Preparation And Aromatic Ring Opening Performance Of Bifunctional Unsupported Ni-Mo Catalysts

With the increasingly requirements of environmental regulations and the quality requirements of diesel,the content of sulfur,nitrogen,cetane number and density of diesel fuel are controlled.Unsupported catalysts have high hydrogenation activity and can achieve deep saturation of polycyclic aromatic hydrocarbons.However,due to the lack of acidic components,the selective opening of naphthenes cannot be carried out and the cetane number of diesel cannot be increased.Therefore,it is very promising to study unsupported bifunctional catalysts with hydrogenation and ring opering.The ZSM-5 zeolite precursor was prepared in an alkali-free system.The results showed the excessive of crystallization temperature,crystallization time and the ratio of Si/Al promoted the zeolite nanoclusters to generate microcrystalline structures.The ZSM-5 zeolite precursor with a crystallization temperature of 120 ^oC,the crystallization time of 3 h and the Si/Al ratio of 45 was used to modify the Ni-Mo composite oxides.It was found that with the increase of the amount of zeolite precursor,the acidity and specific surface area of the catalyst increased,but the pore diameter decreased slightly.The naphthalene hydrocracking activity results showed the cracking activity increases with the increase of temperature,but the conversion of naphthalene decreases,and the selectivity increased with the increase of zeolite precursor addition.When the amount of zeolite precursor is 0.50 mL·g^-1 of Ni-Mo composite oxide and the reaction temperature is 380 ^oC,the selectivity of ring opening was 10.8%.Bifunctional catalysts were prepared by different synthesis methods,and the catalyst prepared by high-temperature crystallization method had better specific surface area and pore structure with the appearance of B acid sites.The effects of content of zeolite precursor,preparation conditions?crystallization time,crystallization temperature,Si/Al ratio,calcination temperature?on the structure and properties of the catalyst were investigated.It was found that when the amount of zeolite precursor solution was 0.5 mL·mL^-1 of the Ni-Mo precursor slurry,the crystallization temperature was 120°C,the crystallization time was 5 h,and the Si/Al ratio was 45,the catalyst had better specific surface area,pore structure and acidity.The calcination temperature also affected the phase properties of the catalyst.As the calcination temperature increases,the pore structure of the catalyst deteriorates and the acidity also decreased,the optimum calcination temperature was 300 ^oC.The naphthalene was selected as the model compound to evaluate the performance of the catalyst hydrogenation and ring opening reaction.The results showed that with the increase of reaction temperature,the conversion of naphthalene decreased,and the ring opening selectivity increased first and then decreased.At the same temperature,the conversion rate of naphthalene increased first and then decreased with the increase of crystallization temperature,crystallization time and the Si/Al ratio.The selectivity of ring opening increased with the increase of crystallization temperature and crystallization time,and decreased with the increase of Si/Al ratio.When the reaction temperature was 360 ^oC,the crystallization temperature was120 ^oC,the crystallization time was 7 h,and the Si/Al ratio 45,the hydrogenation active site and acid site of the catalyst was well matched,the naphthalene conversion rate was 96.7%,and the selectivity of the ring opening was up to 31.7%.