A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H-2) was investigated at 750 degrees C. Also, the catalysts were characterized by XRD, TEM, TPR and (in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH4 conversion of similar to 88%, CO selectivity of similar to 94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of CO3O4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl2O4 spinet phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al2O3 catalysts. (c) 2007 Elsevier B.V. All rights reserved.