Carbon Monoxide on Metals and Alloys

Figuie 8. Comparison of the fiill DFT-GGA and model dtcmisorption energies fiH-CO on a number of metal and mctal-ovniayn systems. 

Kjj between the adsorbate states and the metal d states. These quantities have been calculated from extensive quantum-chemical calculations for a significant portion of the Periodic Table. The basic idea of the Hammer-N0rskov model is that trends in the interaction and reactivity are governed by the coupling of the adsorbate states with the metal d states, since the coupling with the metal sp states is essentially the same for the transition and noble metals, and mainly acts to renormalize (i.e, shift and broaden) the energy of the adsorbate orbital. 

In the Blyholder model, CO interacts with the metal states through two different states, the 5ct and 2n orbitals, but due to their different symmetry they interact with different metal d orbitals, and the two interactions can be treated independently. Hammer, Morikawa, and N0rskov used the following expression to model the dcontribution to the CO chemisorption energy  

The same model may also be used to explain why on metals in the upper-right comer of the Periodic Table (Pd, Ni) CO prefers multifold coordination, whereas towards the lower left comer (Ru, Ir) CO 

Decomposition of the Zero-Field Vibrational Frequency Shifts (in cm ) Compared to the Calculated Vacuum Values into Steric and Orbital Components for CO Chemisorbed in the Atop and Hollow SiteofPt(lll)and CO Adsorbed in the Atop Site ofRuCODOl)  

System Steric Donation Back donation Rest Final 

---