Platinum ions particle size effects

The surface crystal structure and particle size can also influence photoelectro-chemical activity. The mode of pretreatment, for example, dictates whether titanium dioxide exists in the anatase phase (as is likely in samples which have been calcined at temperatures below 500 °C) or in the rutile phase (from calcination temperatures above 600 °C) or as a mixture of the two phases for pretreatments at intermediate temperature ranges. The effect of crystalline phase could be easily demonstrated in the photocatalytic oxidation of 2-propanol and reduction of silver sulfate, where anatase is active for both systems. But when the catalyst was partially covered with platinum black, alcohol oxidation was easy, but silver ion reduction was suppressed. On rutile, redox activity was observed for Ag+, alcohol oxidation was negligible [85]. 

Nevertheless, it is necessary to return to the main point of interest here, which is the effect of deactivat ion and the accumulation of carbonaceous species on the Pt surface on the structure sensitivity or insensitivity exhibited (as inferred from the dependence of K on the platinum surface area)- Turnover numbers so calculated after 10 min reaction time decrease rapidly with increasing platinum surface area in a hyperbolic manner (and increase almost linearly with the mean platinum particle size) for reactions followed at both 3L3K and 295K, in contrast to the results obtained by Boudart over a narrower range of Pt surface area, Such behaviour very unusual but has been reported for structure sensitivity in cyclopentadiene hydrogenation on supported copper. However, the turnover numhers were almost independent of platinum surface area and... 

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