2008 Volume 51 Issue 1 Pages 58-64
A series of bimetallic palladium-platinum (molar ratio Pd : Pt=4 : 1) catalysts supported on ytterbium (Yb)-modified ultrastable Y (USY) zeolite, Pd-Pt/Yb-USY, were prepared and characterized to investigate the effect of Yb loading (0-10.0 wt%) on the catalytic activity. Yb loading of less than 5.0 wt% enhanced the dispersion of Pd-Pt particles as well as the catalytic activity for hydrogenation (HYD) of tetralin and hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene. Improvement of HYD of tetralin was more significant than that of HDS after Yb loading. Interestingly, Yb loading decreased the inhibitory effect of tetralin on HYD of tetralin. Acidity measurements of Pd-Pt/Yb-USY catalysts showed that Yb modification selectively decreased the number of strong acidic sites and increased the number of medium and/or weak acidic sites with little change in the total amounts of acidity compared with the Pd-Pt/USY catalyst. Dispersion measurement by CO adsorption at 50°C showed that Yb loading promoted sulfidation of the surface of Pd-Pt particles, but TPR (temperature programmed reduction) measurements of sulfided Pd-Pt/Yb-USY catalyst showed that the affinity of Pd-Pt metallic phase to S weakened after Yb modification beyond the reduction temperature of 200°C. Therefore, Pd-Pt/Yb-USY catalyst has high potential for aromatic hydrogenation of industrial feedstocks containing large amounts of aromatic compounds, because this catalyst is highly sulfur-tolerant and more aromatic-tolerant than Pd-Pt/USY catalyst under hydrogenation reaction conditions.
