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

The deuterium adsorption at 270 K on a reconstructed Pt(100)-hex surface co vered 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 D -ads coverage is 0.06 ML at P-H2 = 6 x 10(-8) mbar, whereas the D-ads uptak e is enhanced considerably by NO pre-adsorption. First the D-ads uptake inc reases with increasing NOads coverage, theta(NO), reaching a maximum at the ta(NO) approximate to 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 x 1 islands saturated by NOads and surrounded by the hes pha se. The NOads/1 x 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 D-ads is initiated by D-2 desor ption and shows an 'explosive' behaviour, manifesting itself in the narrow TPR peaks of N-2 and D2O at similar to 370 K. The NOads pre-coverage affect s the reaction temperature as well. Thus, at NOads coverage of 0.35-0.40 ML the temperature of the surface explosion increases abruptly by similar to 15-20 K. At this coverage the NOads/1 x 1 islands are supposed to modify th e rest of the hex phase so that. after further D-2 adsorption, the surface becomes completely saturated by D-ads and NOads species. A possible mechani sm for this is discussed. (C) 2000 Elsevier Science B.V. All rights reserve d.