Spillover effects induced by rare-earth metals on Pd/γ-Al2O3 in vínylbenzenes hydrogenation

Pd-Ln/γ-Al 2 O 3 (Ln-Sm, Gd, Dy, Ho, Tm) catalysts containing 0.1%Pd- 1%Ln, 0.3%Pd -1% Ln and respectively, 0.5% Pd -1% Ln (percentage in wt.%) were investigated. Introduction of Ln leads to an increase of the vinylbenzenes conversion comparatively with monometallic Pd/γ-Al 2 O 3 catalysts. The turnover frequency (TOF) calculus of the latter catalysts suggests that there are no difference among these. In the case of bicomponent Pd-Ln/γ-Al 2 O 3 catalysts, if one considers that the reaction occurs only on the palladium particles, then introduction of Ln seems to increase the TOF and vinylbenzenes hydrogenation seems to be, controlled by the mass transfer processes as indicated by the Koros-Nowak criterion. However, by taking Ln into consideration when calculate the TOF, it results that bicomponent catalysts behave like those monocomponent and the slope of the Koros-Novak dependence is included in a range typical for kinetically controlled reactions. This behavior could be associated to direct participation of Ln to reaction using hydrogen spilled over from the palladium particles.