EFFECT OF HF PRETREATMENT ON H-2 REACTIVITY WITH LANI5 AND LANI4.7AL0.3

The effect of fluorination of LaNi5 and LaNi4.7Al0.3 surfaces on the i nitial activation of hydrogen absorption was examined at 298 K by the measurement of H-2 reaction probability under ultra high vacuum and lo w vacua conditions, and by the measurement of the initial rate of hydr ogen absorption at pressures over 10(6) Pa. The HF pretreated LaNi4.7A l0.3 and LaNi5 alloys degassed up to ultra high vacuum, and no improve ment or even a marked reduction in the H, reaction rate was observed. However, the HF pretreated LaNi4.7Al0.3 degassed at low vacuum exhibit ed a much higher reactivity than the sample degassed in ultra high vac uum. The results obtained show the importance of alumina present in th e fluorination, and a possible enhancement of catalytic properties by the oxidation of fluorinated LaNi4.7Al0.3.