Role of acidity of catalysts on methane combustion over Pd/ZSM-5

Palladium-based catalysts were prepared by the impregnation (I) and ion-exchange method (E) with ZSM-5 and γ-Al2O3 as support respectively. The high activity of Pd/ZSM-5(I) and Pd-ZSM-5(E) catalysts for methane combustion was observed. The order of activity is consistent with Brønsted acidity of catalysts: Pd/ZSM-5(I) > Pd-ZSM-5(E) > Pd/Al2O3. It is shown by FT-IR that methane adsorbs on acidic bridging hydroxyl groups of ZSM-5-supported Pd catalysts. Symmetric v1 C–H stretching vibrations of methane shift to low frequency due to the interaction between methane molecules and Brønsted acid sites or Pd2+, indicating that methane molecules can be activated.