Platinum catalysts ostwald ripening

Agglomeration of Pt crystallites due to Brownian motion can really be observed and it can also be shown that, indeed, the interaction between the Pt particles and the supporting soot in the presence of the electrolyte, phosphoric acid, is weak enough to allow for relatively free movement of the Pt particles. This fast process obviously is also the reason for the nonobservability of slower surface diffusion-induced Ostwald ripening. Fortunately alloy catalysts composed of platinum and nonnoble metals seem to show a reduced tendency to agglomeration as their deterioration and activity loss is much slower than that of the pure platinum catalyst. 

For a sufficiently reducing reactant like ethanol both reversible and irreversible deactivation can be neglected. For MGP however unable to keep the catalyst in a low oxidation state particle growth occurs most probably via an Ostwald-ripening mechanism resulting in an irreversible decrease of the platinum surface area exposed. 

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