Propene epoxidation catalyst deactivation

The rate of catalyst deactivation is a function of the TS-1 crystal size [12a, 13a] with larger crystals, the slow diffusion of the epoxide solvolysis products (especially with more hindered products) makes the blockage of pores more likely. In propene epoxidation, polyethers are mainly responsible for this phenomenon, when the catalyst is used in consecutive reaction cycles. The activity of the catalyst can be restored by washing it with a solvent or by calcining it at temperatures higher than 500 °C. 

FIGURE 12.6 Deactivation versus the amount of propene oxide produced during the propene epoxidation over 1 wt.% Au/Ti02. 0 propene oxide formation rate A water formation rate/10. [0.3 g of catalyst, 50 Nml/min gas feedrate (10% H2, O2, and propene), total pressure 1.1 bar(a).]... 

T. A. Nijhuis, T. Q. Gardner, B. M. Weckhuysen, Modeling of kinetics and deactivation in the direct epoxidation of propene over gold-titania catalysts, /. Catal. 236 (2005) 153. 

The link between the deactivation and the epoxidation is made clear in Fig. 12.5, in which the hydrogen oxidation reaction (no propene) is observed to be stable for 25 h. Once propene is added to the feed thereafter, the catalyst starts deactivating rapidly. Removal of the propene in the feed stops the deactivation process and the catalytic activity gradually increases. The fact that even after 25 h, the activity is not back to its original level, indicates that the deactivating species are bonded strongly to the catalyst. 

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