Preparation And Performance Study Of Molybdenum-based Catalysts For Hydrodesulfurization

China's energy structure is rich in coal,poor in oil,and low in gas.Coal accounts for a large proportion of China's energy consumption,but the problems of low efficiency and environmental pollution for coal utilization were involved and need to be resolved.Developing the coal-to-fuel technology is a clean and efficient way to use coal resource.Hydrodesulfurization(HDS)is one of the most efficient processes for desulfurization,in which the catalyst is a key factor affecting the efficiency of desulfurization.The development of highly active and selective HDS catalysts is of great significance to rapidly develop coal-to-fuel technology and efficiently utilize our country's coal.This paper focuses on molybdenum-based HDS catalysts as the main research object.First,a series of MoS₂ catalysts were prepared by a solvothermal method,and the effects of anhydrous oxalic acid and ethanol on the structure and performance of MoS₂were studied.The results showed that the introduction of anhydrous oxalic acid and ethanol can enhance the catalytic activity of MoS₂.The catalysts regulated by ethanol and anhydrous oxalic acid possessed a high proportion of 1T phase MoS₂and abundant defected sites,thus providing a large number of active sites.Thus,excellent catalytic activity and high indirect desulfurization selectivity in the HDS reaction have been achieved using dibenzothiophene as a model compound.And then the preparation conditions of the MoS₂ catalyst,including crystallization time,oxalic acid dosage and ethanol amount,were studied through a series of comparative experiments.Then,the suitable conditions for the preparation of the catalyst were determined.Furthermore,using sublimation sulfur as the sulfur source,the chemical vapor deposition(CVD)method was employed to perform the treatment of secondary sulfuration on the MoS₂ prepared by the aforementioned solvothermal method.After secondary sulfuration,the crystallinity of MoS₂was increased,and the ratio of 1T phase was reduced.Meanwhile,the number of stacked layers and the size of the slab were significantly reduced,and more active sites could be exposed.Therefore,the as-prepared catalyst exhibited excellent catalytic activity.Then,the effect of temperature on the catalytic performance during the secondary sulfuration was determined.Different 1T proportions and defect concentrations have been obtained under different temperatures.The higher the treatment temperature,the more seriously the catalyst aggregated.MoS₂-400 showed the highest catalytic activity.Finally,the effects of the amount of sublimation sulfur and the retention time on the activity of the catalyst was systematically investigated.500 mg of sublimation sulfur and 200 min of the retention time were determined as the suitable conditions for catalyst preparation.Finally,supported Mo-based catalysts have been prepared and used in HDS reaction.Using SBA-15 as the support,a series of catalysts were prepared by the impregnation method.The influences of the impregnation sequence and the structure of S source on the catalytic performance were investigated.As supported by SBA-15,the impregnation sequence had little influence on the catalyst activity,while the S source significantly affected the catalytic performance via changing the degree of sulfidation of the active metal.A series of catalysts supported by carbon nanotubes(CNT)were also prepared by the combination of hydrothermal synthesis and secondary sulfuration.The optimal amount of CNT dispersion was determined,and the dispersion and the sulfuration degree of metal species were improved by adding oxalic acid.And then a highly active supported catalyst was obtained.Finally,the hydrotreating of the coal tar was investigated using the catalysts of NiMoW-Al₂O₃ and Pd-Al₂O₃.The production process of"primary desulfurization,distillate cutting,secondary desulfurization,and hydrosaturation"was proposed,and corresponding suitable treatment conditions were determined.