Unlike the iron catalyzed Fischer-Tropsch (FT) synthesis, the additions of ethanol-d(6) and 2-propanol-d(8) during the Co/SiO2 catalyzed FT reactions did not produce detectable amount of deuterated isomer in any alkane. However, when the FT reactions were conducted over a mixture of FT catalyst Co/SiO2 and dehydration catalyst Al2O3. the d(1), d(2) and d(3) isomers of alkanes from C-7 to C-15 were obtained with a nearly constant D/molecule value of 1.4 when ethanol-d(6) was used as the tracer while d(1)-d(6) isotopic isomers of alkanes were observed with a nearly constant D/molecule value of 2.3 when 2-propanol-d(8) was used. The similar results were obtained when 1-propanol was used as the tracer. These results lead us to conclude that the C-2 or C-3 species that initiates the chain growth in the FT reaction resembles ethene or propene. The pathways for the formations of ethylidene and propylidene were proposed. (C) 2011 Elsevier B.V. All rights reserved.