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Thesis - Oztek_Muzaffer_T_200508_MA

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Table 6. Percent hydrogen values for pure H 2 in the Parr reactor.<br />

Mole % Al P H2 , atm. Weight % H<br />

0.74 7.65 0.89<br />

1.35 7.70 0.72<br />

3.38 7.34 0.72<br />

The pressure profiles for the samples that were pressurized with 50% (v/v) H 2 :He<br />

(Figure 34) indicated that the reactions were complete also in 10 minutes. The percent<br />

hydrogen values are presented in Table 7. In the batch reactor, the rate of reaction was<br />

not affected from the presence of He. This observation suggests that, at high enough H 2<br />

pressures (7 atm in 50:50 H 2 :He mixture), the surface occupation of LaNi 5 Al x by He was<br />

not significant, compared to low H 2 pressures (5 atm). It could also be possible that the<br />

interaction of the LaNi 5 Al x with hydrogen in the presence of helium was dependent on<br />

the scale of the system. The volume of the Parr reactor was 2000 mL, as opposed to the<br />

15.37 mL of volume of the DSC cell. Also, in the Parr reactor, the sample amount was<br />

higher. Only the top layer was exposed to the He; therefore, the surface interaction of He<br />

was limited, and a reduction in reaction rate was not observed.<br />

72

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