Several NiO-MgO systems were synthesized to be studied as nickel catalysts for the hydrogenation of 1,4-butanedinitrile in the gas phase and compared with a bulk NiO of controlled morphology, All samples were characterized by XRD, BET, TPR, TPD, SEM, and H-2 chemisorption techniques. The Ni-MgO systems had higher activities than the Ni bulk catalyst. The most active catalyst at all reaction temperatures was type R4C(B) which had homogeneous particles of about 1000 Angstrom, the highest metal surface area, and the highest coverage with weakly bound hydrogen. The presence of basic magnesia suppresses the condensation reactions and consequently favors the elimination of amines, and prevents catalyst deactivation. The selectivity toward the different products not only depends on the catalytic properties but can also be modified by controlling the hydrogen/dinitrile ratio. The highest selectivity to 4-aminobutanenitrile was achieved by catalyst R4C(B), with 85% at 100% conversion and working at a space velocity of 13,000 h(-1) and 343 K. This selectivity could be increased by lowering the hydrogen/butanedinitrile ratio. (C) 2001 Academic Press.