Study Of The Direct Catalytic Amination And Hydroxylation Of Benzene

The direct functionalization of benzene either animation or hydroxylation, which involves the activation of C-H bond, preserves a challenging topic in chemistry and attracts much attention recently. Both aniline and phenol are important chemicals in industry, and are commonly produced by multi-step processes. In present work, a series of Ni-based catalysts is designed, prepared and used for the direct amination and/or hydroxylation of benzene with molecular oxygen or hydrogen peroxide and ammonia. It is found that both aniline and phenol could be obtained over the catalysts designed and prepared in present work. By adjusting the composition and/or preparation methods of the catalysts, enhanced selectivity to aniline (or phenol) could be obtained.The fundamentals of the preparation of the catalysts are studied by means of thermal analysis and ICP. It is found that supported species interact with the support even before the thermal decomposition of the catalyst's precursor.When one component is supported, these interactions affect the thermal decomposition, that is, these interactions reduce the interaction between metal ions and the coordinated water, and enhance the interaction between metal ion and nitrate group, thus the sample could release water at lower temperature and the final decomposition temperature shifts to higher values comparing to the corresponding un-supported metal nitrate, the decomposition mechanism varies also.When two or more components are supported, different supported species andcomposition and the preparation procedures of the sample. Generally, the final decomposition of the samples is facilitated by the co-existence of multi-supported species, and the decomposition mechanism changes. The final contents of supported species vary with preparation procedures by using the same controlling contents. The interaction of zirconium species with the support is greater than those between nickel or cerium and the support, resulting in a prior connection of zirconium species with the support when cerium and zirconium are co-impregnated.The catalysts used are characterized by XRD, XPS, temperature-programmed reduction, hydrogen adsorption and oxygen adsorption. It is revealed that the fine chemical states of the supported species and their distribution change with the composition and the preparation procedure of the catalysts. Zirconium species is highly dispersed. The differences in fine chemical states and their distribution give reason to the differences in the formation of nickel oxides crystallites, the formation of cerium-zirconium solid solution, the reduction behavior (especially the reduction at low temperature) and the adsorption performance of oxygen and hydrogen. Cerium or zirconium species could promote the dispersion of the co-supported nickel species, enhance the formation of low-temperature-reducible species, and thus increase the adsorption of oxygen and hydrogen, while the co-existence of nickel with cerium and zirconium enhances the formation of cerium-zirconium solid solution.The catalytic performance, the adsorption behavior of hydrogen and oxygen of the catalysts depend mainly on the dispersion and fine chemical states of surface species. Cerium and zirconium species in the catalysts are beneficial to the selectivity and yield of aniline. The catalyst number 4 is prepared by the following procedure: cerium and zirconium are co-impregnated prior to nickel, after dried (without calcination), nickel is introduced and then dried and calcined. Each component on this sample is well dispersed, few amount of cerium-zirconium solid solution and quite a few amount of low-temperature-reducible species formed on this sample. It exhibits high hydrogen adsorption capacity, moderate oxygen adsorption capacity and then high aniline formation activity and selectivity. Cerium species ispredicted to participate in the catalytic event. This particular catalyst has a rather stable composition and structure.The hydroxylation of benzene is also investigated over the same catal...