Effect of Yb Loading on Aromatic Hydrogenation Activity of Pd-Pt/USY Zeolite Catalysts

Abstract

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 investigatethe 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-Ptparticles 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 ofHDS after Yb loading. Interestingly, Yb loading decreased the inhibitoryeffect of tetralin on HYD of tetralin. Acidity measurements of Pd-Pt/Yb-USYcatalysts showed that Yb modification selectively decreased the numberof strong acidic sites and increased the number of medium and/orweak acidic sites with little change in the total amounts of aciditycompared with the Pd-Pt/USY catalyst. Dispersion measurement by COadsorption at 50 degrees C showed that Yb loading promoted sulfidationof the surface of Pd-Pt particles, but TPR (temperature programmedreduction) measurements of sulfided Pd-Pt/Yb-USY catalyst showedthat the affinity of Pd-Pt metallic phase to S weakened after Ybmodification beyond the reduction temperature of 200 degrees C. Therefore,Pd-Pt/Yb-USY catalyst has high potential for aromatic hydrogenationof industrial feedstocks containing large amounts of aromatic compounds,because this catalyst is highly sulfur-tolerant and more aromatic-tolerantthan Pd-Pt/USY catalyst under hydrogenation reaction conditions.