Fuel Desulfurization Performance Of Novel Carbon-based Composites Materials

The deep desulfurization of transportation fuels such as diesel,gasoline and jet fuels has attracted widespread attention due to the environmental pollution and poisoning of catalytic converters in vehicle exhaust causued by sulfur compounds in the fuel oil.Judging from the National VI vehicle fuel oil standard implemented nationwide in 2020,the sulfur content in gasoline and diesel cannot exceed 10ppm,which makes fuel oil desulfurization even more important.For fuel oil desulfurization methods,scientific research mainly focuses on hydrodesulfurization（HDS）,adsorption desulfurization（ADS）or oxidative desulfurization（ODS）.It is inevitable to mention the catalytic or adsorbent materials used in these desulfurization methods.Among various materials,novel carbon has broad application prospects in the fields of catalysis and adsorption due to its tunable surface chemistry and abundant pore structure,strong stability and low cost.Therefore,how to effectively modulate the structure and morphology of carbon materials to improve catalytic or adsorption performance still needs to be further explored,which is of great significance to meet the requirements of high efficiency,high selectivity and high stability for deep desulfurization.In this dissertation,a systematic study on the development of high-performance carbon-based catalytic and adsorption materials has been carried out,and some meaningful research results have been obtained as follows:（1）A strategy of modifying traditional hydrodesulfurization catalysts with heteroatom-doped carbon materials is proposed,which solves the problem of excessive interaction between active metals and supports.First,composite supports were prepared by modifyingγ-Al₂O₃ substrates with N and P co-containing precursors,and then Co and Mo were supported on various hybrid supports by isovolumetric impregnation and pyrolysis to synthesize high-efficiency HDS catalyst.Among them,N and P anchor the metal and appropriately weaken the acidity of the support during the high-temperature calcination process,while N and P provide electrons for the active metal.As a result,the resulting composite catalyst obtain a higher degree of sulfidation and thus generate a high-performance catalytic material.Thanks to the resulting highly active and uniformly dispersed metals,the as-prepared composites achieve high removal rates（99%）and high k _HDS values(5.12×10^-7 mol g^-1 s^-1)and a direct desulfurization pathway（DDS）with less hydrogen consumption.In addition,density functional theory（DFT）calculations confirmed that the electron-donating effect of N and P enhanced the dispersion of metallic Mo species,weakened the Mo-O/Mo-S bond,created more active sites.The composite catalyst exhibits much higher catalytic hydrogenation performance than similar materials.Subsequently,series of characterizations showed that heteroatoms have an effective regulation effect on the carbon matrix and even the whole catalyst.This provides an effective strategy for the rational design and efficient synthesis of efficient HDS catalysts for industrial applications.（2）A strategy to construct P,N co-doped hierarchical porous carbonaceous adsorbents by template method is proposed,which solves the problems of low sulfur capacity and poor selectivity caused by inappropriate surface chemistry and microstructure.Firstly,triphenylphosphine and 1,10-phenanthrophos were introduced as P and N sources,while magnesium oxide was used as a template to prepare P,N co-doped porous carbon materials by a simple calcination method.These porous carbons are composed of a large number of hexagonal sheet-like structures,which fully expose the active sites through the broad specific surface area.Through a series of analytical characterizations,it was found that the porous carbon prepared by this method has a micro-mesoporous structure.By examining its adsorption performance,it can be seen that the highest sulfur capacity is 63.32 mg/g,which can be used continuously for 6 times and has good selectivity for the removal of DBT.By analyzing its surface chemical properties and adsorption kinetics,it is known that the unique micro-mesoporous structure ensures the adsorption selectivity of DBT and accelerates adsorbate transport.More importantly,the abundantly formed N-P bonds act as adsorption active sites,which enhances the adsorption strength to DBT.The co-doped porous carbon indeed has a significant affinity for DBT,which is confirmed by density functional theory（DFT）calculations.This provides a certain reference for the design and preparation of efficient fuel oil ADS adsorbents.（3）A strategy to reconstruct transition metals as catalysts by modulating the morphology and loading mode is proposed,which solves the problems of poor dispersibility and stability of ODS catalysts.First,melamine and glucose were used as N and C sources to react with ferric chloride hydrothermally,which were then pyrolyzed under argon atmosphere and obtained a new NC-modified carbon nanoparticle at high temperature.N species in CNTs tune the oxidative ability of metallic Fe,while Fe catalyzes the generation of zero-valent iron nanoparticles encapsulated in N-CNTs.The catalyst with this unique structure excites highly active free radicals with the assistance of H₂O₂,while the N-doped carbon tube fully exposes a large number of defects,which has excellent electrical conductivity and material transport ability.The obtained catalyst exhibits outstanding catalytic performance（Within 120 min,the oxidative removal rate of DBT reached 96%）and enhanced stability.In addition,through extensive characterization analysis,it can be seen that the large specific surface area,unique two-dimensional tube channel and mesoporous structure of this catalyst promote the diffusion and transfer of reactants and electrons,which provide a high density of active sites and integrate adsorption and catalysis at the same time.After comprehensively investigating the effect of catalyst dosage,hydrogen peroxide dosage,reaction temperature and different sulfides on desulfurization efficiency,it is believed that this strategy will provide new ideas for the development of advanced nanomaterials for fuel oil desulfurization.