Effects of CeO2 addition on the catalytic performance of Ni/Al2O3 catalysts for ammonia decomposition to hydrogen were investigated by activity studies and some physico-chemical methods like N-2-adsorption/-desorption, H-2-Chemisorption, X-ray diffraction (XRD), H-2 temperature-programmed reduction (H-2-TPR) and NH3 temperature-programmed surface reduction (NH3-TPSR). The results showed that the addition of CeO2 greatly improved the catalytic activity and stability of Ni/Al2O3 catalysts for ammonia decomposition to COx-free hydrogen. 98.3% NH3 conversion and 32.9 mmol/(min g(cat)) H-2 formation rate were achieved over CeO2 promoted Ni/Al2O3 catalyst at 823 K and 30 000 ml/(h g(cat)) NH3 space velocity. The characterization results indicate that the addition of CeO2 enlarged the catalyst pores, moderated the interaction between Ni and alumnia, suppressed Ni-0 crystallites from sintering, and improved the recombinative desorption of N adatoms from the Ni-0 surface. (C) 2007 Elsevier B.V. All rights reserved.