Hydrogenation of diethylbenzenes in the liquid phase was studied at 358-418 K and 2-6 MPa over 16.7% Ni/Al2O3. The reactivity of diethylbenzene isomers was dependent on the mutual position of the substituents and decreased in the following order: 1,3- > 1,4- > 1,2-. The apparent activation energies were ca. 60 kJ/mol. The cis-to-trans ratio of the corresponding saturated products exhibited only a weak dependence on temperature and hydrogen pressure. (c) 2004 Elsevier B.V. All rights reserved.