ELECTROCHEMICAL PROMOTION OF THE Pt/CO + NO REACTION
479
of CO(a) and the EP effect should be small, as is indeed the applied potential and to precisely tune the promoter
observed. At high PCO the EP effect is also attenuated. coverage on catalyst surfaces allows for a systematic study
The sharp changes in activity (Fig. 6a) which occur as of the role of promoters in heterogeneous catalysis.
a function of PNO at fixed potentials of ꢃ200 mV and
+200 mV resemble the behavior observed for the CO + O2
reaction over Pt/ꢀ00 alumina (5) and we propose an anal-
ogous explanation. At low PNO the surface is dominated
by islands of CO; reaction occurs only at the peripheries
of these islands, resulting in a low rate. At sufficiently high
ACKNOWLEDGMENTS
A.P. holds a CONICET Postdoctoral Research Fellowship. A.P. and
R.M.L acknowledge support by the British Council and Fundacio´n Antor-
chas. Additional support under British Council Grant ATH/882/2/FUEL
and from the Hellenic Secretariat EPET-II Programme is also gratefully
PNO the CO islands are disrupted by NO chemisorption, in acknowledged.
effect a 2D phase transition, and the rate rises sharply as
intermixing of the reactants occurs. This model is strongly
supported by the observed effects of Na promotion. The
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2
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rN O results in Figs. 6b and 6c are similarly understandable.
2
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2
2
ically higher as the Na coverage becomes more negative in
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CONCLUSIONS
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2. Under all conditions, the selectivity toward N2 forma-
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4. The ability of solid electrolytes, such as ꢀ-00Al2O3, to
(1982).
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