Palladium-doped silica–alumina catalysts obtained from double-flame FSP for chemoselective hydrogenation of the model aromatic ketone acetophenone

Chemoselective hydrogenation of aromatic ketones is an important reaction in the production of fine chemicals and pharmaceuticals. A typical example of this class of reactions is the hydrogenation of acetophenone (Aph) over the supported noble metal catalysts. In this research, Pd/silica–alumina (Pd/SA) catalysts have been prepared for Aph hydrogenation with the emerging double-flame spray pyrolysis system (decouples the two pathways of support formation and metal loading). The Pd particles offered identical electronic properties of Pd surface, which contributed the similar chemoselectivity for the hydrogenation of carbonyl groups on all double-flame-derived catalysts. This revealed a striking difference in Pd surface activity between double-flame and other 5%Pd/SA catalysts. While for supported-Pd catalysts synthesized by other methods, a significant ionic effect of support acidity on the surface Pd particles is reported, and this kind of surface electronic change was not observed for double-flame catalysts. The reaction rate of Aph hydrogenation could be strongly enhanced (TOF from 1.3 × 10−2 s−1 to 4.5 × 10−2 s−1) through tuning the density of surface Brønsted acid sites on supports of 5%Pd/SA via various Si/Al ratios. These advantages of double-flame-derived catalysts clearly demonstrate that double-flame spray pyrolysis can efficiently tune nano-catalysts and their bifunctional activities for specific surface reactions.