Catalytic combustion of methane in simulated PSA offgas over Mn-substituted La-Sr-hexaaluminate (La_xSr_1-xMnAl₁₁O ₁₉)

Mn-substituted La, Sr-hexaaluminate was studied as a catalyst for the catalytic combustion of pressure swing adsorption (PSA) offgas from a hydrogen station based on steam reforming of petroleum gas. The catalytic activity and thermal stability were tested under simulated PSA offgas condition and the catalysts were characterized by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), CO₂-temperature programmed desorption (TPD) and N₂ physisorption for BET. All the La_xSr_1-xMnAl₁₁O₁₉ catalysts prepared by co-precipitation method contained hexaaluminate structure as the major phase after 5 h calcination at 1200 °C. Partial substitution of La for Sr in SrMnAl₁₁O₁₉ increased the specific surface area and consequently the catalytic activity for oxidation of methane. The CO₂ in the simulated PSA offgas was found to suppress the catalytic activity in methane oxidation if the catalyst had appreciable surface basicity. The most active catalyst, La_0.6Sr_0.4MnAl₁₁O ₁₉, retained its lattice structure and chemical composition even after 40-h thermal aging at 1000 °C under PSA offgas composition.