Thesis - Oztek_Muzaffer_T_200508_MA

3.2.2.4. AuPd and Pt Coating on LaNi 5
The reduced reaction rate for the H 2 -LaNi 5 system was determined to be the
inhibition of transport of H 2 to the LaNi 5 surface. The dominance of He on the surface
eventually left less surface for H 2 absorption. On the other hand, the capacity was not
highly affected due to the fact that interaction of the metal with H 2 was inhibited only at
the surface.
Gold-palladium (AuPd) and Platinum (Pt) are known to be used as catalysts
facilitating hydrogen dissociation in hydrogenation reactions. The dissociation and
transport of H 2 is expected to be high on these catalysts. Therefore to overcome the
inhibition of rate when He is present (i.e. enhance H 2 dissociation on the surface), the
samples were coated with AuPd and Pt.
The percent hydrogen values for LaNi 5 with 12 and 0.77% Al at different
hydriding pressures are given in Table 5. The types of coating and percent hydrogen
values for non-coated samples as reference are also listed.
The amount of hydrogen absorbed from 50% (v/v) H 2 -He mixtures increased as
AuPd coating times increased. The percent hydrogen was still less than the value
obtained from pure H 2 at the same pressure. However, the capacity loss in the presence of
He was restored for Pt coated samples.
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