Harutas Mechanism Metal Gold Particles

Two mechanisms of CO oxidation reaction among those proposed in the Introduction (Section 15.1) involve reducible oxide supports Haruta s mechanism with fully metallic gold particles (Fig. 15.2) and Bond and Thompson s mechanism involving unreduced gold species at the metal-support interface (Fig. 15.3). 

This mechanism is consistent with a Langmuir-Hinshdwood mechanism with a reaction between adsorbed CO and O2 molecules as the rate-limiting step, based on kinetics studies performed on Au/Ti02 catalysts [33, 56, 70, 73] and IR studies 

It may be noted that surface formates arising from the interaction between CO and surface hydroxy groups have also been proposed as reaction intermediates [73, 146]. 

2 Bond and Thompson s Mechanism Unreduced Cold at the Interfiice 

In the mechanism proposed by Bond and Thompson [9] (Fig. 15.3), CO adsorbed on Au reacts with a hydroxy group located on a peripheral unreduced Au species, to form the carboxylate. The latter in turn reacts with a superoxide O2 ion formed on the oxide support like Haruta, the authors emphasise that the interaction between gold and the support is particularly important, since it dictates the nature of the interface at which the reaction takes place. The hypothesis of the presence 

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High activity in CO oxidation when gold particles are smaller than 5 nm, and supported on reducible oxides, such as iron oxide or titania, led Haruta et al. [3, 5-8] to propose the first mechanism of CO oxidation (Fig. 15.2) the reaction takes place at the interface between the gold metal particle and the oxide support, i.e., between CO adsorbed on the gold particles and O2 activated by the oxide support Later, based on the assumption that metal cations could be located at the metal-support interface. Bond and Thompson [9] proposed a mechanism rather similar. 

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