Effect Of Carbon Doping On The NiMo-based Hydrodesulfrization Catalysts

With the increasing of global oil consumption,the high-quality crude oil gets less and less,and the sulfur content in crude oil has increased.Thus,the environmental pollution caused by sulfur combustion has become serious.A series of environmental regulations around the word have been imposed to further reduce sulfur content in fuel.Therefore,it is particularly important to develop the efficient hydrodesulfrization(HDS)catalysts for oil products.In this work,the effect of carbon doping on the structure and the HDS performance of the NiMo/Al2O3 catalyst has been studied in view of the strong interaction of the alumina and metal components.Firstly,Al2O3 was modified by polydopamine(PDA)pre-coating,and the effect of preparation method,calcination atmosphere and calcination temperature on the HDS activity of NiMo/Al2O3 catalyst was investigated.The experimental results show that the catalyst(NiMoAl@PDA-500Air)used Al2O3@PDA as support,coimpregnated active metal components and calcined at 500 ℃ in air exhibits the highest HDS activity.Secondly,the effect of PDA pre-coating on the phase structure,physicochemical properties and HDS performance of the catalyst was discussed via XRD,BET,TEM,XPS,TPO,H2-TPR analysis.It was found that the improvement of HDS performance mainly caused by the decreasing interaction between the PDA pre-coating and the active phase precursor,promoting the dispersion of the active phase and thus easier to reduction-sulfidation.Moreover,residual carbon resulted from the calcination of PDA pre-coating may form a more active NiMoC phase during the sulfiding process.With the increase of dopamine content in the tris buffer,the HDS activity of the catalysts shows a volcano-type change.When the dopamine content in the tris buffer is 1 mg/ml,the prepared catalyst NiMoAl-1 posses the best HDS performance owing to the shortest MoS2 slab length,the largest stacking layer number and the best dispersity of active phase on the nanoscale structure.Finally,various NiMoS-C composites were prepared with glucose and graphene oxide as carbon sources.The introduction of carbon can improve the HDS performance of nanoflower-like C@NiMoS catalysts.However,the high calcination temperature leads to long MoS2 slabs on the catalyst,and the carbon formed by glucose carbonization may cover some active sites,which is unfavorable to HDS reaction.The NiMoS-GO catalyst prepared with graphene oxide as carbon source and hydrothermal at 140 ℃ for 3 days shows the best HDS activity,while the formation of NiSO4·6H2O may inhibit the development of NiMoS active phase,resulting in unsatisfactory HDS activity.Those NiMoS-C catalysts still need to be studied,changing the synthesis strategy to optimize the morphology and structure of the catalyst for the improvment of HDS performance.