Effects of preparation methods on the catalytic performance of Ni/CeO₂-Al₂O₃ catalyst in methane partial oxidation

A series of Ni/CeO₂-Al₂O₃ catalysts were prepared by the methods of impregnation-precipitation, hydrothermal synthesis, co-precipitation and citric acid complexation. The effects of preparation method on the physical structures and catalytic performance of the resultant catalysts in partial oxidation of methane (POM) were investigated. The fresh and spent catalysts were characterized by N₂ physical adsorption, X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H₂-TPR), temperature programmed desorption of ammonia (NH₃-TPD) and thermogravimetry (TG) analysis. The results show that Ni/CeO₂-Al₂O₃ prepared by impregnation-precipitation method exhibits the lowest activity and selectivity to H₂ and CO; the highest catalytic performance is achieved by the catalyst prepared through citric acid complexation. The Ni/CeO₂-Al₂O₃ catalyst prepared by citric acid complexation has the largest specific surface area and the smallest CeO₂ crystals with good dispersion. Both Ni species and NiAl₂O₄ spinel in Ni/CeO₂-Al₂O₃ prepared by citric acid complexation are prone to being reduced to metal Ni, which can produce more active sites for methane partial oxidation reaction. There is more acidic sites and deposited carbon over the catalyst prepared by citric acid complexation; however, taking its high activity into account, its stability is relatively high with low carbon deposition rate.