Abstract
The carrier effects on the catalytic activity and the physical properties of supported palladium catalysts were investigated. The catalytic activity was evaluated by hydrogenation of benzene and physical properties of catalysts were probed with CO pulse method, transmission electron microscopy (TEM), electron probe microanalysis (EPMA), temperature programed reduction (TPR) and temperature programed desorption (TPD). The Pd/Al2O3catalysts were prepared by the adsorption method using dilute HCl solution (0.1 M to 1.0 M)of PdCl2 and the Pd/SiO2 catalysts by the ion exchange method using aqueous am monia solution of PdCl2. The Pd/Al203 catalyst calcined at 500°C showed high activity and high dispersion, while th e Pd/SiO2 catalyst calcined at 200°C exhibited highest activity and high dispersion. However, the catalytic activity and the palladium surface area of the Pd/SiO2 catalyst decreased with the increased of the calcination temperature. The specific catalytic activity of Pd/Al2O3was roughly three times as high as that of Pd/SiO2. The strong interaction between metal and support and a large amount of adosrbed hydrogen were revealed by TPR and TPD measurements in the case of Pd/Al2O3 catalyst. Palladium oxide formed on SiO2 was easily reduced with hydrogen even at room temperature just as unsupported palladium oxide and the formation of palladium hydride was confirmed by TPR measurements. The nature of active sites produced on both supports was discussed from the stndpoint of carrier effects.
