A gas-expanded-liquid technique (GXL) was applied to the preparation of supported iron catalysts for Fischer-T Ttopsch synthesis (FTS). A mixture of presynthesized iron oxide nanoparticles with an average size of 12 nm was deposit41 onto a SiO2 support in a manner such that nanoparticles smaller than S nm were excluded from the final catalyst product. A series Of SiO2-supported iron oxide nanoparticle catalysts were prepared with iron loadings of 11.4, 18.0, 24.0, and 28.8 wt %. Catalysts were characterized by nitrogen adsorption, inductively coupled plasma optical emission spectrometry, H-2 temperature programmed reduction (H-2-TPR), X-ray diffraction (XRD), trasmission electron microsopy (TEM), X-ray photoelectron spectroscopy, and carbon monoxide temperature-programmed desorption. TEM analysis showed that iron oxide naribparticleswere well-distributed over the surface of the SiO2 support with an increase in the iron loading resulting, in the formation of rnultilay&s and three-dimensional island's of iron oxide nanoparticles. H-2-TPR indicated that the reducibility_ of the iron oxide;nariopartides increased monotonically with iron loading. According to XRD results, the increase in the iron loading resulted in an :increase in the iron oxide crystallite size, and iron carbides were present in the used catalysts after solvent treatment. FTS was;carried out in a fixed -bed reactor at reaction conditions of 230 degrees C, 2 MPa, H-2/C0 = 1.70, and GHSV = 3000 L/kg(cat)/h. For the catalysts studied, the highest syngas conversion and iron time yield were observed at intermediate (18, 24 wt %) iron loadings. The C5+ selectivity and carbon chain growth probability factor were approximately 68% and 0.76, respectively, for each catalyst. A 16 wt % iron on SiO2 catalyst prepared by the same GXL technique was promoted with 0.7 wt % potassium using the incipient wetness method. As expected; K promotion resulted in a slight decrease in FTS activity and increased selectivity towara,CO2,ank C5+ selectivity.