Co- and Co(Ru)-Based Catalysts for Fischer-Tropsch Synthesis Prepared by High Power Ultrasound

摘要

Fischer Tropsch (FT) is an industrial process that converts syngas (H_2 + CO), using iron or cobalt based-catalysts, in hydrocarbons in the range C_1 to C_(100). Cobalt-based catalysts have been used for FT for long time due to their long life-times, high CO conversion and high selectivity to heavy hydrocarbons; moreover they are characterized by low water gas shift activity, so avoiding the CO_2 formation. The use of ultrasound in material chemistry is a very interesting technique to prepare novel supported materials with particular properties as nanostructured catalysts. The catalysts were prepared by a modified impregnation method. The metal precursors (cobalt and ruthenium carbonyl) were dissolved in n-decane together with the different support (SiO_2, Al_2O_3 or TiO_2) and irradiated by an US horn. After precipitation of metal nanoclusters on supports, the catalysts were dried and calcinated. All the catalyst were characterized by BET, TPR, FE-SEM, TEM, micro-Raman and XRD analysis. Tests in a pilot laboratory-scale plant have evidenced the peculiar quality of synthetic procedures and suggested new strategies for improving the efficiency of catalytic compounds. The catalysts show a low selectivity to methane and carbon dioxide and formation of higher hydrocarbons. The more interesting results are the highest CO conversion, at lower temperatures, obtained with Ru-promoted catalysts.