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LEED and AES studies of LaNi5 single crystals cleaved in UHV and exposed to oxygen and hydrogen show that surface segregation of La is induced at room temperature by oxygen, but not by hydrogen. This segregation is driven by the chemical exchange reaction (La-Ni)+O→ (La-O)+Ni. A surface-layer model is derived supporting the important implications of the segregation for the excellent kinetics in hydrogenation and the resistance to contaminants.
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Waldkirch et al. (1978) studied this question.
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