The deuterium adsorption at 270 K on a reconstructed Pt(100)-hex surface covered by NOadswas studied by means of temperature programmed reaction (TPR). In the case of adsorption on a clean Pt(100)-hex surface the saturated Dadscoverage is 0.06 ML at PH2= 6 × 10-8mbar, whereas the Dadsuptake is enhanced considerably by NO pre-adsorption. First the Dadsuptake increases with increasing NOadscoverage, θNO, reaching a maximum at θNO≈ 0.25 ML, and then decreases to zero. This phenomenon is explained as follows. The NO adsorption on the hex surface leads to the formation of 1 × 1 islands saturated by NOadsand surrounded by the hex phase. The NOads/1 × 1 islands are assumed to modify the hex phase adjacent to the island boundaries, adapting this area for deuterium adsorption. TPR in the co-adsorption layer of NOadsand Dadsis initiated by D2desorption and shows an 'explosive' behaviour, manifesting itself in the narrow TPR peaks of N2and D2O at ∼370 K. The NOadspre-coverage affects the reaction temperature as well. Thus, at NOadscoverage of 0.35-0.40 ML the temperature of the surface explosion increases abruptly by ∼15-20 K. At this coverage the NOads/1 × 1 islands are supposed to modify the rest of the hex phase so that, after further D2adsorption, the surface becomes completely saturated by Dadsand NOadsspecies. A possible mechanism for this is discussed. © 2000 Elsevier Science B.V. All rights reserved.
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