Abstract
The oxidation of benzene to phenol (BTOP) with N2O as the oxidant has been studied with a variety of Fe/ZSM-5 catalysts. The literature has conclusively proven that Fe2+ sites are the active sites. However, some studies have suggested that the Lewis acidic sites (LAS) are responsible for the generation of the active chemisorbed oxygen. Nevertheless, there is no clear relationship between the LAS and the N2O selectivity to phenol. In an effort to elucidate the effects of LAS on BTOP with various ZSM-5 catalysts, we investigated the initial N2O selectivity to phenol. Here we show that the initial N2O selectivity to phenol is negative with the amount of LAS over a certain range. The catalyst H-ZSM-5-ST (H-ZSM-5 treated with water vapor) showed a remarkable initial N2O selectivity to phenol as high as 95.9% with a 0.021 mmol g−1 LAS concentration on the surface of the catalyst, while the Fe/ZSM-5 catalyst demonstrated the lowest initial N2O selectivity to phenol (11.7%) with the highest LAS concentration (0.137 mmol g−1). Another remarkable feature is that steaming was more effective than Fe ion exchange and high temperature calcining. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2-adsorption-desorption, UV-vis, NH3-TPD and pyridine Fourier transform infrared (FT-IR) techniques. Our results demonstrate how the concentration of LAS is likely to affect the initial N2O selectivity to phenol within a certain range (0.021–0.137 mmol g−1). This research has demonstrated the synergy between the active Fe2+ sites and LAS.
Highlights
Phenol, which is an important organic chemical intermediate and raw material, is mainly used in the manufacture of phenolic resin, bisphenol A, and caprolactam
The wide-angle X-ray diffraction (XRD) patterns (Figure 1 and Figure S1) show that the intrinsic lattice structure of the MFI topology is observed in all the samples, and there is no α-Fe2 O3 diffraction peak
Through a systematic comparison of water steam treatment of H-ZSM-5 and Fe/ZSM-5 powder, we have illustrated that acidic and mesoporous properties show a significant effect on benzene hydroxylation to phenol
Summary
Phenol, which is an important organic chemical intermediate and raw material, is mainly used in the manufacture of phenolic resin, bisphenol A, and caprolactam. A commonly used industry process for developing phenol and acetone from benzene and propylene is the cumene process [1]. This process has the obvious disadvantage that phenol and acetone are used in a. A commonly used catalyst for the reaction is the H-ZSM-5 zeolites [3,4,5]. In order to improve on the activity of the H-ZSM-5 zeolites, Fe-ZSM-5 has been introduced. Iron for this catalyst can be supplied in various ways. Igor et al [7] studied Fe/ZSM-5 with a wide range of Fe content (0.015–2.1 wt.%) in the hydroxylation of benzene to phenol with nitrous oxide at low temperatures, and they found that both mono- and oligo-nuclear Fe(II) sites seem to be Catalysts 2019, 9, 44; doi:10.3390/catal9010044 www.mdpi.com/journal/catalysts
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