The preparation and pretreatment of coprecipitated nickel-alumina catalysts for methanation at high temperatures

The preparation and properties of a series of coprecipitated nickel-alumina catalysts have been examined. For 2 ⩽ Ni/Al ⩽ 3, the precipitate has a layer structure of the type previously described by Feitknecht and by Longuet-Escard. Our results indicate that the nickel and aluminium ions occupy interchangeable positions in the “brucite-type” layers of the structure, while various anions (CO⁼₃, NO^‐₃, or Cl^‐, depending on the method of preparation) are found in the “interlayer” in addition to water to crystallisation. On calcination, poorly crystallised nickel oxide, which probably contains dissolved Al³⁺ ions, is formed; the crystallinity of this phase depends strongly on the ions present in the precipitate. Phase separation of NiAl₂O₄ occurs at temperatures around 1000 K. The metallic surface areas and the methanation activities of the reduced samples depend directly on their degree of reduction; for identical calcination and reduction conditions, it is found that samples originating from the carbonate containing precipitates have higher activities under methanation conditions than the nitrates or chlorides. The presence of sodium has a detrimental effect on the properties of the catalysts.