Hierarchically Structured FE-ZSM-5 As Catalysts For The Oxidation Of Benzene To Phenol By N2_O

Phenol is an important industrial intermediate in the production of various chemicals. At present, the main process for the production of phenol is the cumene process, which produce acetone as the co-product, resulting in that the process is limited by the demand of acetone. In recent years, much attention has been attracted by researchers on the direct oxidation of benzene to phenol (BTOP), which exhibits many advantages such as low production cost, simple and environmentally friendly process. Among the direct oxidation processes, the most promissing one is the BTOP method using N2O as the oxidizing agent and Fe-ZSM-5 as the catalyst, in which the selectivity for phenol is as high as 100%.In the BTOP process, the diffusion of benzene and the product of phenol in the micropores of ZSM-5 is highly restricted, resulting in the formation of coke, micropore blockage in the zeolite and followed by the catalyst deactivation. In this thesis, hierarchically structured Fe-ZSM-5 zeolites have been synthesized by the addition of silane coupling agent to the conventional ZSM-5 synthesis system. Because the internal mass-transfer limitations of the hierarchical Fe-ZSM-5 zeolites are significantly improved, and the impact of coke on the zeolite activity are alleviated, so the more the better catalytic activity and stability in the BTOP reaction. After alkaline steaming treatment, the hierarchical Fe-ZSM-5 show an improved catalytic activity. The main contents consist two parts as follows:1) On the basis of the previous work in our research group, hierarchical Fe-ZSM-5 zeolites have been synthesized with nine of hydrated ferric nitrate as the iron source by the hydrothermally synthetic method. The catalytic oxidatation of benzen to phenol has been performed on the steaming activated Fe-ZSM-5 samples. Various techniques such as XRD, SEM, TEM, N2 adsorption-desorption, UV-vis and NH3-TPD etc have been used to characterize the synthesized hierarchical Fe-ZSM-5. The results show that the hierarchical Fe-ZSM-5 zeolites have been synthesized by introducing the mesopores with the aid of the silane coupling agent GPTMS and thus the mass transfer properties are improved. In the N2O oxidation of benzene to phenol (BTOP) reaction, the synthesized hierarchical Fe-ZSM-5 zeolties exhibit a higher activity and stability compared to the commercial Fe-ZSM-5.In addition, we examine the effect of the ratio of Si/Al and iron content of Fe-ZSM-5 on the catalytic perfromace in benzene to phenol reaction, indicating that the lower of the ratio of Si/Al as well as the higher of the Fe content within a certain range, the higher of the catalytic activity.2) The synthesized hierarchical Fe-ZSM-5 has been posttreated by the ammonia steaming at various ammonia concentrations. The characterizations of XRD, SEM, and N2 adsorption indicate that the ammonia steaming treatment exerts less impact on the framework and pore strucutre of zeoltes, compared with the neutral steaming treatment. The ammonia steaming treated Fe-ZSM-5 exhibits excellent cataytic performance in the BTOP with N2O as oxidant, benifiting from more mid-strong acidic sites and acitive non-framwork irons in amount, confirmed by NH3-TPD and UV-vis, respectively.