The effect of Ni-Al ratio on the properties of coprecipitated nickel-alumina catalysts with high nickel contents

A series of nickel-alumina catalysts with a Ni/Al ratio between 3 and 20 has been prepared by coprecipitation. The calcination and reduction of these samples have been studied by thermogravimetry and their structures after calcination and reduction at different temperatures has been examined by X-ray diffraction. The methanation activities of the final catalysts have been determined by differential scanning calorimetry. Whereas the alumina present in the samples with Ni/Al = 3 stabilises the catalysts against crystalline growth during both calcination and reduction, the effect is much less pronounced with higher nickel contents. The resultant catalysts for Ni/Al = 6, 9 and 20 were found to have activities comparable with those with Ni/Al = 3 as long as the calcination and reduction are carried out at relatively low temperatures. A model of the catalysts is proposed.