Effects of atmosphere pretreatment on the catalytic performance of Pd/γ-Al2O3 catalyst in benzene degradation II: Crystal structure transformation of Pd active species

Abstract The effects of pretreatment under reducing (H 2 ), inert (N 2 and He), and oxidative (air) atmospheres on the catalytic performance of Pd/γ-Al 2 O 3 in benzene degradation were investigated in this study. The crystal structure transformation of Pd active species, which is a significant influencing factor on the catalytic activity of Pd/γ-Al 2 O 3 , was investigated in depth via X-ray diffraction combined with in situ Raman analysis. Results showed that the temperature-induced destruction of the near-surface PdO crystal lattice occurs at or above 553 K in inert pretreatment, and this process is reversible when the temperature decreased immediately. The destruction of the PdO crystal lattice largely relied on the increase in treatment time, resulting in the structural transformation from the well-defined crystalline PdO to the amorphous state. The temperature-induced destruction of the near-surface PdO crystal lattice was also observed in oxidative atmosphere with no connection with the increase in treatment time. The catalytic performance of Pd/γ-Al 2 O 3 on benzene degradation is enhanced significantly as a result of the structural transformation from the well-defined crystalline PdO to the amorphous state via pretreatment with inert atmosphere. A possible mechanism for the structural transformation process and its relationship with the catalytic activity is proposed.