TOLUENE HYDROGENATION OVER SUPPORTED PLATINUM CATALYSTS

The specific activity for toluene hydrogenation on supported Pt depended on the support utilized and followed the sequence: Pt/SiO2-Al2O3 > Pt/TiO2 > Pt/Al2O3 congruent-to Pt/SiO2. The activation energy was independent of the support and had an average value of 12 kcal/mol. The apparent reaction order on hydrogen was found to be independent of the support and increased from 0.7 at 333K to over unity at 373K, whereas the reaction order on toluene remained near zero over the same temperature range. These results are qualitatively similar to those found previously with supported Pd catalysts except that the turnover frequencies on Pt catalysts can be more than 30 times higher. A model proposed for Pd is also applicable to Pt catalysts, that is, the enhanced activity can be attributed to a reaction between spilled-over hydrogen and toluene adsorbed on the oxide surface in the metal-support interfacial region.