The Quantum-Chemical View of Bond Activation

1 Activation of the Molecular ji Bond (Particle Shape Dependence) 

The change of activation barrier of CO by altered surface topology is substantial. In the case of CO, activation by Ru is more than 100 kj mol . Similar large changes are found for other transition metals. The phenomenon is general. Similar large changes are found for activation of other diatomic molecules with K bonds as Nj, NO, or O2. 

We discuss here the chemical bonding aspects that determine this surface topology dependence. 

It is discussed in Section 10.3.2 that when a molecule as CO adsorbs to the surface the antibonding 27t orbitals becomes partially occupied by electrons because of backdonation from the metal surface. This weakens the internal C-O bond strength. The stronger the covalent interaction with the surface, the more weakened the C-O bond in the adsorbed CO molecule. 

Similarly as on a step-edge site, dissociation of tr-bonded molecules on the square (100) surface ofan fee crystal becomes substantially lower than on the (111) surface. 

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