Synthesis Of Boron Nitride Supported Catalyst And Its Catalytic Hydrogenation Of Aromatic Amines To Adiocyclic Amines

The hydrogenation process for synthesizing alicyclic amines from aromatic amines often suffers from low selectivity of alicyclic amines,and requires the addition of liquid alkali to inhibit unwanted side reactions resulting in significant waste and environmental risk.To address this issue,it is important to develop a green synthesis method for alicyclic amines under mild conditions.In this study,we synthesized bimetallic Ru-Rh/h-BN,Ru/h-BN,and modified Ru/d-BN catalysts.These catalysts were utilized to hydrogenate aromatic amines to alicyclic amines.We analyzed the structure-activity relationship of the catalysts and the underlying reaction mechanisms,which could lay the foundation for efficient and environmentally friendly synthesis of alicyclic amines from aromatic amines under mild conditions.The main findings and conclusions of this research are as follows:(1)The preparation of the bimetallic Ru-Rh/h-BN catalyst was carried out for the synthesis of PACM via the saturated hydrogenation of MDA.Additionally,the structure-activity relationship of the catalyst was investigated in detail.The Ru-Rh/h-BN catalyst was prepared using the ultrasonic-assisted impregnation method with hexagonal boron nitride as the carrier.Under the interaction between the metal carriers,the ruthenium-rhodium components were highly dispersed on the catalyst surface,forming dual active sites for ruthenium-rhodium hydrogenation.Moreover,the Rh-N_x and Ru-N_x active species were formed on the catalyst surface,regulating the electronic activity centers of ruthenium and rhodium.Furthermore,the evaluation of the Ru-Rh/h-BN catalytic system and the optimization of reaction conditions were conducted.Going through a fixed-bed continuous long-cycle operation indicates that the catalyst demonstrated high catalytic efficiency even after extensive use.Finally,the catalyst universality was examined.(2)The catalyst preparation and structure-performance relationship research of single-metal Ru/h-BN catalyzed MDA selectivity hydrogenation for the synthesis of PACM were carried out.The Ru/h-BN catalyst was prepared using the ultrasound-assisted impregnation method.Characterization results showed that the formation of coordinated Ru-N_x and Ru-B_x favors the high dispersion of Ru species.The optimization of the MDA hydrogenation process and mechanism research were conducted.The results showed that both reaction temperature and initial hydrogen pressure significantly affected the reaction performance.The fixed-bed continuous long-period operation showed MDA conversion rate>99.0%and PACM yield>98.0%.DFT results indicated that the too-strong adsorption of the intermediate by the Ru/h-BN catalyst was the dominant reason for the slow rate-determining step of the hydrogenation reaction.In addition,substrate expansion experiments showed that the catalyst has good universality for catalyzing the hydrogenation of various aromatic amine compounds.(3)The preparation and structure-effect relationship of Ru/d-BN catalyst with defects was carried out for the synthesis of PACM via MDA hydrogenation.A nitrogen-doped boron nitride material rich in defect sites and amino-functionalization was prepared by urea-assisted ball milling,and a Ru/d-BN catalyst was prepared by ultrasonic-assisted impregnation method.The d-BN carrier has a larger specific surface area,exposing more defect sites,which leads to more vital interaction between the active metal Ru and d-BN.The optimization and mechanism research of the MDA hydrogenation process was carried out.The results showed that introducing defect sites enhanced the alkalinity and hydrogen dissociation activation ability of the Ru/d-BN catalyst,effectively reducing the metal loading(5.0 wt.%to 3.0 wt.%)and reaction pressure(5 MPa to 3 MPa).By comparing the experimental results of different preparation methods of catalyst and DPPH quenching activity site,introducing defect sites effectively improved the reaction rate of benzene saturation hydrogenation.DFT analysis demonstrated that modified Ru/d-BN could effectively regulate the adsorption and desorption behavior of the catalyst on the substrate,achieving a mild hydrogenation of the benzene ring with defect-regulated Ru-based catalysts.