The effect of support properties on the activity of Pd/C catalysts in the liquid-phase hydrodechlorination of chlorobenzene

Abstract

The activity of palladium catalysts prepared using active carbons (AG-2000, MeKS) and Sibunit type carbon in the liquid-phase hydrodechlorination of chlorobenzene has been studied. The use of AG-2000 activated carbon prepared from coal raw material provided the highest initial activity of the catalyst ( 9.4 mo l C 6 H 5 Cl /mo l Pd min for the catalyst with particle size of 0.08–0.1 mm) which not reduced within next 4 cycles. However, this activity cannot be explained only on the basis of support texture characteristics. From results of chemical analysis as well as X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR TEM) data the high activity of the Pd/AG-2000 catalyst is explainable by the presence on the surface of the initial activated carbon of oxygen-containing compounds of iron, aluminum, silicon, calcium and magnesium. The overall ash content of the activated carbon was 11.9 wt.%. It can be assumed that the oxide compounds of iron act as anchoring centers for palladium, and that oxide containing impurities may interact with HCl decreasing deactivation. The experimental data of this work has shown that the main contribution to the Pd/AG-2000 catalyst activity is made by the palladium particles with a size of 3 nm and higher which remain stable under the aggressive conditions of the chlorobenzene hydrodechlorination process.