The hydrogenation of maleic anhydride to succinic anhydride was carried out over Ni/Al2O3-HY catalysts. The catalysts, which contained 3-30 wt % Ni, were prepared via a kneading method. The catalysts were characterized by an array of techniques, including X-ray diffraction (XRD) and H-2 temperature-programmed reduction (TPR). The nature of the Ni species on the support, and their interaction with the support, were studied. XRD and TPR studies showed that nickel was present as Ni2+ and Ni3+ species on the support, and that there was no elemental nickel (Ni-0) in the unreduced samples. Pretreatment using pure H-2 at different temperatures affected the reactivity. Pretreatment at 350 degrees C for 3 h was the best among the conditions tested.