Effect of Pt dispersion on the catalytic performance of Pt/Al2O3 for CO and C3H6 oxidation was investigated. The intrinsic activity, expressed in terms of turnover frequency (TOF), for CO oxidation on Pt/Al2O3 catalysts was found to be almost identical irrespective of Pt dispersion. Pt dispersion is the most important factor to determine the CO oxidation activity. On the other hand, the TOF values for C3H6 oxidation on Pt/Al2O3 catalysts were found to increase with increasing the Pt dispersion to 0.20 and then remain almost invariable above D-Pt = 0.20. In situ FT-IR spectroscopy suggested that acrylate species participates as a reaction intermediate in C3H6 oxidation on Pt/Al2O3 and the formation and reaction behavior of the acrylate species is different depending on the Pt dispersion. The acrylate species formed on Pt/Al2O3 with higher Pt dispersion can readily react with oxygen to form CO2. On the other hand, the reaction of acrylate species is the slow step in the reaction over Pt/Al2O3 with D-Pt = 0.07. Low TOF values on Pt/Al2O3 with lower Pt dispersion were considered to be due to the inhibition of catalytically active site by accumulation of acrylate species. (c) 2013 Elsevier B.V. All rights reserved.