Intermetallic compounds CeNis

Simultaneously, the synthesis of ammonia from the elements was also tested over RE-TM intermetallic compounds by the same group (42). Here, 36 intermetallic compounds of rare earth elements and the transition metals Fe, Co, and Ru were evaluated. In the case of the ammonia synthesis, the rare earth component is transformed to the corresponding nitride and the transition metal is finely divided thereon. Some of the compounds showed an even higher specific activity than commercial catalysts used at that time. Later, the catalysts based on the intermetallic compound CeNis-j Cox (x = 0-5) were oxidized in a controlled way prior to the catalytic characterization in the Fischer-Tropsch reaction (43). The reasons to oxidize the compound before use were twofold. On the one hand, the material can be handled in air afterwards, whereas the intermetallic compound itself is not stable in air. Second, the oxidation can be better controlled and reproduced if it is not performed in situ. A review on the early work on these catalysts is available by Wallace (44). 

Imamura and Wallace (1980) used various intermetallic compounds (LaNis, CeNis, ThNis, TI1C05) as precursors. After decomposition under oxygen at 350°C they obtained catalysts which were clearly more active than the corresponding classical Ni catalysts. They suggested that geometrical effects were responsible for such a behavior. 

It is also interesting to note that the decomposition of pseudobinary intermetallic compounds (LaNi4Fe and CeNis-jCo ) leads to the formation of bimetallic transition metal particles which display different selectivities than the catalysts derived from the related binary intermetallic compound (Paul-Boncour et al. 1991, France and Wallace 1988). The characterization of the bimetallic particles by XRD, Mossbauer spectroscopy and magnetism indicated that their composition was close to that of the starting alloy. 

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