Abstract:

A series of Pd-containing hydrotalcite precursors (M3Al-HT) with different M2+ (M=Mg, Co, Ni, Cu, Zn) ions were synthesized by a co-precipitation method. Pd/M3AlO catalysts were derived from these hydrotalcite-like compounds by calcination. X-ray Diffraction (XRD), thermogravimetry-differential thermal gravimetry (TG-DTG), N2 adsorption and desorption, temperature programmed reduction (H2-TPR), and temperature programmed desorption (O2-TPD) techniques were used to study the influence of different M2+ ions on the composition and structures of the Pd/M3AlO catalysts and their performance during the catalytic oxidation of chlorobenzene. XRD and TG-DTG data showed that hydrotalcite precursors could be successfully prepared with different M2+ ions except Cu2+ ion. And Pd was well dispersed in different hydrotalcite precursors. The M2+ ions greatly influence the activities of the serial catalysts. Among the investigated catalysts, the activity of the Pd supported Co-containing oxide was found to be much higher than the other catalysts. The light-off and complete oxidation temperatures were 182 and 283 ℃, respectively. H2-TPR and O2-TPD results show that higher reduction abilities and higher intensities of the surface oxygen active species as well as the synergetic effect between Pd and Co contribute to excellent Pd/Co3AlO catalytic activity.

Key words: Hydrotalcite, Palladium, Mixed oxides, Catalytic oxidation, Co-precipitation