Characterization and reactivity of alumina-supported Pd catalysts for the room-temperature hydrodechlorination of chlorobenzene

A series of alumina-supported Pd catalysts were prepared by varying the metal loading between 0.5 and 5 wt. %, adopting the deposition precipitation (DP) method. These catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), pulse CO chemisorption, Brunauer-Emmett-Teller specific surface area measurement, and transmission electron microscopy. The catalytic properties of the catalysts were studied for the hydrodechlorination of chlorobenzene. The reaction was carried out in a continuous mode passing liquid chlorobenzene and gaseous hydrogen over a fixed bed of catalyst taken in a reactor operating at room temperature and atmospheric pressure. The catalysts with metal loading up to 2 wt. % demonstrated high dispersion, homogeneous distribution of active species with predominance of metal-support interaction and without any formation of beta-PdH. Beyond 2 wt. % loading, the agglomeration of PdO took place forming bulk particles that reduced easily to metallic state displaying the characteristic negative peak in the TPR pattern. XPS measurements revealed the presence of electron deficient Pd species in the catalysts up to 2 wt. % Pd. The activity and stability of the catalysts are explained in terms of formation of the electron deficient Pd species (Pdn+) and the particle size of Pd on the surface of alumina.