Study On The Reaction Performance Of Ruthenium Based Catalysts Supported On Carbon For Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis(FTS)is a key technology for conversion of synthesis gas.It can convert carbon from various non-petroleum carbon resources such as natural gas,coal and biomass into clean hydrocarbon fuels as well as valuable chemicals,which is an effective way to achieve green energy.The current research on Fischer-Tropsch synthesis focuses on the development of catalysts,the exploration of reaction mechanism and the design of reactors.The performance of the catalyst directly determines the efficiency of Fischer-Tropsch synthesis.Therefore,the development of new Fischer-Tropsch catalysts has become a hot research.In this thesis,a series of ruthenium-based Fischer-Tropsch catalysts were prepared by impregnation with graphite(G)and expanded graphite(EG)as supports.The structure and phase of the catalysts were characterized by X-ray diffraction(XRD),X-ray fluorescence(XRF),temperature-programmed reduction(H₂-TPR),X-ray photoelectron spectroscopy(XPS)and nitrogen adsorption-desorption.In addition,Fischer-Tropsch synthesis experiments were performed on a fixed bed reactor.The work and conclusions of this thesis are as follows:The Ru/EG catalysts were prepared by the incipient wetness impregnation method with EG as the support,and the effects of reduction temperature(200,250,300,400°C)on the catalytic performance were investigated.The experiments showed that the reduction temperature affected the size of Ru particles.Higher reduction temperature caused larger Ru particles.When the reduction temperature was 400°C,Ru particles might agglomerate and sinter,resulting in an excessively large Ru particle size,and most of the Ru particles could not enter the interior of the pores,which limited its catalytic effect and deactivated the catalyst.When the reduction temperature was 200°C,the temperature did not reached the temperature at which the reduction peak was located according to the results of H₂-TPR,so Ru could not be completely reduced at 200°C,resulting in a lower CO conversion.When the reduction temperature reached to 250°C or 300°C,the Ru particles were completely reduced,and the particle size of Ru was smaller and the dispersibility was better at 250°C.The highest CO conversion rate and C₅₊selectivity were achieved at 250°C,thus,250°C was the optimal reduction temperature for Ru/EG.A series of Ru/G catalysts were prepared using different size of graphite such as 325mesh,1000 mesh and 3500 mesh via over-impregnation method.The effect of particle size of support was studied.The results showed that the Ru/G₃₅₀₀ catalyst exhibited the best activity and product selectivity.The activity of Ru/G₁₀₀₀ and Ru/G₃₂₅ and the selectivity of C₅₊were lower than that of the Ru/G₃₅₀₀ catalyst,which was believed to be caused by the formation of Ru particles with different particle sizes.However,the Ru/G₃₅₀₀ catalyst was unstable and the activity decreased significantly during a short time.It might due to the over-fine particle size of this support,which led to the decrease of the interaction between Ru and graphite,and the easy desorption of Ru in the reaction process.In general,it was believed that Ru/G₁₀₀₀ was the catalyst with the best performance for Fischer-Tropsch synthesis among the three catalysts.Comparing the performance of Ru/EG and Ru/G₁₀₀₀ catalysts,it was found that the activity of the Ru/G₁₀₀₀ catalyst was higher,and the C₅₊selectivity of the Ru/EG catalyst was better.It was believed that the pore size of 1000 mesh graphite was larger,which facilitated the diffusion of the reactant molecules and the product molecules in and out of the pores.However,when the conversion rate of Fischer-Tropsch synthesis was low,the hydrogenation ability of the active metal was weak and the chain growth ability was strong,which was more conducive to produce long-chain hydrocarbons.Therefore,the C₅₊selectivity of Ru/EG catalyst was higher and the CH₄ selectivity was lower.