The iron loading of catalysts, supported on SiO2, was investigated between 10 and 75 wt%, with and without the addition of promoters (K and Cu), in order to highlight the different catalytic performances of the samples in the Fischer-Tropsch synthesis. An optimization study of the prepared catalysts (active metal/promoters ratio, catalysts' activation procedure before the Fischer-Tropsch runs, influence of the feeding gas composition) is reported. The mechanical resistance of the catalysts was also evaluated using a suitable method involving ultrasound.