Abstract
The catalytic activities and properties of noble metals (Pt, Pd, Rh, Ru) supported on silica gel (SiO2) and alumina-modified silica gel (Al2O3-SiO2) were investigated for the hydrodesulfurization of thiophene. Al2O3-SiO2 was prepared by an impregnation method using aluminum nitrate (Al(NO3)3·9H2O) aqueous solution. Pt/8 wt%Al2O3-SiO2 catalyst showed the highest activity for hydrodesulfurization of thiophene among various supported noble metal catalysts and this activity was higher than that of commercial CoMo/Al2O3 hydrodesulfurization catalyst. The sulfur tolerance of noble metal/SiO2 was enhanced by Al2O3 modification of SiO2 and Pt/8 wt%Al2O3-SiO2 catalyst showed the highest sulfur tolerance among the supported noble metal catalysts. Pt/8 wt%Al2O3-SiO2 catalyst had high hydrogenating ability for unsaturated C4 hydrocarbons formed in the hydrodesulfurization of thiophene. The catalysts were characterized by 2-propanol dehydration, cumene cracking, XRD, H2 adsorption and FT-IR. Dispersion of Pt on 8 wt%Al2O3-SiO2 was remarkably higher than that on SiO2 and the particle size of Pt on 8 wt%Al2O3-SiO2 was the lowest among the supported noble metal catalysts. The acidity of 8 wt%Al2O3-SiO2 was higher than that of SiO2. Furthermore, Brönsted acid sites were present on 8 wt%Al2O3-SiO2. FT-IR spectroscopy of thiophene adsorbed on 8 wt%Al2O3-SiO2 support indicated that the thiophene molecule interacts with the Brönsted acid site on 8 wt%Al2O3-SiO2. The activity of the double-layer (Pt/SiO2 + 8 wt%Al2O3-SiO2) catalyst obtained experimentally was higher than that calculated. This suggests that spillover hydrogen was present on Pt/Al2O3-SiO2 in the hydrodesulfurization of thiophene. Both the Brönsted acid sites of Al2O3-SiO2 and the Pt particles in the Pt/Al2O3-SiO2 catalyst act as active sites for the hydrodesulfurization of thiophene.
