Nickel Catalysts for Steam Reforming and Methanation

Kruissink, Van Reijen, and Ross56 described the results of a detailed investigation of the structure of the coprecipitate and the effect of pH and Ni/Al ratio on this structure. They showed that the precipitate consists of brucite-like layers of compositions [Ni A (OH)2 ] x)+ and interlayers 

Allmann and H. P. Jepsen, Neues Jahrb. Mineral. Monatsh., 1969, 544 R. Allmann, Acta Crystallogr., Sect. B, 1968, 24, 972. 

Kruissink et al.56 confirmed the earlier observation of Beecroft et al.s5 that the decomposition of the precipitate occurs in two steps. In the first, between 130 and 230 UC, depending on the anion, the molecular water is removed from the interlayer and there is a slight decrease in the interlayer spacing. The brucite layer is destroyed at a higher temperature ( 350°C) with the evolution of water (from the OH-ions) and for example, C02 or N02, depending on the anions in the coprecipitate. 

The nature of the anion in the coprecipitate can have a marked effect on the behaviour of the final catalyst, particularly if the heating rate is not carefully controlled in such a way that the gases evolved during the 

COl N03 eland that the stabilities of the catalysts during reaction in a CO + 3H2 mixture at 500 °C fell in the same order. It was concluded that the main effects of the anions were manifested during the calcination of the coprecipitates. It was also observed that the hydrothermally aged materials gave reduced samples with very similar methanation activities to those derived from the freshly prepared materials. 

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