Study On The Construction,property Control And Hydrodenitrification Performance Of Carbide Catalysts

Under the goal of carbon neutrality,the efficient and clean use of renewable biomass energy is gaining more and more attention,among which the third generation biofuel"microalgae biofuel"is attracting attention as a carbon neutral feedstock because it can avoid the competition with food crops for arable land.However,microalgae biofuels contain a large amount of nitrogenous compounds,the presence of which leads to the generation of pollutant NO_xduring the combustion process and catalyst poisoning during the subsequent biocrude reforming process,making hydrodenitrogenation（HDN）a necessary process in bio-oil production.However,conventional hydrodenitrogenation focuses more on the ability of the catalyst to remove nitrogen atoms from the oil,while the selectivity of hydrogen depletion and other high value chemicals such as aromatic products is often neglected.In this paper,different series of molybdenum carbide catalysts were prepared using biomass as feedstock,and the properties and structures of various molybdenum carbides were investigated using XRD,XPS,BET,H₂-TPR,SEM,HRTEM,ICP-OES,Raman spectroscopy and elemental analysis.Moreover,HDN reaction studies were carried out using quinoline as a model compound to examine the effect of reaction conditions and then combined with density flooding theory（DFT）calculations to reveal the mechanism of quinoline hydrodenitrogenation reaction.The main research contents include:（1）The effects of pretreatment atmosphere（N₂,H₂,NH₃）,and biomass feedstock（soybean straw,sorghum straw,and cotton straw）on the catalysts of molybdenatment atmosphere significantly affects the crystalline structure of Mo in the molybdenum-based biomass carbon material catalysts,with N₂ causing some of the MoO₂ to be insufficiently carbonized and H₂promoting the reduction of some of the MoO₂ to Mo monomers because of the strong reducing properties.A carbothermal ammonia reduction method was used to prepare biomass char-loaded molybdenum carbide catalysts,i.e.NH₃ and straw were used as nitrogen and carbon sources,respectively,to form nitrogen-doped biomass char materials,and molybdenum carbide was formed in situ on the biomass char.Compared with pureβ-Mo₂C,the introduction of nitrogen-doped carbon carrier significantly changed the specific surface area and electronic properties of molybdenum carbide,and effectively enhanced the quinoline HDN performance.Compared with sorghum straw and cotton straw,soybean straw contains sufficient carbonaceous compounds to generate pure-phaseβ-Mo₂C.（2）The effects of carbonization gas velocity（100 m L/min,150 m L/min,200 m L/min）and carbonization end temperature（600°C,700°C,800°C,900°C）on molybdenum carbide on biomass charcoal were investigated.Too large gas velocity（>100 m L/min）will lead to excessive generation ofγ-Mo C in the reducing material,too low carbonization end temperature（600°C）will lead toβ-Mo₂C not forming,and too high carbonization end temperature（900°C）will lead to sintering and carbon accumulation on the catalyst surface.molybdenum carbide（β-Mo₂C/NBC）formed by carbonization at 700°C in HN₃ atmosphere at 100 m L/min,has the the best quinoline HDN effect with 99%quinoline conversion and denitration,while the selectivity to aromatic products can reach 89.1%.Compared withβ-Mo₂C,the selectivity of aromatic products increased by 51.3%.The stability ofβ-Mo₂C/NBC catalyst was also investigated,and there was no significant change in catalyst activity and good stability during the continuous reaction time of 110 hours.（3）Construction of mesoporous biomass carbon loaded with molybdenum carbide（β/NBC@NC）using graphitic phase carbon nitride（g-C₃N₄）as a templating agent.The percentage of Mo²⁺（i.e.,β-Mo₂C）and the amount of active nitrogen on the modified catalyst surface were significantly increased and the average catalyst particle size was reduced,especially significantly reducing the difficulty of oxide removal from the molybdenum carbide surface so that it could be largely completely removed at the reaction temperature of 380°C.However,the use of more g-C₃N₄ for modification would make the precursor insufficiently carbonized and generate heterogeneous MoO₂.The catalyst performance was enhanced with the increase of reaction temperature.During the experiments,the catalyst performance was enhanced with increasing reaction temperature.Under the action ofβ/NBC@NC-1.0 and suitable reaction conditions(T=400℃,P=4.0 MPa,LHSV=18 h^-1,H₂/Oil=500),the conversion and denitration of quinoline were greater than 99%,the aromatic product selectivity was improved to 95.6%,and the processing capacity（liquid-time air velocity）of the feedstock was increased by about 50%.（4）Different reaction conditions significantly affected the performance ofβ-Mo₂C/NBC-catalyzed quinoline hydrodenitrogenation reaction.The higher the reaction temperature,the better the performance of theβ-Mo₂C/NBC catalyst in the HDN reaction;too low liquid-time air velocity will partially saturate the aromatics in the products with hydrogenation,while too high liquid-time air velocity will make the quinoline reaction incomplete.The hydrogenation reactions of THQ1,THQ5 and propylbenzene were supplemented,and it was resolved that the aromatic products in the products mainly came from THQ1,and the saturated products mainly came from THQ5,and they could be converted to each other;the conversion ability ofβ-Mo₂C/NBC to propylbenzene was poor（≤6.1%）,and the EB,MB and B in the products were mainly generated from OPA and PCHA by breaking the C-N and C-C bonds simultaneously,and only a small portion was generated from PB by breaking the C-C bond step by step.（5）The adsorption energy data on the pure phaseβ-Mo₂C（101）,nitrogen-doped carbon loadedβ-Mo₂C（101）/NBC surface were combined with density flooding theory（DFT）calculations,and the adsorption energy of the reactant quinoline molecules on the catalyst surface was higher than that of the product molecules by analysis,and the adsorption energy of the loaded molybdenum carbide was significantly larger than that of the molybdenum carbide without a carrier.The mechanism of hydrodenitrogenation of quinoline overβ-Mo₂C/NBC and the reason for the higher selectivity of aromatic products are described.In addition,the surface adsorption energy calculations ofβ-Mo₂C（001）/NBC andα-Mo C_1-x（111）/NBC of different crystalline phases are supplemented,and the speculation thatα-Mo C_1-x（111）/NBC may tend to generate saturated products is proposed.