Hydrogenation of aromatics over Au-Pd/SiO2-Al2O3 catalysts: support acidity effect

Bimetallic Au-Pd catalysts supported on amorphous silica-alumina (ASA) with vary amount of alumina (0, 8, 14, 28 and 100%) were prepared by the simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polyvinylpyrrolidone (PVP). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicated formation of alloyed Au-Pd particles. Measurements of temperature-programmed desorption (TPD) of ammonia were performed to monitor the acid strength and the amount of acid sites on the catalysts after their reduction with 10% H2/Ar at 573K for 1 h. The effect of the support acidity on the catalytic activity was investigated in the simultaneous hydrogenation (HYD) of toluene (T) and naphthalene (NP) in the presence of dibenzothiophene (DBT). The amount of coke formed during the catalytic tests was also determined. Under the selected conditions (P = 5.0MPa, T = 523 K, WHSV = 41.2 h-1), all the catalysts were resistant to poisoning with 113 ppm of S (as DBT). The hydrogenation activity of toluene and the HDS activity of DBT correlate with the concentration of the medium strength acid sites. The enhancement of the HYD activity and the S-tolerance were related to modifications of the electronic properties of the metal atom upon interaction with the acid sites and upon intermetallic interaction.