Hydrodesulfurization and hydrogenation of model compounds on silica–alumina supported bimetallic systems☆

Silica–alumina supported Pd catalysts with a second metal such as Cu, Ru or Pt have been prepared (nominal content: 1 wt%) and tested in the naphthalene hydrogenation (HYD) and dibenzothiophene hydrodesulfurization (HDS) model reactions. These catalysts were characterized by means of temperature-programmed reduction, NH3 temperature-programmed desorption and photoelectron spectroscopy techniques. The combined use of all these techniques revealed that only in the case of PtPd system a rather uniform distribution of the metals across the pore network is achieved. Another important observation was that the PtPd system exhibited strong Brönsted acid sites. The highest HYD and HDS activities of the PtPd bimetallic catalyst can be related not only to a high dispersion of the metals and their uniform distribution but also to its strong Brönsted acidity. The PtPd system presented the highest DBT conversion (83.1%) and the highest C–S hydrogenolysis activity as illustrated by the lowest S-containing products (21.9 wt%) as compared with the much higher S-containing products (54.8 wt%) obtained with the monometallic Pd/ASA catalyst under the same experimental conditions.