BISMUTH ADSORPTION ON PT(110) AND THE COADSORPTION OF CARBON-MONOXIDE

The adsorption of bismuth on Pt(110)-(1 x 2), and its coadsorption with CO, has been investigated using TPD, XPS, LEED and work function measurements. Bismuth adsorption lifts the (1 x 2) surface reconstruction at coverages theta(Bi) > 0.3. The adsorbate induced lifting of the clean surface reconstruction is activated, and annealing the surface above 350 K results in more complete ordering and the formation of. a series of ordered bismuth overlayers on Pt(110)-(1 x 1). At theta(Bi) = 0.5, a c(2 x 2) structure is observed. LEED measurements indicate that higher coverages are achieved by a uniaxial compression of this centered overlayer structure, subsequently converting above theta(Bi) = 0.7 to a (3 x 1) and streaked (4 x 1) structure. Saturation coverage is estimated to be theta(Bi) = 0.75. Bismuth blocks CO adsorption through a local, short range interaction, resulting in a linear decrease in CO coverage with increasing bismuth coverage. CO adsorption is completely poisoned at the saturation coverage of theta(Bi) = 0.75. Coadsorption of low coverages of bismuth with CO produces a new, c(2 x 4) structure which we associate with an ordered mixed phase of the adsorbates with theta(CO) = 0.5 and theta(Bi) = 0.25. At higher coverages of bismuth, the co-adsorbed CO phase does not disrupt the ordered bismuth layers observed in the absence of CO. Bismuth adsorption also favours the desorption of CO from the low temperature (alpha) desorption peak, which we associate with repulsive interactions.