Performance Analysis Of Hydrogenation Of Nitrobenzene To Aniline Catalyzed By Pd And Pt Supported By Nitrogen-doped Carbon Materials

In this thesis,a series of nitrogen-doped carbon-supported Pt-based and Pd-based catalysts(Pt/N-CX_?r?,Pd/N-CX_?r?)were prepared by using nitrogen-doped carbon materials as the carrier and noble metals Pt and Pd as active components.They are used to catalyze the performance of hydrogenation of nitrobenzene to aniline.The catalysts were characterized by XRD,N₂ adsorption-desorption,TEM,FT-IR,Raman and XPS.The components of the reaction system were analyzed by gas chromatography-mass spectrometry,and the relationship between the physicochemical properties of the catalyst,the preparation method and the catalytic activity was correlated.The main conclusions are as follows:?1?The effect of different nitrogen source doping on the texture properties of carbon materials.A series of nitrogen-doped carbon materials were prepared by the method with using melamine,dicyandiamide,guanidine hydrochloride,urea,thiourea as nitrogen source,glucose as carbon material precursor,ZnCl₂ as ionic liquid,using molten salt.It was found that the sample prepared with thiourea as the nitrogen source was mesoporous,while the other nitrogen source mainly maintained the microporous structure;while the sample obtained with guanidine hydrochloride as the nitrogen source had the largest specific surface area.?2?The Pt-based and Pd-based catalysts were prepared by sol-fixation method and their catalytic performance for the hydrogenation of nitrobenzene to aniline was tested.Although the catalyst prepared by using guanidine hydrochloride as a nitrogen source has the largest specific surface area,its catalytic activity is relatively poor.For Pt/N-CX?r?,the order of activity is:melamine>dicyandiamide>guanidine hydrochloride>thiourea>urea;for Pd/N-CX_?r?,the order of activity is:melamine>dicyandiamide>guanidine hydrochloride>urea>thiourea.It is indicated that the activity has no close relationship with the specific surface area,and different nitrogen sources have a great influence on the activity of the catalyst,and melamine is the best when it is a nitrogen source.?3?Comparing the performance of 1.0%Pt/N-CX_?0.5?and 1.0%Pd/N-CX_?0.5?catalyst prepared with melamine as nitrogen source in the reaction of nitrobenzene to aniline,the conversion of nitrobenzene was 70.1%,which was much higher than40.5%of the former?the selectivity of aniline was higher than 85%?,indicating that the Pd-based catalyst is more suitable for the selective hydrogenation of nitrobenzene to aniline.?4?The effect of nitrogen doping amount on the performance of Pd/N-CX_?r?catalyzed hydrogenation of nitrobenzene.Pd/N-CX_?r?catalysts with different nitrogen doping amounts?mass ratio of nitrogen/carbon precursors of 0.17,0.34,0.5,0.67,0.83?were prepared using melamine as nitrogen source.When the mass ratio of nitrogen/carbon precursor is 0.5,the prepared Pd/N-CX_?0.5?has the best catalytic performance for hydrogenation of nitrobenzene?nitrobenzene conversion rate is 70.1%,and aniline selectivity is 85.5%?,and shows a certain cycle performance.?5?Pt/N-CX_?0.5?prepared with melamine as nitrogen source was used to study the effects of Pd content,solvent,hydrogen source,pressure,reaction temperature and reaction time on the reactivity,and optimized the reaction.condition.The optimum reaction conditions are:n-heptane is a solvent,hydrogen is a hydrogen source,the reaction pressure is 0.1 MPa,the reaction temperature is 60 ^o C,and the reaction time is 1 h.