Construction Of Metal Organic Framework Assisted CoMoS Active Phase And Mechanism Of Selective Hydrodesulfurization

Transition metal sulfide is a widely used hydrodesulfurization catalyst,which is mainly used in the production of clean oil.To prepare catalysts with higher activity and selectivity,it is necessary to understand the structure-activity relationship between the microstructure of active phase of transition metal sulfides and the performance of catalysts.In this paper,Co Mo-n@ZIF-8 composite was used as the catalyst precursor.The C-N framework-limited catalyst active phase was prepared by adjusting the ratio of cobalt to molybdenum and curing conditions.The structure-activity relationship between the microstructure of the active phase and the activity and selectivity of the catalyst was studied in depth,which provided theoretical guidance for the design and development of high-efficiency hydrodesulfurization catalysts.Co Mo-n@ZIF-8 precursor was prepared by room temperature method,and Co Mo S_x-n@Zn S catalyst was obtained by vulcanization.The effects of different Co/Mo ratios on the structure of active phase and the hydrodesulfurization performance of catalysts were investigated.The results showed that the incorporation of Co Mo did not destroy the original crystal structure of ZIF.The incorporation of Co makes the Mo atom at the edge of Mo S₂ modified,hindering the growth of Mo S₂ nanocrystals along the cross section,exposing more active centers and improving the catalytic activity.When Co/Mo=0.5,the DBT conversion rate and the reaction desulfurization rate reached the highest,and the hydrogenolysis activity center was the strongest at this time.With the increase of Co/Mo,the catalytic and then increased,and the selectivity of HYD/DDS increased continuously.Since the DBT conversion of the catalyst with Co/Mo ratio of 0.5 was the highest,the Co Mo-0.5@ZIF-8 composite was used as the precursor to investigate the effect of curing temperature on the construction of the active phase of the catalyst.The results show that with the increase of curing temperature,Mo S₂ nanolayers gradually wrapped on the surface of Zn S nanospheres.It is also found that the bending degree of Mo S₂nanosheets increases and the average curvature decreases.When the vulcanization temperature is 400°C,the catalyst has the highest activity and tends to hydrogenolysis path.With the increase of curing temperature,the average curvature of Mo S₂decreases,the relative ratio of’Rim/Edge’increases,and the selectivity of HYD/DDS increases.Co Mo C_xS_y-n@CN with carbon-nitrogen framework confinement was prepared by high-temperature calcination and vulcanization using Co Mo-n@ZIF-8 as precursor.At the same time,a simple supported Co Mo C_xS_y-6/CN catalyst was prepared.The effect of Co/Mo ratio on the microstructure and properties of the active phase was investigated.Studies have shown that the composites can be carbonized and vulcanized to form Mo C_xS_y,and Co S_x can interact with Mo C_xS_y nanoclusters.When Co/Mo=0.5,the conversion rate of DBT reached the highest（56.11%）,and the selectivity of DDS was the highest.This was because the average particle size of Co-based nanoparticles was the smallest（1.62 nm）,and it could cooperate with more Mo C_xS_y nanoclusters to generate more CUS sites.Enhanced hydrogenolysis activity.With the increase of Co/Mo,DBT conversion decreases first and then increases,HYD/DDS selectivity increases.The evaluation results showed that the activity of Co Mo C_xS_y-n@CN was significantly higher than that of Co Mo C_xS_y-n/CN.