Preparation Of Nickel-based Nanocatalysts And Their Performance For Selective Hydrogenation Of Quinoline

1,2,3,4-tetrahydroquinoline and its derivatives are widely used in the fields of medicine and dyes,and are important structural units.In the synthetic methods reported in the literature,the selective hydrogenation of quinoline is highly economical,but this method has the disadvantages of harsh reaction conditions and easy formation of a large number of by-products.Therefore,it is important to prepare efficient and stable catalysts for the selective hydrogenation of quinoline under mild conditions.Therefore,a series of nickel-based catalysts with different structures and properties are designed and prepared for the selective hydrogenation of quinoline,and the effects of the structure and properties of the prepared catalysts on the catalytic performance are studied.Firstly,the catalyst NiSi-PS was prepared by in-situ reduction using nickel phyllosilicate as a precursor for the selective hydrogenation of quinoline.Compared with Raney nickel and catalyst prepared by impregnation,the catalyst NiSi-PS prepared by in-situ reduction shows higher catalytic activity.By further optimizing the reaction conditions,the conversion of quinoline is 99.0%.Through TEM,H₂-TPR,XPS and other characterizations,compared with the catalyst prepared by the impregnation method,NiSi-PS catalyst prepared by in-situ reduction of nickel phyllosilicate has good dispersibility of active metals,small particle size of only 3.2 nm and strong interaction between active metal and support.The stability test of the catalyst NiSi-PS was carried out,and the reasons for catalyst deactivation were discussed.Secondly,A hollow core-shell catalyst Ni@hw-mSiO₂ was designed and prepared with carbon spheres as template and used in selective hydrogenation of quinoline.XRD,TEM and other characterizations have proved the successful synthesis of the hollow core-shell structure of the catalyst.The active center nickel in the catalyst has a small particle size and is uniformly dispersed on the inner surface of the shell.The special structure of the catalyst enhances the interaction between the metal and the support,and inhibits the agglomeration of the active metal.In addition,the catalyst Ni@hw-mSiO₂ has good activity and stability in the selective hydrogenation of quinoline,the conversion of quinoline is above 95.0%and the conversion of quinoline is still above 90%after 5 cycles.Finally,A series of nickel-based nanocatalysts Ni/mSiO₂-DMBSx were prepared by the hydrogelator[DMBS:2,4-（3,4-dimethylbenzylidene）-D-sorbitol]assisted impregnation method for quinoline selective hydrogenation.The effects of the amount of DMBS on the properties of the catalyst were systematically studied,and the role of DMBS in different catalyst preparation stages was explored.The research show that the catalyst prepared with the concentration of DMBS is 0.005 g mL^-1 has the highest activity and good stability.This is due to the interaction between the oligomer formed by the self-assembly of the low molecular weight gel and nickel nitrate,which is beneficial to improve the distribution of nickel nitrate and the decomposition behavior of nickel nitrate during calcination,thereby improving the dispersibility of active metal nickel in the catalyst and the interaction between metal and support.