Strong effect of transitional metals on the sulfur resistance of Pd/HY-Al2O3 catalysts for aromatic hydrogenation

In order to improve the sulfur resistance of noble metal catalysts in the a romatic hydrogenation of diesel fuel, the alloying effect of non-noble meta ls with Pd was studied. Toluene hydrogenation over Pd and Pd-M bimetallic c atalysts (M = Cr, W,La, Mn, Mo, Ag) on a mixed HY-Al2O3 support was investi gated in the presence of 3000 ppm sulfur as thiophene in the feedstock. The results showed that the addition of the second metals strongly affected th e activity of toluene hydrogenation, which suggests that the sulfur resisti bility of Pd-M bimetallic catalysts is much different from single Pd. La, M n, Mo and Ag decreased the sulfur resistance of the palladium catalysts. Fo r example, the toluene conversion at 553 K was observed to decrease sharply from 39.4 wt.% on Pd to 1.6 wt.% on Pd-Ag, which is by a factor of 25. One of the important findings in this article is that Cr and W increase hydrog enation activity of Pd catalysts. The reactions occurring on these catalyst s include hydrogenation, isomerization and hydrocracking, The addition of t he second metals has no noticeable effects on the hydrogenation and isomeri zation selectivity, but it slightly suppresses hydrocracking reactions. The four typical catalysts, Pd-Cr, Pd-W, Pd-Ag and Pd were characterized by in frared (IR) spectroscopy of pyridine and CO. LR spectra of CO revealed the strong interaction between Pd and the second metal as Cr, W and Ag (or thei r oxide), indicating that the improvement in sulfur resistance originates f rom electron-deficient Pd with the addition of second metals. (C) 2001 Else vier Science B.V. All rights reserved.