Study On The Preparation And Catalytic Mechanism Of Catalyst Used In The Amination Reaction To Produce2,6-Dimethylaniline

2,6-dimethylaniline as an important organic intermediates, has been widely used as medicine, pesticide raw materials and dye intermediates. In this thesis, Pd/Al2O3and Pd/C were prepared and used in the amiantion reaction to produce2,6-dimethylaniline. By means of XRD, TEM, H2-TPR, TPD and XPS characterizations, the influence factors of catalyst performance were investigated. Also the mechanism of the amination reaction, the formation mechanism of active species PdHx, the the influence factors on the content of it, and even the mechanism of deactivation and the reactivation method were studied. Experimental results show that:under H2free condition of amination reaction, the active species of Pd/C catalyst is PdHx, and the higher the content is the better the catalytic performance is; Using hydrazine as reductant PdHx can generate only from PdO, and the pretreatment and reducing conditions are closely related to its content.During the preparing of Pd/Al2O3catalyst, the A12O3was impregnated with an appropriate amount of Mg(NO3)2and Al(NO3)3. And after calcination at high temperature, We got a spinel carrier supported on Al2O3. The surface acid nature of the support can be adjustd by changing ratio of the Mg(NO3)2and Al(NO3)3. By supporting1%Pd on the the best carrier with the mass ratio of γ-Al2O3:MgO:Al2O3=50:4:4, we got the catalyst H-10with the best catalytic performance.It is noticed that amination reaction itself does not consume H2, but requires a large amount of H2in order to generate the desired product. We tried to use cyclohexanone as inducing agent, to induce the amiantion reaction under H2free conditions. In this paper the cyclohexanone inducing mechanism in the amination reaction of2,6-dimethylphenol under H2free condition was deduced according to the literature and experiments. Firstly, addition reaction happens between NH3and cyclohexanone which generate cyclohexanimine; then the cyclohexanimine transfers H to2,6-dimethylphenol and generates2,6-dimethylcyclohexanone, with itself becoming aniline; Then NH3reacts with2,6-dimethylcyclohexanone to produce2,6-dimethylcyclohexanimine. Lastly,2,6-dimethylcyclohexanimine changes into2,6-dimethylaniline in three different ways. The PdHx is the active phase of this amination reaction.In addition, during the preparation and application of the Pd/C catalyst, it was too found that the the PdHx particles are the active phase of the amination reaction. Pretreated with2.5%nitric acid, the activated carbon gets a most suitable value of DTA(density of total acidity) which is favourable for the generating of PdHx particles. Catalyst with more PdHx particles is much more active. The reason of deactivation is the decomposition of PdHx caused by the high reaction temperature. Oxidation treatment of the deactivated catalyst and then reducing with hydrazine hydrate at a suitable temperature may enable PdHx particles to regenerate, and so the catalytic activity recover.In this thesis, through researching catalyst of2,6-dimethylphenol amination reaction under H2free condition, we provided some theoretical guidance on the amination of different phenols to synthesize the corresponding aniline; Also we found the the optimum conditions to prepare Pd/C catalyst containing PdHx phase and proposed the formation mechanism of PdHx in the reducing process of PdO by hydrazine. This is very useful for the practical application and the theoretical research on this kind of catalyst.