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Abstract

Heating up a Pt(100) surface with coadsorbed NO + CO leads to the evolution of CO₂ + N₂ in an extremely narrow temperature range near 400 K. A systematic investigation of this effect was performed by means of LEED, work function measurements and mass spectrometry. Our results combined with previous TDS work of other authors allowed proposal of a new model for the autocatalytic CO₂ peaks. Their occurrence can be explained by a simple vacancy model for the rate-limiting step of NO dissociation, if one takes into account the effect of island formation of the adsorbed phase. Since both adsorbates, NO and CO, lift the hex reconstruction, their coadsorption leads to the formation of mixed 1 × 1 islands with a constant local coverage. Solution of a set of differential equations describing the kinetics of the individual steps reproduces well the experimental observations.