Abstract

LOAIZA-GIL, A et al. CHARACTERIZATION OF ULTRA FINE SILICA SUPPORTED IRON CATALYSTS PREPARED BY THE AMMONIA METHOD. Rev. LatinAm. Met. Mat. [online]. 2002, vol.22, n.1, pp.47-51. ISSN 0255-6952.

New ultra fine particle size and nonporous Fe/SiO2 catalysts ranging 20-160 nm were prepared with a modified high loading ammonia method. Scanning electron microscopy (SEM) associate to x-ray energy dispersion spectroscopy and nitrogen fisisorption studies of the fresh catalysts dried at 353 K shows a non porous structure constituted by superimposed sheet of rectangular crystals of Phyllosilicate type. The chemical and structural composition of such solids changes with the thermal pretreatment under hydrogen flow. FT-IR studies performed at programmed reduction temperature suggests that the fresh catalyst is constituted by an iron complex like Fe(H₂O)₆⁺³ sandwiched between bi-dimensional sheets of Si₂O₅ phyllosilicate. The amount of -OH groups bonded to the iron complex and those associates to the Si₂O₅ polymeric groups decrease progressively to disappears by slowly heating at 1 K/min from 353 to 973 K under hydrogen flow. At the final reduction temperature, a new catalyst structure constituted by silica support finely dispersed iron crystallites arise suggesting a catalyst morphology and properties governed by the temperature.

Keywords : Catalyst; Iron; ammonia method; Fischer Tropsch.