EFFECTS OF SODIUM ON THE STRUCTURE AND FISCHER-TROPSCH SYNTHESIS ACTIVITY OF RU/TIO2

The influence of Na on the migration of Ti-containing moieties onto the surface of Ru particles supported on titania has been investigated, together with the effects of Na on the activity and selectivity of titania-supported Ru for Fischer-Tropsh synthesis. It is demonstrated that Na facilitates the decoration and partial encapsulation of Ru by Ti-containing moieties as a consequence of the formation of sodium titanates. Since the Tammann temperature of the titanates is lower than that of the anatase or rutile phases of titania, the temperature at which Ti-containing moieties begin to migrate is reduced in the presence of Na. The turnover frequency for CO consumption based on exposed Ru sites is observed to be independent of the Na content of the catalyst, but the turnover frequency for methane formation decreases monotonically with increasing Na content. The probability for chain growth and the olefin-to-paraffin ratio increase and the extent of ethylene reincorporation into the reaction products decrease with increasing Na content. These effects are attributed to a reduction in the surface concentration and mobility of H atoms adsorbed on Ru. (C) 1995 Academic Press, Inc.