Fig. 1 Temperature-dependent CO removal and H2 loss characteristics of representative catalysts

The highest CO removal efficiency is seen to have been obtained over a wide temperature range with Ru-base catalyst. As regards hydrogen loss, all catalysts have tended to raise their effectiveness with increasing temperature. In this respect, Ru-base catalyst is at a disadvantage for its diminishing hydrogen at a rapidly rising rate with increasing temperature, thus taking away hydrogen that could serve usefully as fuel.

(2) Parasitic reactions of catalyst

Conceivable parasitic reactions that might be induced by catalyst include reverse-shift reaction, methanation and hydrogen oxidation. To examine such possibility, the temperature-dependent behavior of Ru-and Rh-base catalysts were examined on a simulated reformate gas devoid of CO.

The results, indicated in Fig. 2, reveal that with such gas initially devoid of CO, Rh-base catalyst generates CO by reverse-shift at high temperature. Such reaction is not induced by Ru-base catalyst, but on the other hand, this catalyst generates CH4 by methanation of CO2. While CH4 does not directly detract from PEFC performance, its generation is at the expense of consuming fuel hydrogen, and should thus be minimized.

Entrance Gas Components - C02 :1.8%; H2 : 6.0%; N2 : Balance Testing conditions: SV: 20,000 hr"1; LV: 0.22 Nm/s Exit gas component plots:




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