VINYLIC INITIATION OF THE FISCHER-TROPSCH REACTION OVER RUTHENIUM ON SILICA CATALYSTS

Vinylic probes were added to a ruthenium-catalysed Fischer-Tropsch rea ction in order to study the mechanism of hydrocarbon formation from CO /H-2. C-13(2) units derived from (CH2)-C-13=(CHBr)-C-13 or (CH2)-C-13= (CH2)-C-13 are readily incorporated into the alkene and alkane product s formed from (CO)-C-12 and H-2 over a Ru/SiO2 catalyst (1 atm, 180 de grees C). The levels of C-13(2) incorporation suggest that the probes are sources of C-13(2)-labelled initiating units, proposed to be surfa ce vinyls (-CH=CH2). Further evidence for vinyl initiation is given by the increase in hydrocarbon formation rate during vinylic probe addit ion. This rate increase is not observed when ethyl bromide is added as a probe and shows the significance of the unsaturated initiating unit . C-13(4) incorporation in the C-4 hydrocarbon products (especially ci s-2-butene) is attributed to a facile vinyl dimerisation reaction, as previously observed on rhodium catalysts and in discrete organometalli c complexes. Hydrogenolysis of the C-13(2)-probes was an appreciable s ide reaction over Ru/SiO2 and resulted in some incorporation of C-13(1 ) units. (C) 1997 Academic Press.