To obtain a broad understanding of the effect of preparation conditions on the platinum metal dispersion and the effect of dispersion on turnover frequencies (TF) of several representative reactions, we prepared platinum-supported alumina catalysts by impregnation methods in which preparation conditions were fixed or not fixed using certain alumina. Platinum dispersions on the alumina catalysts were determined by several methods. Catalytic activities for combustion of propane, oxidation of CO, hydrogenations of ethylene and naphthalene, hydrodechlorination of 1,1,1-trichloroethane, hydrodesulfurization of thiophene, and hydrocracking of hexane were compared based on the TF of these reactions. The following results were obtained: (i) high dispersion of platinum was achieved without extra modification for the catalyst preparation method; (ii) an attentive pretreatment brought high reproducible results in platinum dispersions; (iii) the catalytic activities for combustion of propane, hydrodesulfurization of thiophene and hydrogenation of naphthalene were affected by starting materials of platinum; (iv) the relation between the TF and platinum dispersion was negative in all reactions tested except hydrocracking of hexane. (C) 2004 Elsevier B.V. All rights reserved.