Study On The Preparation And Catalytic Performance Of Highly-Loaded Hydrotreating Catalysts

In recent years,with the increasing emphasis on environmental quality and the growing concern about environmental protection,stringent environmental legislation to limit the sulphur content in transportation fuels?especially diesel?has been introduced throughout the world,which one of the most important indicators is transportation fuels of ultra low sulfur content?less than 10?g/g sulphur?.At present,hydrodesulfurization?HDS?process is considered as the most effective way to achieve this goal,and the high-activity catalyst is the key.Traditional HDS catalysts encounter challenging tasks when enhanced activities emerged,due to the limited loadings of active components and the strong interaction between active components and support.In recent years,experimental and industrial research shows that unsupported or bulk hydrotreating catalysts,which are prepared without using a porous support and have high metal content,have higher hydrogenation activity.But,the unsupported catalyst has some problems those the preparation process is complicated,the specific surface area is small and the active site can not be fully utilized.Based on the advantages and disadvantages of the conventional supported hydrotreating catalysts and the new unsupported catalysts,a new simple method for the preparation of highly loaded NiMoW catalyst was developed,which is preparing analogously unsupported catalysts by impregnation method generally used to prepare conventional supported catalysts.In this work,by using commercial pure silica as support which has large pore volume,high specific surface area and high water absorption,the active phase loading can reach to more than 50%through the method of co-impregnation.The catalysts prepared by this method not only have high metal content,but also have good textural characteristics.A series of highly loaded catalysts was synthesized under wide varies calcination temperatures at firstly,the effects of calcination temperature on the performance of the catalysts were investigated.Results reveal that with the increasing calcination temperatures,the stacking number and the slab lengths of MoS₂ and WS₂ on the catalysts were increasing,and the agglomeration of metal active component was more and more serious.TPR showed that as the increasing calcination temperature,the trend of low temperature reduction peak to move toward high temperature is increasing and reducing capacity of active component become weaken.The catalyst of calcination temperature in 170?showed the highest hydrogenation selectivity(S_HYD/S_DDS)and HDS activity among the series of catalysts.Secondly,these catalysts with different metal loading were prepared by co-impregnation method,the effects of metal loading on the performance of the catalysts were investigated.As catalysts loading from 35%to 52%,the decline trend of specific surface area is very small,but if increase the metal load,active compounds will happen serious plugging phenomenon,meanwhile,the decline of specific surface area of catalyst is significantly,and the activity of catalyst would decrease.The results showed that with the increasing loadind on the catalysts,HDS activity of catalysts increased first and then decreased,and the NiMoW/SiO₂-52%catalyst showed the highest HDS activity.Finally,the comparison between the optimized highly loaded catalyst and the other reference catalysts showed that the catalyst is advanced.