The solvated metal atom impregnation (SMAI) method was used to prepare Co/SiO 2 and Co/La SiO 2 catalyst samples with 5%Co content. The XPS results showed that the cobalt particles both in SiO 2 and in La SiO 2 existed in zero valent state (Co\+0). The CO chemisorption results showed that the cobalt particle size (5 3 nm) of Co/La SiO 2 sample was much smaller than that (8 1 nm) of Co/SiO 2 sample. The turnover frequency (TOF) of CO on Co/La SiO 2 sample was higher than that on Co/SiO 2 sample in F T reaction (CO hydrogenation), which was probably due to the fact that the cobalt particle size in Co/La SiO 2 sample was much smaller than that in Co/SiO 2 sample. The experimental results also showed that the selectivity of Co/La SiO 2 sample for long chain paraffins was higher than that of Co/SiO 2 sample.
