STUDY OF THE DEACTIVATION MECHANISM OF AL2O3-SUPPORTED COBALT FISCHER-TROPSCH CATALYSTS

The influence of water on alumina-supported cobalt catalysts has been studied. The deactivation of supported Co catalysts was studied in a f ixed-bed reactor using synthesis gas feeds containing different concen trations of water vapour. Supporting model studies were carried out us ing H2O/H-2 feeds in conjunction with XPS and gravimetry. Rapid deacti vation occurs on Re-promoted Co/Al2O3 catalysts when H-2/CO/H2O feeds are used, whereas unpromoted Co/Al2O3 shows more stable activity. The results from the gravimetric studies suggest that only a small fractio n of the bulk cobalt metal initially present reoxidizes to cobalt oxid e during reaction. However, the XPS results indicate significant reoxi dation of surface cobalt atoms or highly dispersed cobalt phases, whic h is likely to be the cause of the observed deactivation. Rhenium is s hown to have a marked effect on the extent of reoxidation of alumina-s upported cobalt catalysts.