Cobalt species and cobalt-support interaction in glow discharge plasma-assisted Fischer-Tropsch catalysts

Cobalt species and cobalt-support interaction in glow discharge plasma-assisted Fischer-Tropsch catalysts were studied using a combination of characterization techniques (X-ray diffraction, thermo-gravimetric analysis, temperature-programmed reduction, in situ magnetic measurements and in situ X-ray absorption). The catalysts were prepared by incipient impregnation using solutions of cobalt nitrate and ruthenium nitrosyl nitrate followed by plasma or/and oxidative treatment. Cobalt dispersion in silica-supported catalysts was significantly enhanced by plasma pretreatment. Cobalt particle size was a function of glow discharge plasma intensity. The concentration of cobalt silicate in plasma-assisted samples was low. No noticeable effect of the plasma pretreatment on the formation of barely reducible cobalt silicate species was observed. Cobalt reducibility was to some extent hindered in the plasma-assisted catalysts, while promotion with ruthenium significantly enhanced cobalt reducibility in silica-supported catalysts. Due to the combination of high cobalt dispersion and optimized cobalt reducibility, ruthenium-promoted plasma-assisted cobalt catalyst exhibited an enhanced activity in Fischer-Tropsch synthesis. (C) 2010 Elsevier Inc. All rights reserved.