The Study Of NiMo Hydrodesulfurization Catalyst Supported On FDU-12-based Molecular Sieve

Nowadays,hydrodesulfurization?HDS?is one of the most important processes for clean fuel production,in which HDS catalysts with high activity play a critical role in achieving deep desulfurization.In this thesis,a series of mesoporous materials with different pore diameters and structures and aluminum loadings were synthesized as supports.The corresponding catalysts were prepared by the incipient-wetness impregnation method and evaluated using the model compound dibenzothiophene?DBT?.The objective of this work is to explore the influence of the support pore diameter and structure on the active phase morphology and HDS performance,moreover,to research the effect of the support modification with aluminum on the dispersion of active components,the HDS activity and selectivity.Firstly,a sequence of mesoporous materials FDU-12 with different pore diameters and structures were controllably synthesized by changing the hydrothermal temperature.The corresponding catalysts were prepared by loading NiMo active components over the abtained FDU-12 supports and then tested in the HDS reaction of DBT.The results showed that when the supports prepared at low hydrothermal temperatures?T<150 ^oC?,the obtained catalysts showed straight MoS₂ nanoparticles but the corresponding HDS ratios were low because the small window sizes of the supports seriously hindered the contact between the reactants and the active sites.Increasing the hydrothermal treatment temperature to 150 ^oC,the corresponding catalyst displayed curved MoS₂nanocrystallines due to the confinement effect of the spherical pores of FDU-12 and this catalyst exhibited the highest HDS ratio?94.5%?because of its large pore diameter and three-dimensional open pore structure favorable for the molecular diffusion.Further increasing the hydrothermal treatment temperature,a closed MoS₂ structure was formed on the support with a poor dispersion and thus the corresponding catalyst showed a bad HDS performance.When the hydrothermal temperature was raised to 210 ^oC,the window size was enlarged to be almost close to the cage size and the pore structure was proposed to be turned into straight-like channels.The correspongding catalyst showed highly straight and poorly-dispersed MoS₂ particles with the lowest HDS activity.Based on the above research work,we obtained the most favorable mesoporous structure of FDU-12 used as the hydrodesulfurization catalyst support.Then,a series of Al-FDU-12 with different Si/Al molar ratios were synthesized and the corresponding NiMo catalysts were prepared.It was found that as increasing the Al content,the metal-support interaction was enhanced resulting in the improved dispersion of active components.The HDS activities of the catalysts increased first and then decreased with the best performance at Si/Al molar ratio of 30.Finally,we chose NiMo/AF-150-30 as catalyst to investigate the HDS reaction pathways of 4,6-DMDBT and the result showed that the isomerization pathway?ISO?was improved significantly,which is expected to be applied to the removal of the macromolecular sulfur compounds.To illustrate the effect of the support structure of HDS catalyst on the active phase morphology and desulfurization performance,SBA-15 and FDU-12 mesoporous materials were chosen as supports for comparison.SBA-15 and FDU-12 were also modified with Al to obtain Al-SBA-15 and Al-FDU-12.The four kinds of material were loaded with different mass fraction of MoO₃?6 and 13 wt.%?and Ni additives,respectively.It was found that when the metal loading was low,the HDS activities of NiMo supported on FDU-12 and Al-FDU-12 were both higher than that on SBA-15 and Al-SBA-15,because the large pore size and three-dimensional open pore structure of FDU-12 are more favorable for the reactants diffusion.While at the high metal loading,the catalytic activity of NiMo/FDU-12 was lower than NiMo/SBA-15 due to the poor MoS₂ dispersion.However,the HDS ratio of the NiMo/Al-FDU-12 was 4.1%higher than NiMo/Al-SBA-15 because the improved dispersion of active phases after modification with aluminum and the formation of curved MoS₂ with a higher activity.Meanwhile,the superior structural properties of FDU-12 also played an important role.