THE ROLE OF ALKALI PROMOTERS IN FISCHER-TROPSCH SYNTHESIS ON RU SIO2 SURFACES/

Cs-promoted Ru-Na/SiO2 catalysts were characterized via H-1 NMR spectr oscopy. Contrary to the results of studies using single crystals, we d id not find any evidence of a ruthenium-mediated electronic interactio n between the alkali promoter and adsorbed hydrogen. The site blocking effects of the Cs promoter diminished after exposure to hydrogen for extended periods of times. This effect was partly reversible after the rmal evacuation of the hydrogen. In the presence of Cs, the surface of the support was also modified; the intensity of the diamagnetic reson ance in the spectrum (predominantly Si-OH) decreased, and an additiona l resonance appeared in the spectra. There is evidence that hydrogen s pillover and hydrogen mobility were also restricted in the Na-Cs-promo ted system.