The Electronic Factor in Heterogeneous Catalysis

1 THE /-BAND MODEL OF CHEMICAL BONDING AT TRANSITION METAL SURFACES 

Fundamental Concepts in Heterogeneous Catalysis, First Edition. Jens K. N0rskov, Felix Studt, Frank Abild-Pedersen and Thomas Bligaard. 

FIGURE 8.1 Schematic illustration of the interaction between an adsorbate valence level and the delocalized -states and localized rf-states of a transition metal surface. 

FIGURE 8.2 Calculated -projected density of states (DOS) for a number of platinum clusters in the cuboctahedron structure. The figure clearly shows the transition between a continuous band structure of highly delocalized electrons for large clusters ( 2nm) and the more discrete energy levels for smaller clusters. For comparison, the ealculated s-projeeted DOS for Pt( 111) is shown as well. We note the resemblance between the DOS for the Pt and the Pt(lll) slab, suggesting that already at sizes above 2nm, the band structure is close to converge to the metallic state. 

In this picture, we can write the adsorption energy in the simple form  

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Interest in studying formic acid adsorption on metals by XPS and UPS was stimulated largely by its use as a probe molecule for investigating the role of the electronic factor in heterogeneous catalysis as in the work of Schwab (70), Dowden and Reynolds (71), Eley and Leutic (72), and Fahren-fort et al. (73). The advantages of XPS and UPS are fourfold. 

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