Abstract: A series of supported palladium catalysts were prepared with impregnating method. SO_4~(2-) was introduced by dipping Al_2O_3 into dilute H_2SO_4 solution for the preparation of Pd/Al_2O_3--SO_4 or impregnating Pd/Al_2O_3 with a series of K_2SO_4 solutions for Pd/SO_4~(2-)/Al_2O_3 as catalysts. X-ray photoelectron spectroscopy was employed to measure the states of sulfur and palladium before and after the catalysts were treated under different atmospheres. Temperature programmed desorption-mass spectroscopy (TPD-MS) was used to investigate the effect of different sulfur species and atmosphere on H_2 adsorption on the catalysts. The results showed as follows: The influence of sulfur species upon H_2 desorption declined in a order as S_2~(2-), S~(2-) and SO_4~(2-), and the effect of the former two was more distinct than SO_4~(2-). Their behaviors were in accord with the evaluation of the catalyst for H_2-O_2 reaction, which may be interpreted with the molecular orbital theory.

Key words: Pd/Al₂O₃ catalysts, Sulfur species, H₂ adsorption, α、β₁ and β₂ adsorbed hydrogen