Preparation Of Novel Immobilized Rh Metal Catalysts And Their Application In Hydrogenation Of 4-Aminobenzoic Acid

Impregnation and microemulsion methods were employed to prepare immobilized Rh metal catalysts, respectively, which were used in the hydrogenation of 4-aminobenzoic acid to prepare 4-aminocyclohexanecarboxylic acid (4-ACCA).The hydrogenation products were analyzed qualitatively and quantitatively. According to the analytical results from melting point measurement, IR and MS analysis, the synthetic product can be identified as 4-ACCA. Quantitative analysis indicates that the purity of hydrogenation product, 4-ACCA, is 96.8% and 4-ACCA exists mainly in the form of cis structure.Impregnation method was employed to prepare a series of supported 5% rhodium catalysts, which were characterized by XRD, XPS, TEM and specific surface area analysis, and their catalytic behavior was investigated in the hydrogenation of 4-aminobenzoic acid. As a result of selection of supports, Rh/-A12O3 catalyst was found to exhibit a higher activity. And then the effects of reaction conditions on the hydrogenation performance of Rh/-A12O3 catalyst were studied. Under the reaction conditions described as follows: reaction temperature of 80 C, catalyst amount of lg and reaction time of 4h, the yield of 4-ACCA reaches 84.6%. The service time of Rh/-A12O3 catalyst was further investigated. After reused, it still shows a good catalytic activity in spite of partial deactivation. According to the comparison of characterization results of fresh and deactivated Rh/-A12O3 catalysts, the reason for deactivation was determined. In addition, the supported Rh catalyst on SiO2 oxide support was also found to show a high activity.Microemulsion method was employed to prepare a series of immobilized Rh metal nanoparticle catalysts, Rh-SiO2, which were characterized by XRD, TEM and specific surface area analysis, and their catalytic behavior was investigated in the hydrogenation of 4-aminobenzoic acid. The average Rh particle size is rather small and the size distribution is considerably narrow. And the Rh particles exist nearly in spherical shape and have a uniform distribution in the matrix of SiO2. The effect of different surfactants on structure and catalytic performance of the catalysts was studied and then Tween80/l-hexanol/RhCl3 aqueous solutionwas found to be a suitable preparation system. Then the effects of some preparation conditions such as amount of NH4OH aqueous solution, preparation temperature, Rh content and water/surfactant molar ratio were also investigated. And the effect of internal diffusion on hydrogenation process was further discussed. Over the Rh-SiO2 catalyst with the Rh content of 5% prepared by microemulsion method after milled into powder, the yield of 4-ACCA is 92.3%, which is higher than that over the catalyst prepared by impregnation method.