The surface impurity of titanium with a low concentration on alumina was investigated to elucidate the effects of titanium to catalytic performance on Co/Ti-Al2O3 catalysts during Fischer-Tropsch (FT) synthesis. Titanium impurity is possibly incorporated as an impurity in Al2O3 preparation process, and its content could alter the surface characters of Al2O3. The variation of surface characteristics also significantly alters the dispersion of Co3O4 clusters, reducibility and it consequently changes the catalytic activity. In the present study, titanium impurity with a composition of 0.2-0.5 wt% on gamma-Al2O3 was found to be optimal to obtain a high catalytic performance with respect to CO conversion and C-5+ selectivity. The enhanced catalytic activity on Ti-modified Co/Al2O3 catalyst was mainly attributed to the increased dispersion of cobalt clusters homogeneously with a suppression of cluster aggregation during FT reaction, and it is mainly resulted from the surface modification of alumina with a low content of titanium oxides by changing the surface acidity of gamma-Al2O3. (C) 2012 Elsevier B.V. All rights reserved.