Study Of Stability On Nickel-Based Catalysts For Syngas To Methane

Synthesis of methane from syngas is under the conditions of high CO concentration [（CO+CO₂）≥25%],300-600℃ and 1-3 MPa is a strong exothermic reaction, the byproduct water will be produced with water vapor concentration up to 50% theoretically.High temperature and high moisture concentration can destroy the structure of the catalyst. The study of stability for support and catalyst is very necessary to find a stable catalyst under such conditions.In this paper, water vapor concentration, supports and promoters on the catalytic behaviors of nickel-based catalysts in the methane synthesis were investigated. The catalysts were characterized by X-ray diffraction, Scanning electron microscope,-N2 adsorption-desorption. Meanwhile the reasons of Ni/γ-Al₂O₃ catalyst deactivation were explored. Main results are as follows.Catalytic behavior for methanation from syngas over nickel-based catalysts with γ-Al₂O₃ under different water vapor concentration was investigated. Characterization results showed that γ-Al₂O₃ hydration may be the main factor which influences the stability of catalysts. The stable time of the catalyst was inversely proportional with the concentration of water vapor of the system. γ-Al₂O₃ hydration phase transition led to the deactivation of the catalyst.The Ni-Mn/γ-Al₂O₃ catalysts were prepared by impregnation method. Characterization results showed that Mn mainly exists in the form of MnO₂-Mn addition inhibits nickel grain growth and improved the stability of catalyst. But the addition of Mn can’t fundamentally solve the problem of hydrothermal deactivation of catalyst.Effects of magnesium aluminum ratio, calcination temperature on crystal phase structure, specific surface area, hydrothermal stability of magnesium aluminum composite oxide and catalytic behavior for methanation from syngas over nickel-based catalysts with support MgAl2O4 was investigated. The experiment result indicates MgO/Al₂O₃ =0.395, magnesium aluminum composite oxide as the pure magnesium aluminium spinel phase which have good hydrothermal stability. MgO/Al₂O₃ reduced from 0.395 to 0.05, the specific surface area of magnesium aluminum mixed oxide from 97.8 m2/g increases to 196.1 m2/g. When other conditions are the same, the stability of Ni/MgO-Al₂O₃ synthetic methane is better than Ni/y-Al₂O₃.