Post-synthesis alumination of MCM-41: Effect of the acidity on the HDS activity of supported Pd catalysts

Siliceous MCM-41 with different amount of alumina, from 0.25 up to 4.0 wt%, were prepared by impregnation of the MCM-41 with aqueous solution of Al(NO)3·9H2O. The modified mesoporous silicas were then used as supports for Pd catalysts prepared by wet-impregnation from PdCl2 precursor. Supports and corresponding Pd catalysts were characterized by XRD, XPS and NH3-TPD. The catalytic behavior was tested in the hydrodesulfurization (HDS) reaction of thiophene. An increase of the hydrodesulfurization activity with increasing alumina amount up to 0.5 wt% was observed. On the basis of the acidity change of the support and the structural modification underwent by the deposited palladium, the improved catalytic behavior was associated to the increased acidity of the supports and also to its effect on the palladium dispersion. A bi-functional mechanism, implying that metallic palladium activates the hydrogen and the thiophene molecules are adsorbed on the acid sites of the support, could be operative. However, the increased acidity was also responsible for the larger catalyst deactivation which limited the beneficial effect up to a certain amount of alumina content.

Figure optionsDownload high-quality image (73 K)Download as PowerPoint slideResearch highlights▶ Post-alumination of siliceous MCM-41 promotes thiophene HDS activity of supported Pd. ▶ The addition of Al 3+ to MCM-41 increases the acidity of the Pd catalysts. ▶ Bi-functional mechanism for the activation of thiophene over Pd catalysts. ▶ Direct correlation between catalyst deactivation and catalyst acidity.