Gas phase atomic hydrogen reacting with molecular and atomic oxygen to form water on the Pt(111) surface

Gas phase atomic hydrogen is more reactive than coadsorbed hydrogen during reaction with both adsorbed atomic and molecular oxygen on the Pt(111) surf ace. The increased reactivity of gas phase atomic hydrogen is demonstrated by complete conversion of all adsorbed molecular oxygen to water below 180 K. In contrast, coadsorbed hydrogen induces less water formation under simi lar conditions. Preferential hydroxyl formation is observed for low gas pha se atomic hydrogen exposures as evidenced by the predominance of water form ed by hydroxyl recombination at 200 K. Under these conditions the sharp red uction in the intensity of the molecular oxygen desorption peak at 150 K to gether with an increase in the atomic oxygen desorption peak at 800 K provi de direct evidence for gas phase atomic hydrogen-induced O-O bond cleavage. Adsorbed atomic oxygen is also completely converted to water at 110 K even for low exposures of gas phase atomic hydrogen. (C) 1999 Published by Else vier Science B.V. All rights reserved.