, TPD). The most active and selective catalyst yields 87% benzene at 523 K for a conversion of 82%. These Ni/spinel catalysts desorb large amounts of hydrogen at lower temperatures (<625 K) which can compete with the aromatic compounds to be adsorbed on the surface of the catalyst. The amount of low-temperature hydrogen and the fact that it competes with the aromatic molecules favour a more exhaustive hydrodechlorination. (C) 2000 Elsevier Science B.V. All rights reserved.