Regeneration of model supported metal catalysts

Abstract

Regeneration of a model catalyst of Pt over γ-Al 2O 3 was studied as a function of time using a TEM. The decrease in particle diameter was accomplished by heating the sample in air at 500 °C for times up to 2 h. The results were analyzed using a model which is shown to be particularly valid for short times and large particle sizes. The model postulates a surface layer of oxide on the supported metal particle. The difference between PtPt distances in the surface layer of platinum oxide and in the unoxidized metal gives rise to forces which may crack and split the particle. The experimental results indicate that the initial regeneration rate is rapid, and that the rate falls off after about 2 h of heating. Applying the model to the experimental data yields values for an average rate of oxidation of 2.37 nm/h, and a minimum particle diameter for crack initiation of 8.6 nm. These values are consistent with numbers obtained for these parameters from completely different circumstances.