The acid/base properties of Pt/Al2O3 were modified by doping the support with SiO2 or Cs2O and the catalysts were prepared by flame spray pyrolysis in a rapid, single step process with excellent reproducibility. The catalysts contained 4.7 wt.% Pt and the support composition varied in the range 0100 WtA SiO2 or 0-10 Wt-% Cs2O. Up to 50 Wt-% SiO2 the BET surface areas could be kept in a narrow range (141 +/- 15 m(2) g(-1)). while higher SiO2 content increased the surface area and diminished the crystallinity of the support. CO chemisorption and XRD showed a positive correlation between the SiO2 content and the size of the dominantly spherical Pt particles. The catalysts containing 22-30 wt.% SiO2 were the most acidic as evidenced by TPD of NH3. In the hydrogenation of acetophenone the SiO2-doped catalysts were highly active and the selectivity to the hydrogenolysis byproducts increased with increasing SiO2 content by more than 20-fold. This is a confirmation of the effect of support acidity on the properties of the Pt-H system. On the other hand, addition Of Cs2O barely affected the Pt particle size and TPD of CO2 confirmed the increase of surface basicity with increasing Cs2O content. Cs2O was probably enriched at the Al2O3 surface and strongly influenced the acid/base properties and thus the catalytic performance already at very low concentrations. Only 0.25 wt.% Cs2O blocked the hydrogenolysis of 1-phenylethanol to ethylbenzene. (c) 2009 Elsevier B.V. All rights reserved.