Modulations On Metal-support Interactions Of Ruthenium-based Catalysts For Fischertropsch Synthesis

Fischer-Tropsch synthesis（FTS）could convert synthesis gas（carbon monoxide and hydrogen）to liquid fuels and other high value-added chemicals.It is an effective way to realize clean and efficient valorization of non-petroleum carbon resources.The rapid development of FTS technology can alleviate the contradiction between petroleum supply and demand,providing guarantee for the national energy security.Although this technology has been commercialized,there are still many scientific questions related to the catalyst design and mechanism research,in which the biggest challenge is the selective control of products.Affected by the Anderson-Schulz-Flory distribution,the products in FTS are widely distributed.The selectivity to high value-added products such as liquid fuels is very low,which severely restricts the efficient conversion and utilization of syngas.In this reaction,supported Ru-based catalysts are widely studied due to their excellent activity,enhanced chain growth ability and high stability.Through the systematic analysis of the geometric and electronic structure,as well as the physical and chemical properties of the catalyst,we can not only provide deep molecular insights into the subsequent design of the catalyst,but also clarify the structure-performance relationship by linking to the Fischer-Tropsch synthesis performance,which is conducive to in-depth understanding of the reaction mechanism of the catalyst in the reaction and further promote the rational design of efficient catalysts.To control both geometric and electronic structures of active sites in catalysts with metal-support interactions,TiO₂ and graphene-based carbon materials were used as the supports for the construction of Ru-based catalysts.Detailed analysis of structure-performance relationship was demonstrated in this thesis.The main research work are as follows:（1）The TiO₂-supported catalyst is prone to produce strong metal-support interactions during the reduction process,causing the inevitable migration from the partially reduced suboxide species（TiO_x）to the metal surface.This phenomenon will decrease the number of exposed active sites on the metal surface and decrease the catalytic activity.To solve this problem,the dopamine sacrificial coating strategy was proposed to prepare the Ru/TiO₂ catalyst.Systemically experiments revealed that this strategy not only effectively inhibits the coating of the metal by the TiO_x layer during the reduction process,but also can controllably adjust the ratio of the metal surface-exposed sites and interficial sites.The two active sites were analyzed in detail by in-situ high-pressure in-situ Diffuse Reflectance Fourier Transform infrared spectroscopy（DRIFTS）and other advanced characterization methods,and it was found that the intrinsic activity（TOF）of the metal surface-exposed sites was 5.3 times that of the interficial sites.The former sites also had stronger chain growth ability and thermal stability.（2）To strength the chemical bond between metal and adsorbed C species,and further increase the selectivity of heavier hydrocarbons,we conducted different pretreatment strategies on the modulation of defects distribution and concentration in the TiO₂ material.This method effectively tuned the electron transfer behavior under the metal-support interaction,and the result proved that the bulk Ti³⁺species could induce the electron transfer from the support to the metal.This interaction increased the charge density on Ru and hence strengthen the metal-C bond.Therefore,C-C coupling reaction was promoted significantly,which is also conducive to the production of heavier hydrocarbons.（3）To overcome the inherent shortcomings of traditional carbon materials including the poor mechanical strength and the difficulty in catalyst shaping,the 3D graphene-based carbon materials were investigated as catalyst supports and the resemble-assembly method was combined to construct Ru-based catalysts.Detailed studies elucidated that different assemble methods will affect the dense structure and surface defect content of the catalyst.Among them,the carbon material prepared by the hydrothermal method had compact structure,enhanced graphitization degree and metal-support interaction,hance exhibited excellent stability in the FTS.However,the adsorption of H species on HPGM-based catalysts is favorable and hence it displays high CH₄selectivity.In contrast,the structure of carbon material prepared by the chemical reduction method was less compact and exhibited weaker metal-support interactions,which can inhibit the adsorption of H species and decrease the CH₄selectivity.