Mechanisms on gold particle only

The principal difficulty with metal only mechanisms is to find a plausible way of activating the oxygen molecule. The problem is discussed in Section 5.2.2 formation of the Oj ion, in which the 0-0 bond is considerably weakened (see Table 5.2), appears possible on small particles,130,131 and the suggestion that the adsorption of oxygen and of carbon monoxide is mutually supportive opens a possible route for a metal-only mechanism. 

The Au/MgO and Au/Mg(0H)2 systems have received considerable experimental attention, both with real (Section 6.3.3.7) and model catalysts,132-135 and theoretical calculation129,136-139 due no doubt to the structural simplicity of the support. DFT calculations on Aui2 and AU34 particles and on stepped Au(211) and (221) surfaces lead to the proposal of 

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The study on Au/TiO2(110) model catalyst performed by Goodman et al. [10] is the first study to lead to the proposal of a reaction mechanism on gold particles only . According to these authors when gold metal particles are small enough and bi-dimensional (Section 15.4.1), they lose their metallic properties due to the quantum size effect (band gap of 0.2-0.6eV), and become an active catalyst (Fig. 15.6). The role of the support would be to stabilise the small gold particles. 

These calculations point out an important feature, that the interface plays a key role for the activation of O2 even though the support is non-reducible, and that the mechanism on gold particles only requires the assistance of the support to create... 

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