HYDROGENATION OF VINYLBENZENES ON PD-TM AL2O3 AND TM/AL2O3 CATALYSTS/

Pd-Tm/gamma-Al2O3 catalysts containing 0.1% Pd-1% Tm, 0.3% Pd-1% Tm an d 0.5% Pd-1.% Tm, respectively have been obtained by successive impreg nation of gamma-Al2O3, first with palladium and then with thulium. Int roduction of Tm leads to an increase in the conversion of vinylbenzene s compared to that with monometallic Pd/gamma l-Al2O3 catalysts. For m onocomponent Pd/gamma-Al2O3 catalysts, turnover frequency (TOF) is unc hanged. For bicomponent Pd-Tm/gamma-Al2O3 catalysts, if one considers that the reaction occurs only on the Pd particles, then introduction o f Tm seems to increase the TOF. However, by taking Tm into considerati on when calculating the TOF, then the bicomponent catalysts are seen t o behave as the monocomponent catalysts. This behaviour is highlighted also by using the Koros-Nowak criterion. If Tm is not considered to b e an active species, vinylbenzene hydrogenation appears to be controll ed by mass transfer processes. However, the texture characteristics of the bicomponent catalysts are not sufficiently modified by Tm introdu ction to support such a hypothesis. On the contrary, by considering th e Tm participation in the reaction, the slope of the Koros-Nowak depen dence is included in a range typical for kinetically controlled reacti ons.