Co and Co-Ru based catalysts prepared by high power ultrasound for the Fischer-Tropsch synthesis

For political and environmental concerns posed by the still large exploitation of fossil fuels, it is imperative to develop economical and energy-efficient processes for the sustainable production of alternative fuels and chemicals. Fischer Tropsch synthesis (FT) is a well-established industrial process whereby these objectives can be achieved by using syngas (mixture of H2 and CO), manufactured from CH4, coal or, as a new tendency, from biomass. FT is an industrial process that converts syngas using iron or cobalt based-catalysts, in hydrocarbons in the range C1 to C100. The major products of FT process are comprised of hydrocarbon fuels (such as gasoline, diesel fuel and jet fuel), olefins, waxes, and oxygenated compounds (such as alcohols). Both catalyst specifications and operating conditions govern the composition of the products [1]. 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 CO2 formation. The use of ultrasound in material chemistry is a very interesting technique to prepare novel supported materials with particular properties as nanostructured catalysts [2]. The chemical effect of US arises from acoustic cavitation, i.e. the formation, growth and implosive collapse of bubbles in a liquid. Some of the interesting features resulting from the application of sonication as a synthetic method are the nanoparticles preparation, showing a more uniform size distribution, higher surface area and a more controlled phase composition. The main parameters for US application are the emitted power in solution, the frequency and the sonication length. The use of high power ultrasound for long time is a difficult procedure because it is a critical point the control of the thermal stability of the US horn. In this paper the possibility to use an ultrasound assisted synthesis of Co-based catalysts (Co or Co- Ru supported on silica, alumina and titania) by high power US for a long time has been investigated using an innovative experimental apparatus equipped with a new cooling system able to maintain stable the temperature US emitting horn.