Effects of alkaline-earth strontium on the performance of Co/Al₂O₃ catalyst for methane partial oxidation

A series of Sr-Co/Al₂O₃ catalysts were prepared by co-impregnation method using γ-Al₂O₃ as the support. The effect of strontium promoter on the catalytic performance of Co/Al₂O₃ catalyst for partial oxidation of methane (POM) to synthesis gas was studied. The catalysts were characterized by some physicochemical characterizations such as N₂ physical adsorption, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR) and thermogravimetry (TG). The results show that both Co/Al₂O₃ calcined at 700℃ and Sr-Co/Al₂O₃ calcined at 800℃ exhibit low activity and deactivate at the initial stage of POM reaction. The addition of above 2% mass fraction of strontium will greatly enhance the activity and stability of Co/Al₂O₃. Two types of Co species were identified on the fresh calcined catalysts. One is Co₃O₄ which weakly interacts with Al₂O₃ (easily reduced by H₂) and the other is the spinel CoAl₂O₄ (non-catalytic performance) which strongly interacts with the support. During the course of calcination, strontium can react with Al₂O₃ to form Sr₄Al₁₄O₂₅ which will restrain the generation of the CoAl₂O₄ species and promote the stability and activity of catalysts. Without strontium promoter, CoAl₂O₄ is easy to be formed over Co/Al₂O₃ in the POM reaction. However, the formation of CoAl₂O₄ cannot be avoided with the addition of limited strontium when the calcination temperature is over 800℃.