NO and deuterium co-adsorption on the reconstructed Pt(100)-hex surface: A temperature programmed reaction study

Abstract

The deuterium adsorption at 270 K on a reconstructed Pt(100)-hex surface covered by NOads was studied by means of temperature programmed reaction (TPR). In the case of adsorption on a clean Pt(100)-hex surface the saturated Dads coverage is 0.06 ML at PH2 = 6 × 10-8 mbar, whereas the Dads uptake is enhanced considerably by NO pre-adsorption. First the Dads uptake increases with increasing NOads coverage, 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 NOads and 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 NOads and Dads is initiated by D2 desorption and shows an 'explosive' behaviour, manifesting itself in the narrow TPR peaks of N2 and D2O at ∼370 K. The NOads pre-coverage affects the reaction temperature as well. Thus, at NOads coverage 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 D2 adsorption, the surface becomes completely saturated by Dads and NOads species. A possible mechanism for this is discussed. © 2000 Elsevier Science B.V. All rights reserved.