Preparation Of Highly Efficient Catalysts For Selective Hydrogenation Of Quinoline Compounds

High value functionalized 1,2,3,4-tetrahydroquinoline,as a key intermediate,has an important application in the fields of fine chemicals,such as medicine,alkaloids,pesticides,etc.The primary synthesized method of which is the selective hydrogenation route with high atomic economy,but still suffer from the problems of harsh reaction conditions,poor selectivity and stability.Therefore,it is urgent to develop an efficient catalyst for selective hydrogenation of quinoline under mild conditions.Herein,a highly active Rh-based catalyst was designed and its catalytic performance for quinoline hydrogenation under mild conditions was investigated.The details are as follows:（1）The Rh₂O₃/SiO₂ catalyst was prepared by impregnation method using inert SiO₂as the carrier.It was found that the catalyst exhibited excellent performance in the hydrogenation of quinoline under mild conditions（50 ^oC,5 bar H₂）,yielding>99%conversion and selectivity for 1,2,3,4-tetrahydroquinoline,as well as a high TOF value of520 h^-1.Moreover,the catalyst exhibits good cyclic stability and substrate universality.XPS,FT-IR,HRTEM and other characterization showed that the hydroxyl groups on the surface of the catalyst and more metallic state Rh species constructed an appropriate sites to activate quinoline molecular,endowing the catalyst with excellent catalytic performance under mild conditions.（2）Single-atom,subnano cluster and nanoparticle Rh-based catalysts were prepared by adjusting the loading of metal Rh on acidic FePO₄ support,and the corresponding hydrogenation performance was investigated in the selective hydrogenation of quinoline.The results showed that the Rh sub-nanocluster catalyst had the best catalytic performance with a TOF of 353 h^-1 in comparison with the single-atom and nanoparticle catalysts under mild conditions of 50 ^oC and 5 bar H₂.Meanwhile,the catalyst exhibit good stability and substrate universality.HAADF-STEM,XPS and CO-DRIFT characterizations indicated that acidic FePO₄ support promoted the adsorption of quinoline molecule,and Rh subnano cluster was more conducive to the dissociation of H₂ molecule,both of them promoted the improvement of catalytic performance.（3）The effect of different reduction temperature over subnano clusters Rh/FePO₄catalyst was studied on the selective hydrogenation of quinoline compound.The results showed that the catalyst activity decreased instead with the increase of reduction temperature,in which the catalyst reduced at 75 ^oC showed the best catalytic performance.H₂-TPR,TEM and XPS characterizations demonstrated that with the increase of reduction temperature,the metal Rh species exhibited more metallic state,which resulted in that the interaction between the catalyst and quinoline substrate was too strong,leading to the inferior catalytic performance.