Preparation And Characterization Of Ruthenium Based Catalysts For Fischer-Tropsch Synthesis

Fischer-Tropsch?FT?synthesis is a chemical process producing liquid fuels or other high value products with synthesis gas?CO and H₂?.Catalyst is essential for the performance of FT synthesis,especially having effects on the CO/H₂ conversion and product selectivity.In this work,active carbon?AC?was selected as support to prepare Ruthenium FT catalysts.Two methods,i.e.impregnation-calcination and impregnation-hydrazine hydrate reduction methods were applied.Properties of the secured catalysts or their precursors were characterized by BET,X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscopy?TEM?,temperature-programmed reduction?H₂-TPR?,temperature-programmed desorption?H₂-TPD?and X-ray photoelectron spectroscopy?XPS?.Catalytic performances of the part of the catalysts were estimated via testing the CO conversion during FT synthesis.By impregnation-calcination method,Co/AC and Ru/AC¹ catalysts were prepared.It was shown that specific surface areas,pore volumes of the samples decrease with the increasing metal loading amount.After calcination process,the loaded Co and Ru on AC carrier were partly reduced to metal states;while for the Ru/AC¹ samples with high Ru content?>10 wt%?,most of the loaded Ru is of metal state,which is confirmed by the results of XRD,H₂-TPR and XPS.The increase of Ru content could lead to the increase of Ru particle size and decrease of its surface dispersity,due to the migration and growing of Ru particles during calcination.15 wt%Ru/AC¹ was found to possess lower H₂ adsorption capacity than 15 wt%Co/AC,which have smaller metal particles and higher surface dispersity.Applying impregnation-hydrazine hydrate reduction method,a series of Ru/AC²catalysts were prepared.XPS results indicated that hydrazine hydrate could reduce the Ru of Ru/AC precursor obtained via impregnation process to metal state.The mild reduction condition at 80 ^oC leads to the smaller Ru particles and higher specific surface areas than those of Ru/AC¹,especially for 15 wt%Ru/AC¹ and 15wt%Ru/AC².It was also proved by H₂-TPD that Ru/AC² has higher H₂ adsorption capacity than Ru/AC¹.All above properties will benefit the performance of Ru/AC² in FT synthesis.CO conversion was tested during FT synthesis experiments to estimate the activities of the catalysts.As for Co/AC catalysts,CO conversion increases obviously with the increasing Co content.Both Ru/AC¹ and Ru/AC² showed higher activities than Co/AC,while Ru/AC² possesses the highest activity among all the tested samples.It suggested that Ru has excellent catalytic properties for FT synthesis.On the other hand,with the mild preparing condition of impregnation-hydrazine hydrate reduction method,Ru/AC²could be secured with high specific surface area and high dispersity,and consequently high activity.