Carbon-supported Pt/C catalysts prepared with H2PtCl6 as metal precursor have been studied by temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and CO chemisorption in order to investigate the effect of acidity of the solution on the catalyst properties. The catalytic activity of the samples has been tested in structure insensitive reaction of cyclohexene hydrogenation. The catalysts were prepared by adsorption of platinum precursor on activated carbons with different pore structure followed by drying and reduction in flowing hydrogen at 523 K. The use of acidic and highly basic solution during the impregnation of microporous carbons led to highly dispersed catalysts with low activity. It has been suggested that a part of the supported metal became inaccessible to the organic substrate due to localization of metal particles in narrow pores of the support. However, in the range of intermediate solution pH, the activity per surface metal atom remained at a high level. Such phenomenon is attributed to the formation of bulky species of platinum precursor, which hardly penetrates into the small pores of the support, thus preventing a blocking effect. Effect of acidity of the solution proved significant for Pt/C catalysts on the activated carbons with the smaller micropores and higher concentration of oxygen-containing groups. (C) 2009 Elsevier B.V. All rights reserved.