Investigation On The Preparation And Hydrodesulfurization Performance Of NiMo Bulk Catalysts

With the promulgation of strict environmental regulations to solve the worldwide pollution problem,the quality of vehicle fuels will surely be further improved in the future.Now,according to China’s National VI emission standards,the sulfur content of vehicle fuel provided by refineries to customers must not exceed 10 ppm.Compared with technologies such as oxidative desulfurization or adsorption desulfurization,hydrodesulfurization technology is still the main technology for effectively removing sulfur compounds in vehicle fuels,and the design and preparation of new and efficient catalysts is one of the keys to this technology.In this paper,NiMo bulk catalysts with three-dimensional ordered macroporous structure and nano-flower-like structure were successfully prepared,and their hydrodesulfurization performance was evaluated.The specific research contents are as follows:This thesis first explored the effect of the monomer addition amount,emulsifier amount,initiator amount of methyl methacrylate（MMA）during emulsion polymerization on polymethyl methacrylate（PMMA）.The influence of particle size and distribution of microspheres.PMMA microspheres with different particle size were successfully prepared,and then PMMA colloidal crystals were prepared by centrifugal self-assembly,which were used as templates for the preparation of three-dimensional ordered macroporous nickel-molybdenum bulk catalysts.Using PMMA colloidal crystals with a particle size of approximately 230nm as a template,three-dimensionally ordered microporous（3DOM）bulk hydrodesulfurization catalysts with different NiMo molar ratios were successfully prepared through precursor impregnation,drying,and calcination processes.The prepared catalysts were characterized by TG/DTG、XRD、SEM、Low temperature nitrogen adsorption and desorption、TEM、HRTEM和H₂-TPR etc.Moreover,the hydrodesulfurization（HDS）activity evaluation over the prepared catalysts was carried out through a continuous high-pressure fixed-bed microreactor.The results show that the NiMo bulk catalysts with a three-dimensionally ordered macroporous structure have the relatively high surface area,and the unique interconnected three-dimensional pore structure is beneficial to reduce the diffusion resistance of reactants/products in the catalyst pores.Among the prepared 3DOM NiMo bulk catalysts,the conversion rate of thiophene over the catalyst with the NiMo molar ratio of 1 is up to 99.4%under the reaction conditions of the pressure of 1MPa,reaction temperature of 360℃,and space velocity of 6.3h^-1.In addition,using ammonium molybdate as the source of molybdenum,nickel nitrate as the source of nickel,and thiourea as the source of sulfur,the simple hydrothermal synthesis method was used to successfully synthesize the presulfurized NiMo catalysts with the unique nano-flower-like structure.The characterization results show that all the catalysts exhibit a nanoflower-like structure assembled from nanosheets.This specific structure can provide more space for the diffusion of thiophene and desulfurization products.Furthermore,the high surface area can enable the prepared catalysts to expose more active sites to facilitate the adsorption of thiophene on the catalyst surface,thereby enhancing the catalytic activity.Due to the introduction of sulfur in the preparation process,the prepared catalysts can be exempted from the presulfurization process before the HDS tests.The HDS activity evaluation results indicates that the conversion rate of thiophene over the catalyst with the NiMo molar ratio of 1.25 is up to 99.6%under the conditions of the pressure of 1MPa,reaction temperature of 360℃.