Activity of Iron Hydroxide

During the course of studying the effect of crystallite sizes, attempts were made to produce very small unsupported iron oxide powders by lowering the calcination temperature of the iron hydroxyl gel that was precipitated from iron nitrate with ammonium hydroxide. However, catalysts calcined below 300°C still contain hydroxide, and they show high selectivity in butadiene production. For this reason, two catalysts, calcined at 250°C and 300°C, respectively, were studied in more detail. 

The magnetization curves of these samples are shown in Fig. 12. Characteristic of the hydroxide is the sigmoidal shape of the curves. This shape is retained in the 250°C calcined sample, but has almost disappeared for the 300°C sample. 

When the 250°C calcined sample was tested for the butene oxidation reaction at 250°C, butadiene was produced very selectively ( 80%). The selectivity decreases from about 90% initially to 80% after 12 hr of reaction (Fig. 13). The initial activity is high, but decreases rapidly in the first 2 hr. Regeneration of a catalyst after 13 hr of use by 02 at 250°C recovers the selectivity, but only half of the initial activity. Specific magnetization of the deactivated sample is lower than for a fresh sample, but the shapes of the magnetization curves are the same. 

Similar behavior was observed for the 300°C calcined sample. The initial activity and selectivity at 300°C are high (Fig. 14). The activity decreases 

These results show that iron hydroxide, although thermally not very stable, is a very active and selective catalyst for butene oxidation. It will be interesting if the thermal stability can be improved such that high conversions can be achieved with high selectivity. 

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