Paper EN-TuP2
A Closer Look at H-CO Interaction on the Platinum Surface

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

The system comprised of coadsorbed hydrogen and carbon monoxide on platinum has been the subject of a number of experimental work due to its high relevance in heterogeneous catalysis, particularly in relation with hydrogen fuel cells. Several studies have asserted the strong repulsion between these two species on the solid surface, especially in high pressures, wherein the formation of homogeneous islands of CO have been reported. On the other hand, theoretical work specifically addressing the H/CO coadsorption system on Pt is rather limited. To fully understand the physical mechanisms involved at the atomic scale, it would be beneficial for example to quantify the extent to which H and CO interaction on Pt is repulsive, knowing that H-CO interaction in the gas phase is actually partly attractive, and comment on possibilities for H and CO closely coexisting on Pt. It is in this light that we in this study describe the behavior of hydrogen near a Pt surface-adsorbed carbon monoxide molecule using a potential energy term constructed from ab initio calculations. The considerable asymmetry of the repulsion extent around CO suggests that while incoming hydrogen experiences strong obstacles to adsorption even before the Pt surface is reached, adsorbed H can remain stable even in relatively compact conditions. Inhibiting effects of CO greater than what is expected from simple adsorption site exclusion are discussed with regard to adsorption/desorption and mobility on platinum, as well as possibilities of COH and HCO formation on platinum. A quantum mechanical treatment of the H atom behavior similar to what we have used before¹ is also performed on the obtained potential term. Theoretical results are lastly discussed with available experimental data on the H-CO coadsorbate system on transition metal surfaces.

¹T. Roman, H. Nakanishi, W. A. Diño, H. Kasai, e-J. Surf. Sci. Nanotech. 4 (2006) 619.