Synthesis And Catalytic Performance Of Metal-modified Over-sized SiO₂ Foam Materials In The Hydrodesulfurization Of FCC Diesel

In recent years,the fog and haze weather shrouded the major cities in China.It brings great harm on people's health and normal life.It was found that the emission of vehicle exhaust is one of the main sources of fog and haze weather.And the sulfide is believed to be one of the key pollutants.In order to solve the sulfide emission problem,the stringent specifications of high quality transportation fuels were established in many contries of the world,in which the sulfur in fuels must be reduced to ultra low level.And the development of novel hydrotreating catalysts with high activity and good performance is one of the most effective approaches to produce the clean diesel.As we all know,there are many sulfur-containing compounds with different molecule sizes in diesel,which can be divided into two types: non-heterocyclic sulfur compounds?easy to be removed?and heterocyclic sulfur compounds?hard to be removed?.The latter types contain dibenzothiophene?DBT?and its derivatives which have large steric hindrance of alkyl substitutes.Thus the removel of sulfur is the key point to produce ultra-clean diesel.Not only large pore size and open porous structure,but also sutiable acidity and good active metal dispersion are needed.Since the large pore size can eliminate the diffusion resistance and enhance the accessibility of active sites to the reactant molecules.Therefore,the development of novel support with large pore size and suitable acidity is the key in the preparation of highly active HDS catalysts.In this thesis,a series of mesoporous materials using micromulsion templating method were prepared.The ultra-large mesoporous silica foams materials were synthesized by changing the micelle expanders?mesitylene,1,3,5-triisopropylbenzene,cyclohexane and hexane?in a three-component microemulsion system?tri-block polymer?P123?+ oil phase?micelle expander?+ H₂O?.And the synthesized mesoporous materials were modified by different metals?Al and Zr?and were prepared to the corresponding catalysts,then characterized by using SAXS,SEM,BET and UV-Vis methods.Finally,they were used in FCC diesel and macromolecular sulfur-containing model compounds such as DBT to evaluate their hydrodesulfurization performance.The main contents of this thesis include:First,ultra-large mesoporous silica materials using different micelle expanders including hexane,cyclohexane,TIPB and TMB,were successfully synthesized by the template of polymer surfactant of P123.The as-synthesized SBA-16@hexane was modified by alumina to increase its acidity.The corresponding HDS performances were evaluated using DBT as the probe molecules.The analysis results demonstrated that NiMo/Al-SBA-16@hexane catalyst had an Im3 m structure with the large pore size?9.6 nm?.Compared with the converntional NiMo/Al-SBA-16 and NiMo/Al₂O₃ catalysts,NiMo/SBA-16@hexane showed the highest DBT HDS efficiency,which could be ascribed to its large and ordered pore channels.Moreover,it did not deactivate after 100 hours.Secondly,a series of Al-containing mesostructured cellular silica foams with different Si/Al molar ratios?10,20,30,40 and 50?were prepared by post-synthetic method using aluminum isopropoxide as alumina source.All the synthesized samples were characterized by SAXS,SEM,BET and ²⁷ Al MAS NMR methods.It was found that aluminum isopropoxide introduced into MCFs by the post-synthetic method had a little influence on the mesostructure of the parent MCFs and the intensity of the acidity increased significantly with increasing Al loading and reached the strongest when the molar ratio of Si/Al ratio was 20.Besides,the sulfidation level of NiMo/Al-MCFs?20?was the highest and the stacking layers were relatively low.All the prepared catalysts were evaluated by adopting dibenzothiophene?DBT?as the probe reactant.And the NiMo/Al-MCFs?20?displayed the outstanding catalytic performance.When WHSV is 20^-1,the DBT HDS efficiency was up to 96%.Finally,a series of Zr-containing mesostructured cellular silica foams with different Si/Zr molar ratios?10,20,30,40 and 50?were prepared by post-synthetic method using zirconium oxychloride as Zr source.All the synthesized samples were characterized by SAXS,SEM and BET methods.It was found that zirconium oxychloride had a little influence on the mesostructure of the original MCFs and the intensity of the acidity increased significantly with increasing Zr loading and reached the strongest when the molar ratio of Si/Zr ratio was 20.All the prepared catalysts were evaluated by adopting dibenzothiophene?DBT?as the probe reactant.And the NiMo/Zr-MCFs?20?displayed the most outstanding catalytic performance.The HDS efficiency was up to 97% and the HDN efficiency was up to 98%.