Fine tuning the surface acid/base properties of single step flame-made Pt/alumina

Abstract

The acid/base properties of Pt/Al 2O 3 were modified by doping the support with SiO 2 or Cs 2O 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 0–100 wt.% SiO 2 or 0–10 wt.% Cs 2O. Up to 50 wt.% SiO 2 the BET surface areas could be kept in a narrow range (141 ± 15 m 2 g −1), while higher SiO 2 content increased the surface area and diminished the crystallinity of the support. CO chemisorption and XRD showed a positive correlation between the SiO 2 content and the size of the dominantly spherical Pt particles. The catalysts containing 22–30 wt.% SiO 2 were the most acidic as evidenced by TPD of NH 3. In the hydrogenation of acetophenone the SiO 2-doped catalysts were highly active and the selectivity to the hydrogenolysis byproducts increased with increasing SiO 2 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 Cs 2O barely affected the Pt particle size and TPD of CO 2 confirmed the increase of surface basicity with increasing Cs 2O content. Cs 2O was probably enriched at the Al 2O 3 surface and strongly influenced the acid/base properties and thus the catalytic performance already at very low concentrations. Only 0.25 wt.% Cs 2O blocked the hydrogenolysis of 1-phenylethanol to ethylbenzene.