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 NO ads was studied by means of temperature programmed reaction (TPR). In the case of adsorption on a clean Pt(100)- hex surface the saturated D ads coverage is 0.06 ML at P H 2 =6×10 −8 mbar, whereas the D ads uptake is enhanced considerably by NO pre-adsorption. First the D ads uptake increases with increasing NO ads coverage, θ NO, reaching a maximum at θ NO≈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 NO ads and surrounded by the hex phase. The NO ads/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 NO ads and D ads is initiated by D 2 desorption and shows an ‘explosive’ behaviour, manifesting itself in the narrow TPR peaks of N 2 and D 2O at ∼370 K. The NO ads pre-coverage affects the reaction temperature as well. Thus, at NO ads coverage of 0.35–0.40 ML the temperature of the surface explosion increases abruptly by ∼15–20 K. At this coverage the NO ads/1×1 islands are supposed to modify the rest of the hex phase so that, after further D 2 adsorption, the surface becomes completely saturated by D ads and NO ads species. A possible mechanism for this is discussed.